Stuck piston

[John northcott]

Hi Guys. I have a David Brown tractor with a new set of pistons to put in. It had a warped head which blew the head gasket allowing water into the combustion chamber, which pressured the piston on number two and broke the skirt off. Pistons and cylinders are relatively new having only done 500 hours, so there is no wear ring on the top of cylinders. Pistons in 1,2 and 3 came out easily through the top of block after unbolting caps. Number 4 jams solid when the piston comes 5/8 inch above block top and won't budge. It's solid. Hitting it with a 4 pound hammer bounces back. It runs perfectly up and down bore but wont come out top. Wonder if the skirt is deformed due to water in combustion chamber when head gasket leaked. Thinking of using a 6 ton jack and a 1 inch rod to force it out, maybe forcing cylinder out too. Any thoughts.
John

[anonymous-user]

Can you remove the block and drive it through the bottom of it? I’d be wary of forcing it out the top not knowing if the skirt is knackered and how badly it’ll pick up in the bore?

[anonymous-user]

Nanook said:

If the skirt was deformed or warped, it wouldn't slide easily up and down the bore either though?

Fair point. Is the top of the bore in much better condition, can you clean it up if so?

[TooMany2cvs]

You must have the sump off, to have undone the caps. What can you see from below?

What's likely to be trying to enter the bore when the piston stops? Could it be a bent rod from hydrolocking?

[John northcott]

Thanks guys for the thoughts. It may be possible to see the bottom of the piston skirt from below. I do have the sump off obviously to remove caps. The conrod is moving freely at point where the piston sticks, so I don't think its deformed being a diesel its very strong. There is some carbon around the top of the bore, so I will clean it off and oil it before trying again. I don't want to take the block out as I would have to take the tractor in half. Damage to the bore is less of an issue as the cylinder is a replaceable sleeve. Thanks guys

[TooMany2cvs]

John northcott said:

I don't want to take the block out as I would have to take the tractor in half.

Can you remove the crank in situ?

[PAUL500]

I take it the pistons went in from below when the rebuild was done, seems the top of the sleeve warped at the time and it was not realised at rebuild.

What you propose may bring the sleeve out along with the piston, but you risk damaging the piston in the process.

Is it expensive for a new sleeve and piston if you do go that route, other than dropping the crank and removing it that way instead?.

[John northcott]

Thanks for the thoughts. The piston is to be replaced anyway so it doesn't matter about destroying it. One suggestion is to smash the piston to get it out. The bore may be out of whack, but the piston does come up 15 mm above the block before jamming. To remove the crank I would have to remove the flywheel, clutch and gearbox, pulling tractor in half. I will try cleaning the bore top of carbon and use oil to lubricate. I will use 6 ton jack and heavy rod to push it up. Hope it doesn't crack block. Cylinder is not too expensive to replace, but block is a hassle to remove as described, if I crack it. The joys of having motors!!!

[Benrad]

I'd say you need to replace the cylinder liner anyway, it could have been that that caused the head gasket failure. Can you remove the liner with the piston still ok it, to avoid the jack method and other potential damage you could cause?

[John northcott]

Good point. I'll try it

[John northcott]

Does anyone know how the cylinder liner comes out? I have taken out a wet liner with an o ring in bottom but not a dry liner. Do they press in? By the way, the liner looks ok from the top, apart from the usual carbon buildup. There is no rim on it from wear. I''l have a go tomorrow and let you know. Thanks

[Mignon]

Regardless of what you say, if the piston won't slide through the top of the bore but is fine below that then there must be something different about the top of the bore. A wear lip a ring is getting stuck on, carbon buildup. Clean it properly with a fine oilstone lubricated with paraffin or diesel. If there's a significant wear lip you haven't noticed yet it might need to be scraped off.

[Mignon]

yonex said:

Can you remove the block and drive it through the bottom of it? I’d be wary of forcing it out the top not knowing if the skirt is knackered and how badly it’ll pick up in the bore?

If you'd ever actually built an engine you'd know pistons don't come out through the bottom of bores. The crank webs are in the way.

[TooMany2cvs]

Mignon said:

If you'd ever actually built an engine you'd know pistons don't come out through the bottom of bores. The crank webs are in the way.

Depends whether the crank's there or not, doesn't it?

[anonymous-user]

Mignon said:

If you'd ever actually built an engine you'd know pistons don't come out through the bottom of bores. The crank webs are in the way.

Good point. The only siezed pistons I have had to hammer out were on GP bikes, which are slightly different. Thanks for the insult though

[InitialDave]

Mignon said:

If you'd ever actually built an engine you'd know pistons don't come out through the bottom of bores. The crank webs are in the way.

He posted his (correct and valid) suggestion before the OP explained why he didn't want to take that approach. Don't be a knob.

OP, have you measured the bore to see if it's deformed/tapered as others have suggested?

You're sure it's the piston catching in the bore, not the bottom end of the rod catching on something at the other end?

Edited by InitialDave on Thursday 13th September 12:27

[Mignon]

TooMany2cvs said:

Depends whether the crank's there or not, doesn't it?

No. The webs are the buttresses in the block that support the crank bearing housings and pistons can't pass by those. No car or truck engine can get the pistons in through the bottom of the block.

[Mignon]

InitialDave said:

He posted his (correct and valid) suggestion before the OP explained why he didn't want to take that approach. Don't be a knob.

No, it was an impossible solution. I suggest you learn more about engines.

[John northcott]

I did check the conrod to make sure it wasn't jamming but I'll recheck it. Good point about the top of the bore having an obstruction. It does seem to be catching on the top compression ring. I'll measure it after I clean the carbon and see if one of the other pistons will go down the bore upside down when the stuck piston is at the bottom of the stroke. It may have been bumped putting the head on a while back and have a burr on it from damage. I'll try the piston trick from the top and do some filing with a round file to remove any burring on the top lip. Top compression ring doesn't reach the rim when its operating so small file marks won't do any noticeable bad effects. Thanks

[Mignon]

Here is a photo of the underside of an engine block. This is why pistons can't come out through the bottom of the bores. The main bearing housings overlap the bores. Now do try to stop being dumbasses.