Piston/barrel dramas

[merv]

Looks like its totally been overheated which could explain the odd scalloping at the end of the stroke while the piston kind of dwells there allowing a far more localised heat buildup. Maybe it just plain melted. Now just figure out why? Oil problem? While maybe clearances were still big enough to prevent seizing.

[SS90]

Are you sure about that.

As it seems your emphatic diagnosis of cylinder/liner distortion was a bit off the mark......

That's only your opinion.

[SS90]

How many 250GP races did you do at National level?

That's the thing Warwick.... Even if I had only had one little lap, once... It would still be one lap more than these three.

[Gigglebutton]

Most of the posts on here were from guys relating something from their own experience and fair enough, but it looks like Bucketracer was the only one to lookup what the piston/cylinder liner manufacturers had to say about engine failures to confirm what he thought.

and raced at a national championship level in 125's and 250GP..... I am suitably qualified to question the accuracy of websites on this subject matter.

Only one ride!!!!!!! Ok it was only a little stretch.

I am not sure what the definition of “Masquerading as an Expert” is but exaggerating your qualifications has to be close.

Bucketracer may only be a School kid but has any one else noticed, he doesn’t have to BlowHard and lets the quality of his posts do the talking for him.

[Latte]

The wear doesn't look quite like circlip damage (at least not solely circlip damage) comparing the OP's pics and the pics supplied by BucketRacer.

Is it possible there's a lot of heat buildup coming from the little end / gudgeon area (maybe lack of oil, little end failure?). This is causing the piston to overheat around the gudgeon (as shown by the pitting/melting on the piston around the gudgeon openings) , which would have let the circlip loose.

This could also explain the wear on the barrel as the piston spends more time at TDC and BDC, causing the heat coming from the piston sides being focussed at these 2 points? I notice the damage on the barrel at these points matches the shape of the gudgeon opening.

Unfortunately I dont have years of building experience, or web pages to backup my theory...

[SS90]

Most of the posts on here were from guys relating something from their own experience and fair enough, but it looks like Bucketracer was the only one to lookup what the piston/cylinder liner manufacturers had to say about engine failures to confirm what he thought.



Only one ride!!!!!!!

Bucketracer may only be a School kid.....

I was being facetious.... I race 250's for 2 years (I owned 2 of them actually) and 125' for 4 years.

As a timely side note, there is a sticky in the title page of this thread informing all in sundry that this thread is to be kept clear of childish waffle...... Could you please bear that in mind in future post on here?
Thanks.

[jellywrestler]

The wear doesn't look quite like circlip damage (at least not solely circlip damage) comparing the OP's pics and the pics supplied by BucketRacer.

the difference is in the design of the piston.
The one bucket racer supplied has very little of the piston cutaway around the gudgeon pin area, whereas mine has quite a bit of releif there, the same shape of the barrell markings.
I will do a couple of piccies later today or so to show more of the piston

[Crasherfromwayback]

How many 250GP races did you do at National level?

And who is he anyway!!!

[Gigglebutton]

As a timely side note, there is a sticky in the title page of this thread informing all in sundry that this thread is to be kept clear of childish waffle...... Could you please bear that in mind in future post on here? Thanks.

SS90, looking back over your posts, it does look like your inner child was getting a bit carried away, maybe you should delete a few.

Maybe it just plain melted. Now to just figure out why?

Bucket in his posts suggested that the marks are not from the pin itself as its still retained but a piece of debris or part of a circlip has been rattling around, this typically leaves the piston looking melted in the pin area and the marks on the cylinder are more pronounced top and bottom as this is where the debris slam to a stop and both sides of the bore are marked because the offending piece of debri can pass from side to side through the hollow piston pin.

When the problem is traped debris, the marks on the bore match the cutouts in the piston and limited to the piston pin travel, his posts and links are worth a look.

This so called "melting" of the piston which is actually erosion by debri rattling around the pin area and the causes is also described by the piston manufactures in the links Bucketracer posted, I have read through them.

