Hello , I am a bit lost about some small issues i am having and the shop manual says it could be the check valves on the arm or bucket group . has anyone ever accessed these check valves with the control valve on the machine ? it seems impossible based on what i am seeing . i am hoping that i am wrong .. What i also want to know is what is the procedure for adjusting the safety suction valves ? there seems to be some adjustment on some of them but i do not know what it does ? a longtime ago someone came and really messed up my machine and i think they interfered with that also. the shop manual has no information on adjusting this , they are the one that is labeled A
A should be your port relief. B should be the "suction" valve. A controls the maximum pressure between the valve and cylinder/motor. B keeps the cylinder/motor from cavitating under gravity or when the opposite side port relief opens
what are the symptoms that makes you think about port relief
Safety suction valves are all one piece. There can be individual safety valves and suction valves. The valves with no adjusters on them are not meant to be adjusted. Some of those are safety valves and some are suction valves. You have to have the right cartridge installed in the right port for proper operation of that function. You also have an arm regeneration valve mounted to the back of the main control valve block and an arm counterbalance valve that I never did figure out how to get to. I had plenty of trouble with those in the early years of that model machine. As I recall those port reliefs were set above the main relief on those machines. The one you had to watch out for was the arm port relief because on some ranges of excavators Komatsu set the port relief for arm out lower than the main. This I believe was in the mistaken belief that people would use that function to lift loads and set them outside of the tipping range of the machine. Some machines also came with load locks on the arm and boom cylinders. These units used pilot pressure from the joy sticks to unlock a valve that held oil in the lift side of the cylinder before it could set the load down. There were no load lock valves for the bucket circuit that I am aware of and I can't think of any check valves in either arm or bucket circuits. As Hydaumind says "what are the symptoms you are experiencing"?
well . the reason i think that is because a couple years ago we had a guy come in and mess up everything . i think he adjusted them to try to change relief pressures etc .. but he failed miserably . machine was never the same . he took out the control valve three times . rebuilding it twice because he swore that was the problem . we even bought a new control valve and he messed that up . he made us buy a new pump trying to solve this also.. all of this was done because he got a reading of 750psi from the "main pump" .. which was actually the pilot pump and he swore it was the main pump... the initial problem we had before all this was dying down and black smoke while digging ... i was much younger then and not into it that much . but now he messed us up really good . and i have spent alot of time trying to solve this i have done everything by the book and noticed that if this guy could think that the pilot pump test port / assembly was main pump pressure maybe he adjusted all those safety suction valves thinking they were all main pump reliefs ? and this is not in the book ... when i look at them they looked tampered with .. The only functions that reach relief pressures are the arm which is slowish 360-380kg/cm2 , the bucket which is kind of normal except killing machine engine alot when relieved 320kg/cm2 or around there , black smoke etc. TVC valve is not responding to adjustment and the boom which is slow on raise but does reach relief pressure and also kills the engine when relieved , i was thinking maybe it is slow due to a bad LS-EPC valve which i have a new one on the way.. swing goes to 266kg/cm2 . one track hits RH 240 and the other LH 140 . what i did notice today is that when tracking or lets say when relieving the LH track the arm does not pass that pressure when relieved (same pump) only when track lever is let go arm reaches relief pressure ... i checked main relief valves , i checked TVC solenoids . i checked pilot pressure , i checked main pump pressures directly . i checked 2 stage relief valve , i changed LS shuttle Valves for arm and bucket group , i checked pressure compensation valves but were not too sure about them . i know the right ones were in place but not sure of there operational status (what to look for etc) , i adjusted TVC valves countless times (rear pump recently started to not take adjustment and kill the engine) i have a spare .. i suspected swivel joint but i doubt it .. tracking issues show when tracking / relieving in both directions . same readings also .. machine tracks fast on level surface , responds quickly . weakness shows up when climbing . sometimes it wont even move up rough hills and just stay at there low reliefs and we have to use bucket / arm to help .. so after all this i thought about the suction valves / port relief valves ...
