I have a Kubota v1505 in a mini ex that I’ve been working on. It began blowing smoke out the breather tube then after idling for 30 minutes it started to blow heavy smoke and loose all power, then had zero compression. I replaced the piston rings, head gaskets and glow plugs. I can’t for the life of me get it to fire off, even off a shot of ether. I bled the fuel system, I know kubotas can be a pain but this is the worst. It was hard starting prior to the total loss of compression. Cylinder walls and pistons looked good when I did the rings. I also checked the electric fuel shut off on the pump and it’s working. Any thoughts to get it to run?
Did you check the spark plugs? Just kidding. Have you tested compression after the rebuild?
I don’t have an adapter that fits the injector thread
I just ordered one, it’ll be here Monday! I’m hoping that’s not it with the new rings and head gasket but you never know.
Why did it loose compression so fast? Did you dunny brush (deglaze) the cylinders? Did you check ring gap? Piston to cylinder clearances?
I was welding on a thumb and had it idling when I was working, I looked back and it was smoking out the driveway. I thought it was on fire but it lose all power then wouldn’t restart. I did not brush it, I just checked the walls for scoring all seemed good. I didnt check ring gap either…
What colour was the smoke? Blue- oil White- coolant or raw diesel Black- over fueling diesel Where was the earth clamp on the machine when welding?
^
Yup had the ground on when welding. Boy it’s hard to remember the color, I panicked and drove it out a few feet out of the shop, I want to say white that turned black
air.
Would not deglazing the cylinders cause low compression? It had zero compression before I tore it apart
Do you remember where the earth clamp was? The damage current can do is amazing. Always connect clamp directly to the components being welded with paint removed. The cylinder wall cant be glazed or polished. The rings wont seal. Ring gap is important to measure. It may of had an oversized pistons put in previously.
I had the ground clamp right on the thumb less than a foot away from the welds. I have a feeling I’m going to be removing the pistons and deglazing the cylinders and checking the ring gap. The piston had STD stamped in them and I ordered std rings so hopefully they were good. I’m a backyard or farm mechanic as we say around here that only works on my own farm machinery and trucks
If compression is that low bypassing rings--with oil fill cap removed it should be a major huff of air. Chrome rings need a honed cylinder wall, old cast rings will seat on a glazed bore. Are the valves set correctly to firing order. Are the valves opening at the correct valve timing.
You can definitely hear the air and the crank case has smoke in it when turning over after the engine work. Valves are set to 8 thousands
Maybe its spun a key on the crank or something to put timing out. Pull glow plugs and rocker cover and check timing. Wind crank over until no.4 rockers overlap. Timing mark should line up on front pully and piston should be at top of stroke.
If there is smoke in the crankcase, you have a major problem with the overhaul. Did you stagger the piston ring gaps when you put the rings on the pistons ? Even if the timing is off there should not be any smoke in the crankcase. The new head gasket could be your problem. Did you have the valves ground and have the head magnafluxed ? Something bad happened before you overhauled it. Engines don't go from a running condition to no compression on a restart. New piston rings aren't going to fix it. IMHO
Kubota engines are famous for wavy liners. New rings on wavy liners will not work. By the time they seat…..if they even can, the ring gap will be too large and cause compression loss. You are dealing with compression loss before it even runs.
I did stager the rings. I’ll compression test it Tuesday when the adapters come. I didn’t get the head serviced, I checked with a straight edge and feeler gauges and it was nice and flat
So stupid question. If you don’t have an adapter, how did you check compression the first time and know there was none?
When I would crank it over it was like I didn’t have any injectors in. Spun that quick and easily
I got impatient and pulled it apart knowing it needed it anyhow. These are the pics of the cylinder walls. I can’t feel anything with my finger nail, looks shiny and glazed for sure with some marks. Picking up a home tomorrow morning before work. Do you recommend a ball or stone hone?
They look like they were honed with a grinder by someone. Have you miked them to see if they have much taper from wear ?
