compression

[jays-z400]

Hello, i'm new to this forum.
I have a 2003 ltz400 that I got for $1800. Well the only way it would start is by popping the clutch.
So I checked the compression on it and it just had 30 psi. So I'm rebuilding the top end. I got new ring for the piston and all.
My buddy is making sure the jug is good and is going to hone it for me.
I am wondering if there is away to do a 12.25:1 compression with the gaskets or do you have to have an after market piston to go with it.
Sorry if this is posted in the wrong place.

[zookie400]

dont hone the jug, you will ruin it. it is a coated jug, not a old school steel sleeve.

the top end is probably fine, you should check your valve clearances first before tearing it apart. often the valves get tight and bleed compression off. a simple re-shim can solve your problem. check valve clearances and report back.

[beaverclever02]

+1 check valves before going any further

[CFM-Z440]

+2 this is usually just an intake valve problem from poor air filter maintenance.

[jays-z400]

I did check the valve clearances before I tuke it apart. My exhaust was great, but my intake was 0. so I have new valves and shims coming to. It has kibble and whites in it and that is what im puting back in it.
Okay so your saying not to hone it. If I don't hone it how will I get the new rings to seal.

[beaverclever02]

are you changing the rings cause you think thats the loss of your compression?

[jays-z400]

Beaverclever02:
At the time yes that was the reasoning. But from what you guys are saying now I don't think that. But since I already have the rings and have it apart I might as well go ahead and change the rings.

[biggiej42]

Are you sure it had kibble whites in it?? If so, check your air filter setup. Dust and dirt may have gotten in and chewed up the valves. If you don't already have a clamp on filter, modify your box to accept one. With a clamp on and regular cleaning/oiling you won't have to worry about wiping a set of kibble whites.

As far as compression, I believe changing the base gasket to the single layer drz-e gasket puts your compression at 12.2:1.

[jays-z400]

Biggiej42:
thanks man i will do that... but im still wondering about the new rings how do i get them to seal if i don't hone it...

[CFM-Z440]

Honing is necessary on plated cylinders. You need to use a high grit ball hone. What you don't want to do is use a rigid hone.

But like mentioned, your loss of compression is most likely only because of the intake valve cupping.

[jays-z400]

okay.. well im replacing the valves to.. what size grit would u say...

[zookie400]

CFM is correct about the honing, the reason is that you are not trying to remove metal but rather de-glaze the cylinder to re-expose the hatch marks that should still be present.

i picked up a trick from one of the pro teams engine guy at the track when i started racing, a fine 3m pad will deglaze and not harm the coating. plenty of people dont like this idea but i have had great results and have seen no longevity or compression differences when doing it the "right" way.

if your intakes were zero clearance, you should look at the intake/air filter like others mentioned, and dont worry too much about the jug and rings.

[jays-z400]

zookie400:
i understand not to worry about the jug but the problem is that i have already taken the jug off, so now i have to do something with it to put it back togeather... i can't just slap the jug back on there and hope for the best...

[zookie400]

honestly i bet you could just slap it together and it would run great. have you checked the ring gap yet? if they are not scored and the gap is within spec, put it back together and run it if you want.

[jays-z400]

well i already have the new rings, i still need the gasket kit tho cause the bottom gasket kind of riped alittle bit so.. but ur say i can just put it back to geather with out honeing it... what if i get some fine sand paper and whipe the jug clean and just scuff it up alittle bit..