You need an expert to help you doing the job, this is the fastest way. A good way to start is to have a good mechanic flowmetering the pump and adjust it again as factory set if it is still in good shape in other word not leaking. Then you can continue with pilot system and of course the main control valve.
ok i understand that . only problem is i am probably the best Komatsu guy in my whole country right about now .. i could probably find a expert that works with cat or something to help me do the flow metering .. i did have the pump working good at one point . but the machine was parked for a while and i am guessing that something got stuck in the strainer / filters for the TVC valve on the rear pump so maybe that is why i am not getting adjustment ... i am sure if i get a main control valve to just swap out i will be better off ... i was wondering if the spools are mixed up for some reason .. would this cause these issues ?
Sounds to me like you have a world of issues to try to solve. I don't think there are many anywhere that could provide the kind of information you need to solve all the issues. What was changed in the pumps? Are all the valves and cartridges installed in the right places? Is there something plugging up some sensor lines? Are the electronics hooked up and set up properly. Were it my problem I would start at the pump and make sure it is working properly before anything else. You can use the speed of the tracks as a poor man's flow meter as long as the swivel and travel motors are working properly. Some kind of timer is necessary. Paint one pad on each track. Pick up that side of the machine with the implements, put the travel in high speed mode. Start the track turning to full speed and start timing the revolutions after the track has made a full revolution at speed. I used to do three turns to time. This will at least show you which pump is low and by how much. The pressures you are giving are way out of spec. Pilot pump pressure as I recall was 425 PSI. Implement pressures in normal mode were 320 KGCM2 or about 4,500 PSI and in travel or power max should be around 360 or around 5,100 PSI. The scenario you are describing tells me the pumps are not destroked at the proper pressures. The one thing that has not been addressed in your post is the compensator valves. We didn't have much trouble with those in the 200 class of machine like the 300 class but at times they were an issue. They can be resealed but most people of that era just replaced them. If one leaks through then the problem shows up on most all the functions. You might try swapping one from each side of the valve and then check something that doesn't involve two pump function. One track at a time locked up so it goes over relief might do the trick. I'll keep thinking a bit about this and let you know if anything else come to mind. Good Luck!
Thanks alot. i will start at the pump and work my way up . they bought a whole new pump assembly in error . i saw in another one of your posts that when the arm and boom are working together , arm in & boom raise , boom would come to a complete stop . i do experience this . this is why i thought about the check valves for arm and boom circuit .. sometimes it will get a little faster while pulling in the arm . but the boom is not too much faster when operated by itself anyway . i was thinking maybe something is out of place somewhere .. like a mixed up spool arrangement ? the press compensators are all in the correct places i did check this . but i think they may need re-sealing i am not sure . i did a little test with my finger covering the hole on a few of them whilst i pressed the assembly in to check for leakage . it seemed fine but that is in a low pressure situation .. so i will consider this . maybe see if i can get a seal kit for all of them . by the way i do have pilot pressure within spec now. that test they did was a longtime ago when they initially messed up the machine . i checked the safety suction valves /port reliefs today . they all seemed fine . what can cause the tvc valve for the rear pump assembly to not respond to adjustment ? this pump never crosses around 320kg/cm2 when using bucket relief so maybe the relief is set properly for this one .. but it does not de stroke i think and it kills the engine under load .i tried adjusting the valve according to the manual. but only the front pump (arm group) responded correctly to the adjustment . i adjusted the TVC valve for bucket group numerous times trying to get feel with machine on while some one was relieving the pump on and off while i did it . The funny ting is the pump for the arm develops the same pressure and more and it does not kill the machine . i guess it is because that one is working better . engine speed drops from 2150rpm to about 1850rpm while maintaining 380kg/cm2 (which i need to fix tomorrow to 320) ( also need to adjust the Tvc on this to get the engine speed to spec while on arm relief ) i do have a spare TVC valve assembly so i will consider swapping it to see if i get any change with respect to the dying down issue .. Thanks alot for all of the support . i just hope i don't end up having to pull out the control valve to get to the check valves !
ok so today i changed the TVC - LS valve . adjusted main relief for arm and bucket group to spec . machine generally feels better because he TVC valve for bucket group was faulty and causing the machine to die down unnecessarily .. what i did notice today is this . if the arm is pushed out while using boom raise the boom goes up much faster .. i am trying to figure out why this happens .. when arm in is used the boom is slowed down totally .
I'm trying to figure out what you mean by TVC valve for the bucket. As I recall the TVC stood for Torque Variable Control and that was on the pump. I'm not aware of anything like that on the an individual circuit. There was a variable control for an auxiliary function like a thumb that was an option back in those days. What is the serial number of your machine?
