Hi I have a d8h cat (46a24576) with which I have recently finished a rebuild on the motor. A few of you might have seen a previous thread of mine about a high oil pressure problem, this is a seemingly minor problem at the moment as I have recently had a world of trouble with this engine. The engine was a full rebuild in every sense, all bearings, pistons, liners, ground crank, etc. Ran the motor out of frame first, all good no leaks, then into the frame. Put the tractor to work, all good, heaps of power, no noises, ran beautifully, for a while. Then while working the engine, it loaded up and squeaked briefly. Sensing the problem instantly, went back to idle and the engine stalled. Within a few seconds I restarted the engine and white smoke coming out the breather. In disgust it was shut it down and left, the next day i ran it briefly back to the workshop. After a few conversations, I feared the worst, that a bearing had failed. After a snap decision I pulled the engine back out, and after much searching found the rear pump drive bearing had grabbed and spun. After deliberating, it was found to be my fault, I had machined up this bronze bearing myself (reasons I wont go into) and hadn't given enough clearance. It damaged the shaft, so shaft was ground undersize, and a new custom bronze bearing was made, with much more clearance (same as new cat bearing bought). The engine was put back in with the oil system reprimed. From start up the engine didn't sound right, unlike the first round. There was a rhythmic squeak which went up through the rpm range. First thing I checked was the pump drive, all good. Didn't like the situation but persisted to give it a run, only drove it a few hundred meters, when another issue occurred. It blew the guts clean out of a glow plug. On inspection the bulb of the plug had been burnt or broken off, as well as one other. These bulbs have gone into the engine, been crushed up and have been blown out. I know this, as there is peening on no.1 piston and signs of light peppering of debree, on the turbine of the turbo (no major damage there luckily). The manifolds and head ports were inspected and cleaned, new CAT plugs put in, and the engine was re run. Currently think that the glow plug issue was due to the cheap aftermarket plugs used, as the machine has been rerun and no trouble since. Now I still have this issue of this strange noise, made worse by the fact that the engine doesn't seem to perform, it definitely doesn't have the power that it did when i first put the engine in. Lately I have done a compression test, which seemed to be ok (400-450psi). Few final notes The noise gets worse when working The noise seems to be coming from the back of the motor Noise doesn't start till 10 to 20 sec after startup Seems to be fair bit of blowby coming out the breather when the engine is working, but compression seems good???????? The fuel pump, fuel and cam timing were never disturbed on the 2nd dismantle. Just about to do a stall test, maybe now a problem with converter, but was perfect on the first run???? Tearing my hair out, so any thoughts would be greatly appreciated
I have no idea, but bad turbocharger seals can lead to increased crankcase pressure under load, and it seems to align with your symptoms.
Can you remove the turbo and see if the noise stops , sudden drop in power could be the turbo , being all over it you would have noticed a hole in the exhaust manifold , sure way to lose HP
Just an off the wall idea on the turbo seals causing the blow by. How hard would it be to remove the drain line from the turbo an fab a temp drain, or maybe re-position the drain to dump oil into a five gallon bucket , then run it for a short time to see if the blow by changes? Just trying to separate systems to prove where it is coming from or not coming from. Another idea would be to supply air pressure to each cylinder one by one to see if one is leaking past the rings from damage from failed glow plug bits getting stuck someplace not good. Might have to do test with pistons at bottom dead center on the power stroke and back off exhaust valves to be sure they are not opening. Then listen for air in the crankcase.
Sure points to the turbo with all those symptoms you're describing.
Appreciate your thoughts but the turbo is brand new cat reco, only done hours work, it has always had oil flow from day one (checked), i pulled off the exhaust snail after the glow plugs **** themselves, and it looked and felt ok, i think it unlikely that seals would have failed, but it could explain the blow by and lack of power, i haven't tried running with turbo off yet, i might try it Exhaust manifold was replaced a few years before rebuild, it was remachined during rebuild, there's no cracks or leaks
Just thought if the turbo seals had failed, oil would leak into exhaust and produce white smoke, which there is none
I have had failed turbos behave normally at low loads and blow crankcase pressure at high loads. I don't know if it was RPM related or maybe drive pressure was enough to overcome the hot side seal but recon turbo fixed it.
Have seen a Cat reman turbo on a 7 G fail in the first 20mins, and it was all assembled by the Hastings Deering fitters so no cowboy stuff going on so it is possible to happen.
I know it doesn’t account for blowby but when you say rhythmic squeak I think of rocker arm to rocker shaft scoring . I’ve seen more than one engine put together with dry rockers cause squeaking even after they get oil pressure.
what should boost pressure be on this machine?
Boost pressure is 33 +/- 3" Hg at full load and speed. 29 +/- 3" Hg at torque converter stall speed Torque converter stall speed is 1056 rpm Readings w/o muffler. Compression test is not really recommended by Cat but 445-485 psi at cranking speed cold would be expected.
