Project over my head is dead!! (edited) By Bashan (Read 4,680 times)

[noday]

I disagree with the conclusion of SE and moat above, no disrespect intended in any way.

I agree that the minor irregularities of the case opening is of no consequence and that a perfect fit is not needed.

What I think happened:

The opening was bored eccentric with respect to the studs. there is more metal between the stud holes and bore hole on the side opposite the cam chain passage.

the metal there is thicker than the corresponding space on the cylinder from stud hole to liner/skirt/sleeve.

because the liner has very thin metal in the skirt, the skirt deformed at assembly.

when you look at the bottom of the cylinder, ( in the first set of pics) you see that about half of the cylinder skirt is missing along with a big chunk of the piston side that goes up to the wrist pin hole in the piston.

It appears that the piston hit something and stopped (on a down stroke) and then was pulled apart, taking the missing cylinder skirt with it.

what I think the piston hit was a ridge in the cylinder wall caused by the eccentric opening in the case.

if the cylinder liner skirt had been thicker, it probably would have not seated/mated to the case without extreme force.

to be more certain of this proposed mechanism, more exam of the cylinder and piston is needed, along with measurements of the suspect area.

a retrieval and exam of the missing pieces of both the piston and cylinder skirt may give more light.

so I will leave my proposed theory up for critical discussion.

perhaps some one else sees something in the pictures that I do not and has a better explanation

[Alleyoop]

I agree with Noday,
The jug should have even support all the way around, it takes extreme heat and will deform if that caseing is not supporting it properly.
Alleyoop

[Moat]

Aug 7, 2012 15:44:28 GMT -6 noday said:

there is more metal between the stud holes and bore hole on the side opposite the cam chain passage.

Look closely - the R/H stud holes are bored larger to accommodate the the R/H stud's locating dowels, only installed on that side. Optical illusion... just looks that way.

Aug 7, 2012 15:44:28 GMT -6 noday said:

because the liner has very thin metal in the skirt, the skirt deformed at assembly.

How could the liner deform if it's not in contact with the case bore? Again... they are not meant to come into any significant contact - if they did, during assembly - the builder should have backed off and figured out why things were not fitting together properly.

He'll have to chime in here and describe if he had to force the cylinder onto the case.

[Random Hero]

I have had to replace the center part of the case before and when i put them all together they did not match up 100%. The jug fit in nice and i had no issues at all.

[noday]

to clarify what I was trying to say.

I am comparing the base of the cylinder to the case. all the pics are taken at different angles and some distortion is present. so one can not take measurements from the pics as there is no measured scale included with in the pics.

It looks like, when I compare distances, from cylinder base to case, that the case would impinge aginst the side of the cylinder skirt, when the cylinder was seated.

on the cam chain side, it did not.

I compared 2 pics. the cylinder base was flipped and rotated so that the same stud holes are in the same position in both pics

both are close to the same scale, from center stud hole to center stud hole, left side of the pics





even so, direct measurements are needed

perhaps this is just optical illusion

[Moat]

Aug 7, 2012 18:50:10 GMT -6 noday said:

to clarify what I was trying to say...

OK noday - I now see what you mean. The comparative clearances look quite close, but as you elude to - it's impossible to say, without careful measurement. And the case's threaded stud holes are clearly smaller diameter than the cylinder's stud pass-thru holes, so... hard to compare from here. You'd/we'd have to have been there, I guess...

But again, regardless - if the cylinder slipped easily into the case bore like it should (with clearance between liner and case), it's completely a non-issue. And, conversely, if the builder had to force it on - he should have pulled it back apart to find out why. Too late now.

[justbuggin]

i thank everyone for their thoughts on this it is IMO that the case was not machine right and that would cause the skirt of the cylinder to deform and that would cause the piston to break it could have slip in with no prblems and after warming up force the cylinder to deform as al and steel will expan at def. rates

[justbuggin]

still would like to see pics of a new case that is bored out correctly

[Moat]

Aug 7, 2012 21:46:11 GMT -6 justbuggin said:

it is IMO that the case was not machine right

I still don't understand how someone could come to that conclusion, with so little information presented.

In this re-posted pic below, note the relatively even offset/mis-match of the case bore halves - the LH side being higher than the right. Isn't it just as (err... more?) likely that the builder left out a case locating dowel pin, and the case halves torqued out of alignment under load?



There are plenty of unanswered possibilities behind this failure, and no reason to jump to conclusions yet, IMO.

[Deleted]

I do agree tho that the case was not machined properly! That with the thin cylinder walls is what caused this in my opinion

[Alleyoop]

Aug 8, 2012 11:32:56 GMT -6 Moat said:

Aug 7, 2012 21:46:11 GMT -6 justbuggin said:

it is IMO that the case was not machine right

I still don't understand how someone could come to that conclusion, with so little information presented.

In this re-posted pic below, note the relatively even offset/mis-match of the case bore halves - the LH side being higher than the right. Isn't it just as (err... more?) likely that the builder left out a case locating dowel pin, and the case halves torqued out of alignment under load?



There are plenty of unanswered possibilities behind this failure, and no reason to jump to conclusions yet, IMO.

Little contradiction there don't you think: the builder most likely left out a case locating pin. Maybe they did not come with alignment pins.

There is in no way anyone will really find the cause of the failure PERIOD. But one thing sticks out like a sore thumb and that is the markings on the case from the boreing and the very thin walls where pieces of the case broke off.
Alleyoop

[jct842]

In my opinion that gy6 case is just way too small to put that big of a piston in it and have any kind of reliability. The designers of the gy6 had no idea someone would take it up to 150cc much less to 200cc. If they did they surely would have spaced the 4 studs a lot further apart than they are. It would be so nice to find a case actually designed as a scaled up gy6 with enough meat to safely mount a 200 or 250cc barrel on with a scaled up crank and still be able to use as much of the old gy6 parts as possible. And maybe a finned crank case to allow better cooling and more oil capacity.

[Deleted]

Aug 8, 2012 13:06:39 GMT -6 jct842 said:

In my opinion that gy6 case is just way too small to put that big of a piston in it and have any kind of reliability. The designers of the gy6 had no idea someone would take it up to 150cc much less to 200cc. If they did they surely would have spaced the 4 studs a lot further apart than they are. It would be so nice to find a case actually designed as a scaled up gy6 with enough meat to safely mount a 200 or 250cc barrel on with a scaled up crank and still be able to use as much of the old gy6 parts as possible. And maybe a finned crank case to allow better cooling and more oil capacity.

There is. Taida Makes GY6 cases that can be bored up to 67mm but they are very expensive running about $500.00 + only thing is it is 57mm spacing so you would need to use taida Parts to put it together since most GY6 engine are 54mm spacing

www.drowsports.com/product/652/Engine/Crankshaft_Kit/Taida_GY6_150_Long_Crankcase_Set__57mm)

[Moat]

Aug 8, 2012 12:39:29 GMT -6 Alleyoop said:

Little contradiction there don't you think: the builder most likely left out a case locating pin. Maybe they did not come with alignment pins.

"Most"? Umm... not quite what I said.

The GY6 parts illustrations I've seen always show two locating dowel pins between case halves, FWIW. Just a thought, another possibility is all...

[Alleyoop]

Sorry "MORE"
Alleyoop