A80771 when i say bucket group i mean all of the associated functions on that pump . service manual refers to it as this . anything associated with rear pump is bucket group (bucket , RH track , Boom). anything associated with front pump is arm group (arm, LH track , swing) .. tvc valve for bucket group was stuck or something and not de-stroking when necessary therefore killing the engine when digging and raising boom but arm pressures were good and maintaining pressure while relieved and not killing the engine . i changed this assembly and it is fine now .
I was hoping that I was just mis-understanding the terminology. My brain cells are getting a bit worn and I thought I might have forgotten things more than I had. Sounds like you have the machine at least in a working condition now. Good Work! I'll have to study a book before I could comment on the boom and arm speed issue. Have you tried the cycle time test on your tracks yet?
Is that the one has the 22mm jam nut and an eccentric spool with a dot on the end?
haven't had time to do the cycle test yet . yes machine actually works now it is just a bit slow . i have made a major break through yesterday . The LS lines and Main pump lines where not mounted in there correct positions .. i then checked solenoids and pressure sensors associated with the Main pump and Computer to ensure they were not mounted incorrectly ... since i swapped the LS lines and main pump lines the machine has alot more power . but is still on the slow side all around . I am guessing it needs tweaking / tuning ? I still have one track that is low on power compared to the other . what i noticed with this issue is that when i relieve the side with the least power (Front pump) i get the other pump building the same amount of pressure that the front pump builds .. but when i relieve the other side which gets a decent amount of pressure (not full but closer) 260-280kg/cm2 this does not happen .. the front pump remains at unload pressure so lets say i get 150kg/cm2 on the front pump while relieving left track . the rear pump also acts like it is getting a signal to stroke up . so it builds pressure to 150kg.cm2 if i hold the lever or use other functions the front pump would momentarily gain more pressure and also attempt to track with more power.. but it seems like something is restricting it somewhere . this pump is good i think the problem switched sides when i swapped the main pump lines .. what i want to know is if incorrectly placed spools will cause some of my issues ? i think that maybe they are incorrectly placed . anyone has any information on the spool placement ? the shop manual does not go into too much detail with this .
yes that is the adjustment point for TVC
The travel circuits are separated unless another function is used. I'm thinking that something is making the merge valve open when it shouldn't.
makes sense . i was wondering if the LS portion of the merge valve is sticking ..
do you think that spools placed in wrong places can cause some of my issues ?
ok so another small update is when the track lever is moved on the problem side the pump doesn't even stroke up . it just sounds like nothing is happening . the engine tone doesn't change or nothing .. its like the system is at idle . the other side on the other hand seems normal ..
I was thinking the merge valve was controlled by the pilot circuits. I'll have to study the book a bit to make sure.
yes it is .. more updates to the problem , when you slightly pull in the stick the weak track gets all the power in the world ... and u hear the pump stroke up . with the track lever alone on the weak side the pump doesnt stoke up . any one function on that pump and it doesnt stroke up . when you merge the two pumps machine works almost normal besides the weak track . i am going to try tracing all lines to make sure all are in correct places and work my way up from there .. adjusting LS valve on pump or tvc valve on pump creates no change . i believe it is a control valve issue because when i switched the main pump lines and the LS lines that were crossed the problem switched sides ..
ok so i dont know if this is related to the problem but a hissing noise is always heard from the control valve .. no matter the position of safety lever . it is loud enough to hear with the machine revving at high idle .. i dont know what is by passing where .. it is hard to pin point but definitely coming from control valve . i thought about the swivel but it does not sound like it is coming from there .. this sound is heard while evrything is at neutral . i have not checked for the noise whilst operating functions . i will do this tomorrow . i was thinking that i can try disabling (i am not sure how) the Pilot Pressure control pump to rule out any Pilot pressure issues ..
Hissing noise is normal, it is oil flow being unload to tank. You can check other machines and hear the same
Second hydraumind work on a pc400 and has always had same hissing. Does this machine have ppc shuttle valve?
yes it does
so what can cause the track to speed up when the stick is pulled in slightly ? very noticeable speed difference in weak track (front pump) .. and very slight difference in other track (rear pump) The weak track barely builds pressure , the better track almost reaches relief pressure (260-280kg/cm2)
Pump flows are merged when you use travel and another function. Have you done the track cycle time yet?
i will do this today . but i can tell you that the weak track has a cycle time of over a minute .. but the weak track and arm are on the same circuit .. would this be a merge situation also ? and will the merge affect travel speed ? and if i pull in the lever right in it would not work no other function makes the track spin faster other than just slightly pulling in the arm lever like one inch . if i pull it more than this the track will sort of jerk fast slow fast slow .. any more than this and no change .