Jellywrestler has already ruled out there being a problem with the sleeve/cylinder so talk about sleeve machining faults and torque plates is irrelevant, the new photos will be interesting, hopefully front, back and both sides of the piston and a close look at the circlips.

Trapped debri could also be a piece of ring broken off during refitting of the cylinder, maybe a look in the sump may be in order as any trapped debri may have fallen in there when the cylinder was taken off.

[husaberg]

Are you sure about that.

As it seems your emphatic diagnosis of cylinder/liner distortion was a bit off the mark......

Well spotted Bucket racer
But I think SS90 is in more than his usual/unusual state of confusion. We should probably cut him a little slack as he is obviously not well.
Has anyone told him its not a scooter!!!
Although I suppose he has now kind of figured that out for himself finally.
As he as now gone on to the mopeds hence his furious backpedaling!!!!!!

[Latte]

Keep it on topic girls, this is actually an interesting thread

Interesting point about the damage, it does resemble a triple clamp where the keys have been banging against it for yeats and years, so it could be something rattling around in the side gap of the piston, instead of melting/heat.

Is it odd that both sides have the same wear? WOuld it be 2 seperate pieces, one on each side, or a single piece of debris travelling through the gudgeon? Would there be damage any damage on the inside of the gudgeon? (obviously harder material, but would be some evidence right?).

[SS90]

Is it odd that both sides have the same wear? WOuld it be 2 seperate pieces, one on each side, or a single piece of debris travelling through the gudgeon? Would there be damage any damage on the inside of the gudgeon? (obviously harder material, but would be some evidence right?).

Granted, but from real world experiance, my opinion is that When a cirlip comes adrift (as has been suggested) it, more often than not quite quickly ends up lodged between the piston and liner, leaving the offending item jammed in place, rather than the somewhat miraculous situation where it rattles between the two points, seemingly Perfectly in rhythm, leaving even marks at TDC and BDC.

The situation offered by others has put forward as being caused by a bent rod... My question would be, is the rod bent???

[Latte]

Granted, but from real world experiance, my opinion is that When a cirlip comes adrift (as has been suggested) it, more often than not quite quickly ends up lodged between the piston and liner, leaving the offending item jammed in place, rather than the somewhat miraculous situation where it rattles between the two points, seemingly Perfectly in rhythm, leaving even marks at TDC and BDC.

The situation offered by others has put forward as being caused by a bent rod... My question would be, is the rod bent???

Yes that's what I was questioning (as well as the damage on both side of the piston).

[husaberg]

Yes that's what I was questioning (as well as the damage on both side of the piston).

The engine damage has been sustained in only 285 miles. I doubt there is a single scenario relating to the failure but more likely a combination all of the things brought up thus far have come into play. All too often people go in search of a smoking gun when there more likely may have been more factors in play. Who built the engine,How come the engine was rebuilt, had it failed before the rebuild. Diagnosing an engine failure through pics is a little on the hard side like trying to tune a carb over the telephone. Vincent twins sure aren't that common . I do remember there being something weird/unusual in the crank float settings or such like on these engines I can remember what but it was unusual Just checked the notes- that is for the prewar singles and twins sorry.Not that it has anything to do with this the rods can also off course be twisted and the little end bush can be out of square too.From memory the Vincent twins consumed huge man hours in building them esp later on as the tooling became worn. I believe it was one of the reasons the company went broke.They were probably the most beautiful engine ever built,In one of the most technologically advanced designs for there time.The one think that struck me abot them the first time I ever got to see and hear one in the flrsh is how rately they were a lot going inside I guess lots af gears and all alloy which was rare at the time. Where's Phil (Irving)when you need him. Is Dick Hurdelman still around welly. let him have a look at it.

