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Tillerman6

74 TY 250A PISTON & RING ISSUES

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Guys, 

    So after getting my parts back from Millenium Technologies- new bore on Ebay cylinder and new piston- I noticed quite a bit of vibration.  So today I tore it down again and weighed the new piston, pin, upper end bearing and compared those weights to the ones on the original parts.  As I expected, the new piston was significantly heavier than the old original piston, even though the piston size was still the same.

 

Old Piston 213 gm  New piston 241gm  a delta of 28 grams. 

Old pin 57 gm         New pin 60 gm    delta of 3 grams

The remainder of the parts were too light to measure on the scales I borrowed, so I am forced to ignore those results.

So with this much difference in weight it is no wonder that the bike is trying to shake itself to pieces!

But there is no way to shave enough material off that new piston to make it match the weight of the old one!

So the hard choices seem to come down to :

A- try to find new rings?  434-11610-00 (standard size)

B - I may have found a set of 1st oversize rings - but can these be shaved down enough to work in a standard size bore?

C  polish up the old rings and use them again?  The scratches are only about .005" deep (I am guessing) and the piston has some scuffing, but is not too bad

.Fresh bore on a different cylinder.  The new piston ran in the fresh bored cylinder without a problem except for the vibration.

D If you have any ideas?

I am very tempted to put the old piston back in as is if I can't find any new rings for it anywhere else?

 

 

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 So have you changed the main bearings? Pistons do not make any vibration. Rods and mains cause vibration.

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20 hours ago, lineaway said:

 So have you changed the main bearings? Pistons do not make any vibration. Rods and mains cause vibration.

No I have not changed the main bearings. there is no detectable looseness in any of the bearings that I can feel.  Triple checked the rod and the upper and lower needle bearings. crank halves do not appear to wobble when the cylinder is off. Bike idles fine, pulls good (no wheelies)  But while we're on that subject, - can you change the main bearings without splitting the cases?

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19 hours ago, copemech said:

Look up B&J racing and give them a call.

For what reason?

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9 hours ago, Bmonk said:

Looks like a YZ piston...what are the numbers on the piston crown?

0899F AND UNDER THAT 234M07000 .  Says it fits YZ250 76-79 and IT250 78-80

9 hours ago, Bmonk said:

Looks like a YZ piston...what are the numbers on the piston crown?

 

9 hours ago, Bmonk said:

Looks like a YZ piston...what are the numbers on the piston crown?

 

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3 minutes ago, Tillerman6 said:

No I have not changed the main bearings. there is no detectable looseness in any of the bearings that I can feel.  Triple checked the rod and the upper and lower needle bearings. crank halves do not appear to wobble when the cylinder is off. Bike idles fine, pulls good (no wheelies)  But while we're on that subject, - can you change the main bearings without splitting the cases?

No, the center cases have to be opened. Top ends do not vibrate. Since you had a loose needle bearing, I would do rod and mains. The bike is 44 years old. The only reason I would take the time to do it is it could go another 40.

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37 minutes ago, lineaway said:

No, the center cases have to be opened. Top ends do not vibrate. Since you had a loose needle bearing, I would do rod and mains. The bike is 44 years old. The only reason I would take the time to do it is it could go another 40.

Lineaway, maybe you have an old stock Ty250 piston?  If I knew how much yours weighs, then that will help eliminate that the piston might still be the wrong one!  It should weigh 213 grams and the pin should weigh 57 grams if it is like mine????

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Just now, Tillerman6 said:

Lineaway, maybe you have an old stock Ty250 piston?  If I knew how much yours weighs, then that will help eliminate that the piston might still be the wrong one!  It should weigh 213 grams and the pin should weigh 57 grams if it is like mine????

I know that the front forks stopped vibrating so hard that the bike was backing up on the side stand while it was parked in the driveway idleing after I went back to the much lighter old piston.

Maybe the right l one is even less weight?

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 The weight really does not matter. What actually started the engine rebuild in the first place?

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1 minute ago, lineaway said:

 The weight really does not matter. What actually started the engine rebuild in the first place?

It was making a hell of a racket  like metal on metal pinging. but it does not do that now.

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14 minutes ago, Tillerman6 said:

I know that the front forks stopped vibrating so hard that the bike was backing up on the side stand while it was parked in the driveway idleing after I went back to the much lighter old piston.

Maybe the right l one is even less weight?

That analogy is flat out silly, I have seen brand new out of the crate bikes vibrate on the side stand!!!!!

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Well with the heavier piston it it the side stand would slip and the bike would roll backwards. Also, while riding it , my hands would go numb in about 30 minutes just put-putting around. No high revs

allowed.My chain saw was much smoother than this thing was.  Now it's about 50% less vibration- at least it's back to where it was after i put my old and much lighter piston back in.!

Somebody on here must have a bonafide 438-11631-00-96 or 98 laying around that they could weigh and take pictures of?  Thanks for trying anyway Lineaway. 

 

Edited by Tillerman6
New info

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