What mode do you have the machine in when you are running these tests? The computer has a logic to it that gives the best operating characteristics depending on the mode selected by the operator. You should be in the GO or HO modes when doing these tests. Are you aware that there is a straight travel valve that allows joined flow between the travel motors when the machine is traveling straight? If your travel is drifting to one side I would suggest checking case drain flow on the slow travel side. If that is good, I would check out out the swivel next. The other issue is whether or not the weak travel side is sending a load sense signal to the pump to stroke up. Depending on machine mode the arm is a two pump function so using it while engaging the weak travel will cause both pumps to stroke up and the merge valve to open. Is it possible to check the LS Differential pressure for the travel by itself and the arm by itself? That might tell you if enough pressure is felt on the LS line to get the pump to stroke up. I would think you could have compensator leak on the travel is that is the case. All this points to the reason I got to not like working the Dash 6 line. They are just too complicated a system just to move some dirt around. They are great when they work properly. They are time consuming and expensive to have to fix when something goes wrong and nobody at the factory level will share any information on how to find and fix the problems.
ok for starters everything associated with that pump with the pumps split is slow . not so weak . tests are always carried out in H/O mode so i am talking about arm , LH track and swing .. they are all slow . it was the other way around before i switched the LS lines and Pump lines . meaning that everything associated with the rear pump was weak before Boom , RH tack and bucket . so i am thinking that it is something associated with the LS system.. when the pumps are split and i pull in the stick just a little the track spins faster . pumps stay split based on my readings on codes 11 and 12 ... when the pumps are merged the arm is faster and stronger . and swing is faster . the track remains the same . The funny thing is both the LS lines and main pump lines were in the wrong places . when i switched them the problem went from one side to the next .. so i dont know if its a pump tvc ls valve issue or control valve issue . what i can probably do is swap the LS lines and see if i get any change ? i am confused here now .. on your last point about the track sending a ls signal . i doubt very much that any of those functions are sending a LS signal . because the pump never strokes up .. what can i do to check this ? point me in the right direction to check thoroughly the entire LS system . all places to check .. i did change the LS shuttle valves so i may rule those out ...
You need a differential pressure gauge or two accurate gauges to check the LS differential pressure. Two gauges are installed on the pump outlets and to more gauges are installed on the LS ports on the pumps. When you operate a function the LS pressures should read somewhat less than the pump pressures. That difference was somewhere around 300 PSI as I recall. I has been some years since I've had to check this so I don't recall exactly the procedure but I know it is in the service manual. You can likely just plug into the LS port to see if you get any pressure at all. I would also suggest scoping the book out close and make sure you have all the hoses hooked up in the right place. It is a pain trying to follow the hydraulic schematic and then tracing the hoses from end to end but it sounds to me like that is what you are going to have to do. Good Luck
ok i will do this . just have to make two more hoses and one more gauge
ok so i found an error that me and my service manual made .. i have two different service manuals and the two of them have the main pump lines going to control valve marked in different places . it looks like one had an error . so i need to switch my main pump lines back to normal . the LS lines were in the wrong place for sure .. the two manuals in question was one specifically for my pc220lc-6 (the correct one i think) and the other from pc200-250lc-6
if any one can shed some light on this for me because it seems like some are mounted opposite or maybe it is an error . i will try mounting the other way and see if i get any results ? Maybe this explains why the front pump was not stroking up when it was suppose to .
ok so i switched the main pump lines and the problem switched sides . so now all along i thought it was the front pump that was not stroking up when the reality is because the lines were not on correct it is the rear pump that is not stroking as it should .. tomorrow i am going to do a Differential pressure test . i should have all my fittings etc by then .. the front pump is working good now for arm etc .. the tracking issue switched sides .. so i guess this problem lies in either the TVC valve or LS system for that side ...