Appreciate the replys Did a stall test and is only doing 900rpm and boost is down a lot, don't trust the gauge much but it had 5psi at stall. Ran the engine without the turbo, blowby still the same, still had noise. It just wont blow smoke, so I then concentrated on the fuel system, checked fuel line, drained and checked filters, reprimed, still had stall at 900. So then i pulled the end of the pump off where the rack limiter is, stalled it again and the rack was limiting out (full fuel) ????, next i thought a lock nut on the fuel pump lifter might have come loose, so I checked, all tight, even pulled one plunger out and checked lifter setting, perfect ??????? Non of the fuel system was touched between its first (powerful) run and the second time the engine was put in Have just started hooking compressed air to cylinders, so far done cylinders no. 4,5,6. Have a hint at the problem as all three have air escaping out of exhaust manifold( yes, the valves were shut). Cannot think of any other way it would get through but though the exhaust valves. No. 6 was damaged by glow plug so that would be understandable and would have been the smoking gun, but the other undamaged two are leaking as well so I'm not so sure. Compression readings for 4,5,6 were 450,430 and 400psi respectively. Will finish air test tomorrow. Running out of moves, thinking of pulling the heads and checking the valves. Even if the compression is down a bit, I wouldn't have thought it would have a substantial effect on hp, it had more power when it was worn out (using lots of oil), so that's why I think it's the fuel, but non of the fuel system was changed, ( a conundrum), lack of the fuel doesn't explain blowby I know! Once again welcome any more thoughts
This has the possibility of outdoing the Steve Ahlgren thread. The heads were already off......correct? A squeaking noise is usually something that is running dry of lubrication.
Have you checked valve clearance?
Are you getting oil flow to the rocker arms/shaft? Rack setting should be 0.365" What have you got for fuel pressure, should be 32 +/- 7 psi.
yeah valve clearance was rechecked. Rockers have been checked. Ran with covers off oil running out each rocker I do appreciate those specs Old Magnet, is that rack setting the block distance off the pump body (hitting against the rack collar) ? I don't want to alter this setting, but might measure it just for interest Fuel pressure was checked a while ago but will check again
Yeah the heads were pulled in the second strip, before we found the problem, thought it might have been tight rings. I do agree, it does sound like something is running dry, but just haven't found any other evidence yet to back it up. The head gaskets were reused, which was based on advice at the time
Are you sure that the decompression system is not interfering with the valves seating correctly? Edit: I re-read your initial post. I am wondering about the possibility of a valve having been bent when the glow plug went through which is now not sealing, causing the blowby and low power.
Rack setting is fairly involved and requires special tooling but yes it references the center of the injection pump quadrant to the rack collar just coming in contact with the stop bar.
It’s an original electric start heads, so no decompression valves. I’m now thinking valve damage as well
Did run turbo drain into drum, I was still getting blow by out of breather, so at least I can now eliminate the turbo I think I will pull the heads tomorrow. Hopefully I find something definite
Back to glow plugs, what I have for reference material states to use a 1P7324 glow plug. Overall length is 117.5 mm, the element part is 23mm long and the tip diameter is 6mm.
Do you hear this noise more so on the left side of the motor if your sitting in the seat?
John check to see if you haven't mixed a fuel pipe between two cylinders, they will run but with less power and plenty of blow by. Bill
John,your thread is a heartbreaking read mate. I feel your pain. I'm no fitter,but I've owned 12 x D8 dozers in 30 years without going bankrupt and my gut is telling me,that engine is going to be needing the heads off sharpish,and the sump.
Just an update and closure on the matter. Tried a lot of different things to no avail, i eventually pulled both heads to reveal, two cracked heads on No1 and 6. These were brand new loaded heads, so my frustration was now even higher. It had also just started to melt the tops of those pistons I had been speaking too a lot of old school well qualified mechanics, with a mixed bag of responses. I got one more opinion from another respected (old cat) mechanic, with which i was asked, if i simply hadn't crossed over no.1 and 6 injector lines over on the pump? I had a abrupt response as i knew then and there, that this was my mistake. i hadn't been looking at the forum lately, but if i had (8k Bill) would probably have done the same, cheers! The plungers are next to each other on the pump, i think the lines got bent in the workshop while off, then with little trouble they were reassembled in the wrong order. As explained earlier, it ran alright but was down on power, had a funny noise and had increased blow by. I learnt the hard way but hopefully this will help others Thanks for all the help
Well, there you go.
john stewart, Sorry to hear of the damage but at least knowing the problem has been figured out has to be some comfort! Now if I could just figure out why this 20 year old brush cutter won't start.......good spark and compression and I had the carb apart once! Maybe if you could get the D8 running you could run it over so I'd try fixing something else!
Hell fire. I've got the buggers crossed in the past,but been lucky enough to get them quickly. This is a hard pill to swallow John. As to what you'll do next,the passage of time will help you make the desision
Yep been there and done all that, I too managed to catch it before it left the workshop. We all live and learn the hard and expensive way sometimes. cheers bill
just as a comment, whenever I pull off injection lines, I always leave the clamps on if at all possible and pull the whole clump off all as one or on some engines in two clumps. then there is less chance of mixing up lines. if the clamps are left tight, the lines should not move enough to get them mixed up. I've seen some god-awful messes when guys took all the lines off individually and then bent them all to hell to get them back on. then the clamps wouldn't fit so they left them off causing lines to rub and wear through