Jelly one of the clips had come out but that was after most of the damage had occurred as there's only light scuffing. Basically I suspect the faults occurred and started to melt around the clip to release it, also these piccies are of both sides of the top of the bore, the bottom is same or worserer...
I've yet to take the front barrell off to check the piston but the bore looks OK and compression check was cool.
New made piston by OMEGA, good reputation I believe New made liner/sleeve.
Ring gaps checked? Your guess is as good as mine. I didn't rebuild this engine and have already found quite a number of simple faults with it so can't rule it out at all, of course I can't just say that'll be it and rebuild it only to find something else.
F5 Dave liner 3.67 thick, plenty thick enough i reckon

On a short search I found this no smoking gun but relevent to the Vincent and probably other engines to.

Maughan & Sons
Vincent precision engineers
and spares manufacturer
Vincent engine barrels reboring and relining
A common thing with Vincent barrels, is that they often lose the fit between the cylinder liner and cylinder muff. There’s supposed to a 5-6 thou interference fit to ensure that the liner is snug and secure; in other words, the cylinder liner needs to have a cylinder bore 5-6 thou undersize. If the bore is too large, the liner will become loose and the clearance will be taken up by burnt engine coke.
This layer of coke, between the cylinder liner and the muff (cylinder) holds in the heat, which can result in a seized engine.
Incoming cylinders needing work are generally heated in an oven until the liner drops out. Nine times out of ten a lot of black coke comes out with it. We clean up and machine the cylinder bore, then fit an oversize liner with the correct bore size for a standard piston. Liners are made of spun cast iron, incidentally.
The final job is to hone the cylinders to finished size. This is handled by Steve who always hones the bore to near exact tolerance, and then leaves the cylinder overnight to complete in the morning. The reason for this is that things settle, not least steel. The liner protrudes a few inches from the bottom of the barrel, and this is unsupported. So it can “relax” after honing. If it does, you could end up with a piston nipping up during running-in (or even later). So the final honing is a two stage process.
This would be less of an issue in an age of less exacting tolerances. But modern machining and materials allows us to be more exacting, which has its own demands. And with pistons now running a 2-3 thou clearance, instead of 4-5 thou, you can’t afford to be sloppy

Below is an exagerated bent rod diagram

[Chambers]

Interesting thread.

I have read this right through from the begining including the links, but why people keep guessing when they could read what the big piston manufactureres have to say about this type of engine failure beats me, like you flick through their piston failure manuals untill you find a picture matching the failed piston and see what the piston manufacturers have to say about it, its not very hard.

Page 57 discribes what happens and lists the causes http://www.boosttown.com/engine/piston_damage.pdf

Granted, but from real world experiance, my opinion is that When a cirlip comes adrift (as has been suggested) it, more often than not quite quickly ends up lodged between the piston and liner, leaving the offending item jammed in place, rather than the somewhat miraculous situation where it rattles between the two points, seemingly Perfectly in rhythm, leaving even marks at TDC and BDC.

The situation offered by others has put forward as being caused by a bent rod... My question would be, is the rod bent???

Maybe the offending item could get jammed in place, seems sensible, but as for a miraculous situation, where it rattles between two points.

Well that is exactly what can happen according to MAHLE, AE Piston and MSI Motors as discribed in their engine failure manuals.

Now who is likely to know what they are talking about?.......

The piston manufactures, or the real life experience of someone who exaggerates his CV. its a hard one.

A bent rod is one of the miss alignment possibilities that can hammer the piston pin into the circlip until it shatters or is dislodged and was suggested by Bucketracer as the most likely cause. As the piston was recently changed the rod could have been bent from rough handling.

And if the whole motor has been apart there are other possibilities like excessive crank float, misaligned replacement little end etc.

No doubt qualified people know this, and its OK to ask "is the rod bent???" smarter to be able to suggest an easy way to check.

Signs of a bent rod or other alignment problems are diagonal wear marks across the piston skirt.

Yes that's what I was questioning (as well as the damage on both side of the piston).

This page talks about broken pieces of clip crossing to the other side of the piston .

Hopefully Jelly Wrestlers new photos and investigations will tell us more.