I think there are different books for a serial number break. My book had PC200LC-6 for serial 80001 and up. There is a serial number break starting at 88000 and up. It has PC220LC-6 for serial number 50001 and up. There is a serial number break at 52000 and up. What is the serial number of your machine? I am aware of three different hydraulic setups for the PC200-6 models that had different pumps and valves. Early machines had the LS valve cartridge mounted in the valve while later machines mounted the LS valve on the pump itself. Nice job of following the book and chasing lines out. I would also suggest checked the pilot lines for the straight travel valve as well. Good Luck
my serial number is A80771 PC220LC-6L today i am going to do some more tracing
According to my book you have the earlier version and the L after the 6 in the model number means the machine was built in Lexington, Kentucky. The LS valves for your machine I think are mounted in the valve block and not on the pumps. It has been a long time so I don't remember for sure. My book is the usual Komatsu with lousy illustration about where the cartridges are but I seem to remember having a bunch of trouble on the later machines where the LS cartridges were on the pump. What I'm thinking about after you confirm all the lines are in the right places is to switch the LS cartridge valves and see if the problem switches pumps. It probably won't matter at that point if they are on the pumps or the valve blocks but I would like to know. John
based on what i see and also my book , the LS valves are on the same place as the TVC valves which is on the pump mounted as one unit . i do have two spare units lying somewhere around . i will do a Differential pressure test , try adjusting and if no change i will swap the ls valve on the problem side . i know it is not a control valve issue now because the problem did switch sides when i swapped main pump lines . i also did try adjusting the LS valve pressure blindly with no gauge a few turns up and a few turns down just to see if i get any change and it made very little difference ..
John , what is the best gauge combo to do the differential pressure test and any other tests for this machine ? i currently have a 10,000 psi , 3000 psi and 1500psi . i am about to buy some new gauges and just want to know what is usually used . and what length hoses would you guys use ?
I have four 6,000 PSI, two 1,000 PSI and two 600 PSI gauges. My hoses are ten foot long with #4 JIC female swivel ends that I can adapt to just about anything. All the gauges are the same make to try to keep them consistent between each other. They might be off but each one will be off by the same amount and read the same. Attached are some photos of my kit.
very nice . i got alot of ideas now
ok so today i think i had a little breakthrough , i was relieving one of the track circuits and then relieving the boom and the arm started creeping in just a little , just barely moving .. so this has to be a compensator issue .. i was also thinking that maybe the compensator for one of the tracks might be bad and this is why when i relieve the left track the bad compensator makes the other side build pressure or seem to / tries to move just like the arm . to confirm this i will raise the side i think has a bad compensator and relieve the other side and look for movement ? I think that LS pressure is leaking somewhere or being by-passed to the tank .. Maybe someone can tell me more about these compensator issues ? what to look for ? how bad will these compensators affect my machine ? I did do some checking around today i did get the two pumps to be somewhat balanced. both pumps / tracks at max pressure currently (200kgcm) and engine speed remains at 2250 rpm for both tracks respectively . both tracks build the same pressure now .. The arm is slow but when relieved it builds 330kg/cm2 boom is slow but builds 330kg/cm2 bucket is slow but builds 330kg/cm2 swing builds around 260-280kg/cm2 both tracks on both directions build 190-200 kg/cm2 all of these were done with the pumps split .. it swings faster with them merged because i guess more flow ..
Are you measuring the track pressures with the tracks locked up. I carry a pin in the truck that will fit between a couple of sprocket teeth and lock against the machine track frame. You should get max relief at that point. The other way to lock the track was to dog a bucket tooth in between a bar on the track pad. Max travel pressure was above the implement pressures. Travel is supposed to work on the high side of the two stage relief. I seem to recall the back side pressure as being normal on the early serial number machines. A bad compensator will just not let the pump ramp up because the LS pressure is being leaked off to the tank. It sounds to me like you can ramp up the TVCs for both pumps until your engine drops about 150 RPM with both pumps relieved on boom up with the swing brake set.
ok i will try this .. so one bad compensator can cause everything to slow down drastically ? also what seals do the tvc - ls valves (the pump mounted valves) contain that go bad and cause problems ? i read this somewhere about those seals but the post did not have much detail on this .. what happens when these seals go bad ? where are they located ?