Lol they don’t look fresh that’s for sure. I havnt miked them, I don’t have a bore mike
Stone hone--Looks like cylinders were emery papered, part of the carbon soot line above top ring is still there in some places. * Some photos of piston skirts.
If you dont have a micrometer, take the rings off the piston and put top ring in cylinder. Then use piston to push ring down evenly. Use feeler guages to measure ring gap at multiple locations. This will give you an rough indication of wear in cylinders. How long have you owned the machine? I think someone has already been in there recently and its all bad.
YIKES! Looks like #3 has a vertical gauld
All 4 cyclindars have vertical darker marks. I’ll check them with the ring and feeler gauges tomorrow! I bought the machine 2 weeks ago, started doing maintenance and paint on it, then the motor went out. The guy before me said they did a head gasket
Sorry to hear that. My guess. They overheated the engine. Pulled head and noticed cylinders had picked up. Honed bores, put oversized rings in. Filled with 50w engine oil and sold it to you.
He warned me it was hard starting and I noticed the blow by so that makes sense. Hopefully honing the cylinders fixed my issue
Good luck on honing the cylinders to stop the blowby. Ain't gonna happen. It needs new pistons and whatever you need to do to eliminate those nasty cylinder walls.
That block needs bored not honed
A hard starting diesel engine quite often indicates low compression, especially on one with an unknown history. As said, you’re in for a rebuild. A decent cylinder will have no visible vertical scratches, let alone all of them. That many scratches can be caused by carbon buildup on the pistons. Are you sure you didn’t have tight valve lash before you tore it apart? As Truck Shop said, show us some pictures of the pistons- tops and especially the sides(skirts and ring grooves)
Ok-----this is where issues come from trying to answer OP questions no matter the thread. Had all of info been dumped out at first this would have taken about 4 replies to answer. * Strip it, have it machined, cleaned, engine rebuild 101.
That Kubota has press in sleeves that have to be finish honed. Thats why it's almost impossible to throw new rings in and it actually work.
Yes--the correct way done with a wet tank hone.
Actually no sleeves at all. parent bore block. You can bore to .5mm oversize, unless that is done already, or if that doesnt get it perfect, or if no oversize pistons are available. Then you will need to bore out and install repair sleeves back to std. Either way will need finish hone
Got them all honed, I used a feeler gauge on the piston ring in the cylinder like you guys suggested and it was well within specs. Got it back together and after a tremendous amount of bleeding fuel she fired up! The compression tester I ordered got pushed back so I didn’t get a number but she’s running again. Thanks for the suggestions everyone.
Glad to hear. And thanks for returning to tell us the results.
What did you end up honing them with?
An accurate measurement of a cylinder wall cannot be achieved by measuring the end gap of a piston ring inserted inserted in the bore. The reason being you don't know what that particular piston ring end gap is in a NEW cylinder with a known inside diameter. Worn bores have to be measured at the top and bottom to determine if the taper in it is acceptable to put new rings in it. Many times I had to file piston ring ends to get the correct end gap in new cylinder sleeves. I noticed in your photo that the ridges in those cylinders hadn't been reamed. I hope they were removed before you reassembled the engine.
Correct---but as usual all that matters is it runs--for now, never mind how much oil it uses. A real important aspect of honing is getting the correct angle of crosshatch, rarely does that happen unless done in a controlled wet tank machine.
Yes and also very important to remove all the honing grit from the cylinders until a clean, oiled white rag can be rubbed heavily around the cyl and comes out without any grey residue on it
You can wash till the cows some home--it will still turn a white rag gray. Just look at it as though it is Bon Ami. * The engine most critical about cylinder crosshatch being correct=======3208.
I noticed in your photo that the ridges in those cylinders hadn't been reamed. I hope they were removed before you reassembled the engine. Just bevel the top ring on a grinder, problem solved. Joe H
That makes sense on 3200 series engines, especially when only 2 ring pistons are fitted. Glad the OP has it running. Hopefully it will break in properly.
I used a 3 stone hone