piston locks up

[airwave]

have rebuilt and broke in , my ? is when i ride wot for 1 min it locks up then will start in less than a minute . is ths caused from the ring gap being to small ? have done leak dn test no leaks and plug chop shows no indication of lean situation im thinking ring gap but need confirmation.

 

[blasterfreek30]

what do mean by locks up at wot?

 

[brandoz28]

is it fully warmed up when you take it out?

sounds like it may be lean, or its not getting warmed up enough before going out and riding it

 

[airwave]

i mean it locks up and wont turn over then in seconds of locking up it will trurn over and start and run just fine un less i run wot for a minute or more

 

[airwave]

could ring gap be to small ror the expansion of piston

 

[airwave]

not lean either

 

[brandoz28]

what's the piston to wall clearance? and white kind of piston?

ring gap could be too tight as you're thinking.

 

[brandoz28]

could be too little ring gap. could be too little piston to wall clearance.


definitely something heat related.

 

[airwave]

its a vitos forged 72.5 and the clearance i dont know its the same machine shop ive used for about a hundred jug bores i get the specs from the piston manufactor and he does the rest bike runs fine for hours even if i run to wot and back it down just if i keep it at wot for a minute it gets hot and locks like the piston does not enough clearance at that heat range

 

[blasterfreek30]

do the wheels lock up at wot....just seems that if the rings did catch do to the heat expansion...all the force locking up at wot would still make that piston grind up and down for a few seconds, scoring the cylinder walls, so how could it start a seconds later when its still hot, it cant cool down that fast

 

[airwave]

my thought exactly but yea it locks tires and dont grind. sit for 1 minute and it starts back up with no probs and all the power,

 

[scotj77]

this is a really strange situation. i guess you know that though. i would just pull the topend. take a look at everything. take one of the rings off and put it in the jug to check the ring gap clearance. strange. hope this helps

 

[airwave]

yup, tomorrows project. was just wonderin if someone knew or heard of this. head scratcher

 

[killer454]

i agree with the guy above me,if it is locking up at wide open throttle you have serious problems.for one the piston and wall are geting messedup.not to mention the stress on the rod wow.
you need to do a teardown and find the problem.


this is just my outlook on your problem

did you check the rod and rod bearing before rebuild?

 

[scotj77]

i agree with the guy above me,if it is locking up at wide open throttle you have serious problems.for one the piston and wall are geting messedup.not to mention the stress on the rod wow.
you need to do a teardown and find the problem.


this is just my outlook on your problem

did you check the rod and rod bearing before rebuild?

i have had two bottom end rod bearings go bad on me and both times it started to come apart and put all sorts of metal in the combustion chamber before it ever even acted like it wanted to lock up so i doubt that is what his problem is. and it is really noisy. no way you could miss it

 

[killer454]

yes i was just agreeing with what you told him scotj77 and just thought i would ask about the rod and bearing.

i agree with what you told him,he needs to take it apart
im sorry if i offended anybody on my statement

 

[CHutzell]

sounds like heat seizure

big bore kits are notorious for this problem,since your running an oversize piston it makes it even worse,the cylinder is not dissipating enough heat.My advice would be shut it off for awhile to let it cool(before it seizes up)chances are your piston and cylinder walls are scarred up pretty bad if its happened more then once

 

[scotj77]

yes i was just agreeing with what you told him scotj77 and just thought i would ask about the rod and bearing.

i agree with what you told him,he needs to take it apart
im sorry if i offended anybody on my statement

no offence at all man i was just adding to your comment with what i have learned my self. i wasn't tryin to crush your comment or anything.

I have seen plenty of guys on here with bb kits that run the hell out of them all the time and they never seize up.

Are you sure about the no air leak thing? what kind of leak down test did you perform? this sure sounds like an air leak.

 

[airwave]

CHutzell, if you know of a common problem , do you know what the salution is? i can tear the bike apart but if i dont know a fix its a waste of time to put back together for the same resualt . i have never heard of the problem but iam anxouis for fix.can ya make the heat disapate faster or should i hone and try for a little more clearance

 

[sicivicdude]

Let the quad warm up properly before riding...

Think about it, the flame front temperature of a gas engine can be 1800 deg F. Aluminum slug inside of a steel cylinder. Aluminum expands exponentially more than steel. As the piston heats up quickly it grows quickly. The steel doesn't expand as much OR as fast. If the piston gets hot FAST it can "lock up" and then as soon as the engine's heat equilibrates, it releases again. The problem is exacerbated on a big bore cylinder because of the diameter of the aluminum slug meaning more overall expansion with heating.