I've never had seals in the pump mounted valve go bad. I have had the LS relief valve cartridge go bad and dump the LS pressure. I've been looking at the schematic concerning your question about opposite valve pressure. There are sub unload valves on each end. Have you checked differential pressure yet?
no i havent . maybe this weekend i will get time to do this .. no more info on compensation valve seal failure and also remedies ? also with the LS relief valve catridge failure was the remedy just a seal over ? or a full replacement ?
It's a cone and seat type cartridge. The cone gets a groove worn to one side and it leaks all the time. Back then it was about $80 for a new cartridge so it was generally worth the risk of it not being the problem. The dealers mostly just replaced all the compensators if there was a problem. Usually it fixed an issue but sometimes not and a problem like what you have would inflame all the participants. Take on out when you get the chance and see what is inside. At this point you have nothing to lose.
i will change the LS relief valve and see if i get any change ... and also check to see if i can get a set of new pressure compensators for this machine .. what i noticed today and i think this is something that is important .. i never took my unload pressure into thought.. my unload pressure at high idle is 100kg/cm2 .. book says around 40 .. could this be an issue causing my problems ? it seems the unload valve is connected to the LS circuit .. also noticed that any time i try to relieve or use any of the functions on the rear pump (pumps divided) the front pump seems to build a small amount of pressure .. 140-150 max .. also maybe related to this if i raise any one of the tracks off the ground and i operate the lever to test speed it is slowish . but . gets alot faster if i move the boom up or arm in lever slightly .. if the track is on the ground and i try to turn the machine with the track it does not move it, it just holds a pressure of about 200kg/cm2 on weaker track (rear pump) but if i move the arm in lever slightly the pressure goes up and down up and down and the track jerks and turns the machine whilst jerking .. the pump and engine gets loaded and unloaded really quick all in time with the jerks .. this does not happen with the other track but this one usually builds up to 250kg/cm2 ... i am yet to get more than 250kg/cm2 out of any of my tracks . i have tried locking the track with a metal pin and i did not get any change in relief pressure ..
It kind of sounds like you have most things narrowed down to the travel circuits. I don't recall if you said anything earlier but did you check case drain on that motor? I think I would make sure the swivel and both travel motors are not bypassing before you check the differential pressures if you haven't already done that. As I recall the circuit reliefs for the travel motors are in the motors. You might try to swap a relief from one motor to the other and see if it changes sides. I know you are thinking hard about what is going on. Try to step back for a bit. Just list all the issues you have noticed and then wait some time before you start doing the testing again. Your mind will work on the problems without you knowing about it. Things might clear up a bit when you get back on the project.
Thanks alot for the advice i am going to try swapping the travel reliefs . i dont think the case drain is high but i will check this . is there an easy way to do this ? do my strangely high unload pressures mean anything ?
To check the case drains you unhook and cap the pump side hose. Attach another hose to the motor side and run it into a bucket. Lock up the track with the pin again and try turning the track. I don't recall the amount they gave in the book but in my experience it should be less than half a gallon in a minute running into the bucket. If the motors check out the easiest way to check the swivel is to pull it apart and inspect the seals. If the barrel comes off the center easy then it needs seals. Don't know about the unload pressures as it isn't something I've ever checked before.
Does anyone know what a High unload pressure mean ? Komatsu Pc220Lc-6L Just experiencing some issues and i want to know if this can be a cause ? the book says 30-40 kg/cm2 and i am getting 100
Thanks alot John . i will do these tests as soon as i can .
has anyone ever replaced swivel seals on this machine ? i am ordering a seal kit from Plant parts . never done this before so any advice will be helpful . does it pull straight out when hoses are removed ? do all orings and seals go into the barrel ? is it necessary to have the rotor or shaft chromed ? http://www.komatsupartsbook.com/#?k=!0!1!6384!283!295 you can see breakdown of parts and names here
These are actually the easiest swivel to repack that I've ever dealt with. Remove the hoses, tie the case drain hose up higher that the oil in the reservoir, pull the pin on the stay rod, pull the bolts out of the top cap, remove the snap ring and pull the barrel off the center. The center stays in place and the rings go inside the barrel. You have to work a bit to get the new rings in and when you reinstall the barrel you have to make sure the eye is lined up well with the stay rod hole. A high lift jack works pretty well for pushing the barrel down over the seals. If you don't have that I've used a block of wood and a big hammer or weight to tap the barrel down into place. Never had one wear a groove in the center that would require chrome.