Uh Oh Part 2!

[Cameron 16]

Ah, yeah of course I forgot it was freshly built!

 

No it shouldn't be rusty in there, and you'll probably find the seals are in pretty good nick.

[Dave_McC 0]

The liner seats were machined to remove all corrosion and the seals were smeared with grease when fitted (QEP's recommendation to prevent corrosion) so there shouldn't be any problems. Make sure you mark which way round the liner is fitted.

 

I don't know which location the piston with the broken ring was fitted to.

 

Dave

[Jrod 7]

Well I removed all the pistons tonight. They all look fine with not much difference between them all to my untrained eye.

 

Here is the one that was actually moving though (number 4)

 

 

The piston ring doesnt look broken to me...

 

Edit: resized pics as they were huge (and still rubbish quality! )

Edited October 28, 2009 by Jrod

[Galifrey 1]

That piston looks like it has been siezed.

[Jrod 7]

...

 

The liner looks totally fine to me (no marks etc)

[Galifrey 1]

...

 

The liner looks totally fine to me (no marks etc)

 

Well the piston doesn't look great mate, looks like someone has take 40 grit to it! I don't think that is what has happened, but that piston does look worn around the crown edge.

 

Entirely possible the picture is making it look worse than it is, but loads of play in the liner, worn looking piston, just saying what I see.

Edited October 28, 2009 by Galifrey

[Jrod 7]

It doesnt feel smooth, quite rough.

 

Not sure what pistons should be like though as I said before this is the first time I've ever removed one!

[Dave_McC 0]

Piston certainly didn't look like that when the engine was built. From the pic and your previous video of the piston moving about in the liner, it looks like the piston has been rocking about the little end and has worn itself away. However I would have expected to see wear on that side of the liner (and also on the opposite side of the piston but at the bottom).

 

There was no noticeable play of the piston in the liner when built. Also seems strange it is only that piston?

 

Dave

[Galifrey 1]

Piston certainly didn't look like that when the engine was built. From the pic and your previous video of the piston moving about in the liner, it looks like the piston has been rocking about the little end and has worn itself away. However I would have expected to see wear on that side of the liner (and also on the opposite side of the piston but at the bottom).

 

There was no noticeable play of the piston in the liner when built. Also seems strange it is only that piston?

 

Dave

 

The piston moves in that direction anyway on a little end, the only reason it would rock on the little end more than normal is out of tolerance with the liner. I think that has dried/overheated around the crown and partially siezed, the ally on the bore can be scraped back off by the rings if the engine is run afterwards.

 

That then left enough tolerance on the bore for it to move.

 

Do you have another piston you can test fit in the liner? Maybe use one of the others to check tolerance on the liner? Then get the piston mic'd up to check for size?

[Cameron 16]

I think you've pretty much nailed it there Galifrey.

[Galifrey 1]

I think you've pretty much nailed it there Galifrey.

 

 

Well the reason I went for that is the sudden way it got noisy. If it had been out of tolerance before the "event" then you would have had some bad piston slap from day 1

[Dave_McC 0]

So what would cause a single piston crown to dry / overheat? Overheat I'd normally associate with running lean - but the injectors were all cleaned / flow checked so a single cylinder should not run any hotter than the others.

[Galifrey 1]

So what would cause a single piston crown to dry / overheat? Overheat I'd normally associate with running lean - but the injectors were all cleaned / flow checked so a single cylinder should not run any hotter than the others.

 

 

Manifold airleak would be my no1 guess

[Jrod 7]

When the head gasket went I used Genuine pug inlet manifold gaskets so not sure why it'd leak but I won't say it wasnt as I've no idea.

 

The problem I have now is replacing this piston and liner.

 

Dave do you know how much was removed from the top of the piston?

If not could I take one of the other pistons and a new one and get them to machine the same amount off? Also is it likely the liner is wrecked? Best to have this checked?

