Top Dead Center

[speedfreek]

My friend just built his 250r top end and something is wrong with it. He says it only has 80psi. He said that the piston looks like it was down in the hole at least 3/16'' while at tdc. He is referring to the outer edges of the top of the piston, not the center of the dome. I told him that I think it should be all the way to the top. He said that he found out that wiseco sells .5mm different pin height pistons. Do yall think he has the wrong piston?

The bike is an 86. I checked the cylinder and it is an 86. He ordered a new hot rod crank that is supposed to be the short rod. There is no spacer plate under the cylinder. I saw the piston and it def was the 86 and earlier type. Stock head and gasket.

Any ideas?

[hartwill]

he Probly got the wrong piston. the pin location was changed in 87 to make up for the longer rod. you can tell what year it is by the intake cut out in the piston. I believe the 86 piston has a square window cutout for intake and later years have a half moon cut out. I may have these mixed up someone else can verify. hope this helps but please verify this info with someone before jumping to conclusions.

[Pumashine]

Originally posted by speedfreek
He said that he found out that wiseco sells .5mm different pin height pistons. Do yall think he has the wrong piston?
I saw the piston and it def was the 86 and earlier type. Any ideas?

So you are saying is a 86 piston with the pin height of the 87-89? Weird but maybee not. I would call Wiseco.

[speedfreek]

It was def a 86 piston with the "half moon" in the skirt. Yes it would be wierd if they had one with the pin .5mm higher.

[hondamancbr03]

Originally posted by speedfreek
It was def a 86 piston with the "half moon" in the skirt. Yes it would be wierd if they had one with the pin .5mm higher.

If the piston has a half moon cut out in the skirt then he has a 87-89 style piston.

Plus when you mentioned that the piston sits down about 3/16", just by eye that's about the distance the 5mm makes.

[Pumashine]

Originally posted by hartwill
I believe the 86 piston has a square window cutout for intake and later years have a half moon cut out. I may have these mixed up someone else can verify.

If the piston has a half moon cut out in the skirt then he has a 87-89 style piston.




Yes I believe you both the two mixed up. 86 has the half moon and 87-89 has the rectangular window. Maybee if we all vote we can come up with the correct solution! LOL

[hondamancbr03]

Originally posted by Pumashine
Yes I believe you both the two mixed up. 86 has the half moon and 87-89 has the rectangular window. Maybee if we all vote we can come up with the correct solution! LOL

No voting necessary:)....I just walked to my bench and opened the box of a brand new later style piston and gazed upon a square window....You are correct, 87-89 square window. Should have gotten out of this chair and checked in the first place:ermm:

[hondamancbr03]

Originally posted by hondamancbr03
No voting necessary:)....I just walked to my bench and opened the box of a brand new later style piston and gazed upon a square window....You are correct, 87-89 square window. Should have gotten out of this chair and checked in the first place:ermm:

A picture says a thousand words.....If you see this through the intake, you have a 87-89

[Pumashine]

Originally posted by hondamancbr03
No voting necessary:)....I just walked to my bench and opened the box of a brand new later style piston and gazed upon a square window....You are correct, 87-89 square window. Should have gotten out of this chair and checked in the first place:ermm:

LOL! Yeah I did the same thing. The motors and parts are in the room 3 doors down.

Unless he's got the wrong rod on their it seems kinda stange the 86 piston could sit down 3/16" at TDC without having a spacer plate..

[hartwill]

it cant be the wrong rod, a long rod crank and an 86 piston would be too long for the cylinder. thats wierd. did he maybe forget to put the needle bearing in? dont mean to insult him but thats the only other thing i can think of. lol we have all done dumb things before. maybe post a pic. or did he maybe order a 250x piston?

[speedfreek]

Originally posted by hartwill
it cant be the wrong rod, a long rod crank and an 86 piston would be too long for the cylinder. thats wierd. did he maybe forget to put the needle bearing in? dont mean to insult him but thats the only other thing i can think of. lol we have all done dumb things before. maybe post a pic. or did he maybe order a 250x piston? I will ask him about the bearing. This could be it (i hope he's not that stupid), lol.

Does the 250x piston have the half moon in one skirt?

[hartwill]

please keep us informed on what's wrong kinda interesting.

[speedfreek]

I talked to him last night. When I asked him if he put in the rod bearing he thought for a second, then hung his head and said no. I immediately kicked him square in his butt! lol. I hope it didn't beat the rod end out of round. He only idled it and said there was a noise in the top end so he shut it off. I am ragging him hard. I will remind him of this stupid thing for many years. lol.

hartwill, you were correct. Thanks again

[Pumashine]

Originally posted by speedfreek
When I asked him if he put in the rod bearing he thought for a second, then hung his head and said no.

Thats some funny chiat right there. I can't say I have never done anything wrong. I hate it when your all done torqueing the cylinder and head and look over to see the circlip for the piston.

[hartwill]

lol. I couldn't think of anything else it could be. glad you guys figured it out though. its always somethin stupid.

[2-330s]

Originally posted by Pumashine
Thats some funny chiat right there. I can't say I have never done anything wrong. I hate it when your all done torqueing the cylinder and head and look over to see the circlip for the piston.
lol ever seen a piston put in backwards? bought a 250r that was just rebuilt,didn't run well. he was told by the enging builder it was the ignition.