[Jrod 7]

Or could I replace them all and not bother machining them at all (depends how much was removed from the block I guess?)

[Jrod 7]

Ok excuse the poor pics again but these might help

 

Piston number 3:

Piston number 2:

Piston number 1:

 

Another problem I'm starting to realise now is my distinct lack of funds, I may have to SORN it and leave it for a few months as money is tight at the moment. I struggled to buy the car prior to selling my motorbike and as I've not sold that still and I've already spent too much for parts from when the tensioner came undone.

 

And just to show how bad my luck is heres a piston from my first motorbike.

Edited October 29, 2009 by Jrod

[Galifrey 1]

Those 3 look much better than the first.

 

Looks like you may get away with a single piston replacement.

[DrSarty 90 1 Cars]

As long as the new liner seats correctly, and you get the liner protrusion correct (0.003inch) and check the liner is square with the face, then I can't see any reason why you can't just replace this cylinder/piston combo complete.

 

Push through this and all will be well again. It was a mechanical failure brought on by something that was either done incorrectly or a part is/was faulty, most likely lubrication related in my mind.

 

You'll need to try and get to the root cause of the problem to ensure it doesn't happen again.

 

But once it's fixed, you'll be a smiling Pitcrew member again.

[craig_007 1]

Hi Mate,

 

I had much the same thing happen to my MI 16 engine,I was doing a track day at the time though.

 

Piston number 4(nearest timing belt) had partially seized to the liner,The piston rings were melted to the piston in places and my piston was badly scored on one side,The scores are similar to yours but mine were a hell of alot worse but I didn't have the bad knocking you have.

 

I removed the piston from the rod and noticed quite a bit of wear on the small end,Sandy from here reckoned that would be down to the heat that caused the piston problem to begin with,The wear on the small end is noticeable when you remove the piston,The small end will be woren through to the brass !!

 

I'm still not 100% sure what caused this but I'm thinking along the lines of oil temp was to high/coolant temp to high.

 

I have a set of high compression pistons/liners and rods(83.5mm omega) sitting about the garage that I could be tempted to part with but if your building on a budget maybe not.

 

When I rebuilt the engine I only changed one piston/rod and left the other 3 but I checked condition of smallends honed bores and renewed rings etc,I only changed the rod as the smallend had wear on it.

 

Craig

[Dave_McC 0]

Jordan

 

From memory you won't be able to replace all 4 without machining the pistons. I have a vague recollection it was about 1mm skimmed off the top of the piston crown. This was all because of the Mi bugbear of corrosion on the liner seats in the block - this required QEP to machine the seats in the block - which resulted in too little liner protrusion. They then decked the block and finally machined the liners for the correct protrusion.

 

Ideally the existing liner is still ok - personally I'd whip it out (it should come out easily - just mark which way round it goes) and get it checked. Get a replacement piston and get it machined to match the others.

 

Re the little end - if there is wear from memory you can just get the journal drilled out and a new brass bush inserted - if you can't get another rod. If you do get another rod, get the big end checked for ovality / wear - just to check it's not come from an engine that's spun a big end.

 

You should be able to sort for not too much money - from memory machining all 4 pistons was £40 and I paid £40 for a set of 4 pistons and rods.

 

Dave

[Jrod 7]

Thanks Dave,

 

The liner is out so I'll get it checked. Will get hold of some pistons and go from there.

[Jrod 7]

Slight problem, I don't know what size the current pistons are as its been machined off?

Edited October 30, 2009 by Jrod

[Cameron 16]

Can't you measure them?

[Jrod 7]

I guess so, not sure how much of a difference there is. Does anyone have the sizes for the different types so I know which ones I have?

[welshpug 1,657]

are you getting all 4 pistons and liners or just replacing one? just get matching ones to be sure either way is the best approach.

 

Piston Diameters measured 13mm up from lowest part of skirt were;

 

A - 82.963 to 82.977

B - 82.973 to 82.987

C - 82.983 to 82.997