compression(or lack of)

[mod440ex]

My question; I had to replace my valve cover gasket so i washed my quad at the car wash. I let it set in the back of my truck all night, and it got pretty cold. I took it to work with me to show a friend the new shocks and exhaust i put on, tried to fire it up, still cold outside. it cranked for a little bit then backfired. After it backfired it started cranking over funny, and almost acted like it didnt have any compression. When i got home i tried to see if i could see anything wrong. pulled the valve cover off and eveyting looked ok, cam chain was tight and valves where still adjusted coerrect. pulled the plug off and there was some ice inside the chamber. called my dad and he said i might have a piece of ice holding a valve open so i put it next to a heater for 45min. put it back together and still sounds funny. it feels like i have compression ,but when i crank it over the starter and one way bearing sounds different, so pulled the flywheel cver off and evything seems to be tight. I am lost, anybody with some info would sure help me out alot.

[m36indiana]

ck the keyway under the flywhell, mine broke the other day , it wouldnt run and backfired

[mod440ex]

did u get the key from honda or just go to a auto store

[mod440ex]

did u get the key from honda or just go to a auto store, is the bolt standard thread or reversed thread. thanks

[m36indiana]

i got a woodruff key from ace hardware, had to shave it down a bit to fit but works good, the bolt is regular thread.

[NRTHBUSH]

sounds like u cold seased your engine to me. we had a 500 bike (cr 250 frame with a 500 engine)do that to us today. the kick start moved to easly after that. cold seaseing it cuased the bike to loose compresstion and it wouldnt start. had to tear the bike down and put in a differnt engine in the cold.

[mod440ex]

well after it backfired i pulled the plug and stuck a screwdriver in the head to make sure the piston was free. I dont really want to put a new engine in it any other suggestions if thats what happened to it.

[mod440ex]

what exactly is cold seasing, and what is it caused from. It has always been hard to start when its cold because of the high compression piston, just hooked up a battery booster and it would start.

[GPracer2500]

Originally posted by mod440ex
what exactly is cold seasing, and what is it caused from. It has always been hard to start when its cold because of the high compression piston, just hooked up a battery booster and it would start.

Pistons and cylinders expand as they come up to operating temperature. But they generally won't expand at the same rate. A cold seize is when an engine is not warmed up properly and the piston expands too fast compared to the cylinder. If you start an engine and immediately peg the throttle the piston can expand so quickly (relative to the cylinder) that it will stick itself in the bore. Poor engine warm up habits will cause unnecessary wear on the piston and bore even if you never actually have a piston seize from this.

I cringe when I hear folks start up there engine on a cold morning and immediately start giving it hell.


Water/ice inside the combustion chamber is bad news. I'd start with a compression check and go from there.

[mod440ex]

it never started when it did this, it just backfired. could that still be a the problem or does it have to run to seize.

[NRTHBUSH]

if it back fired u probaly flooded your engine. is your kill swich in the off position? if it is the bike will crank over but not start. maybe u bumped it. check ur gas is it turned on. are u geting spark? if u have lack of compresstion its time to get your heads ported and polished and new cilenders. also would be a good time to put a big bore kit in to.

[GPracer2500]

Originally posted by mod440ex
it never started when it did this, it just backfired. could that still be a the problem or does it have to run to seize.

The engine has to run to cold seize. Although any engine can cold seize, it's a phenomenon not often associated with the 400EX.

[mod440ex]

if it backfired it got spark, the plug was deffinately fouled changed it and it feels like it has compression it just wont start. i ordered a flywheel puller so i can check my flywheel key. hope thats what it is

[mod440ex]

checked my flywheel key and its not sheared, i am at a total loss for what is wrong with this thing. i will pull the head off today and see if i see anything wron. keep givin me input i can sure use it.

[GPracer2500]

I'd do a compression test before you remove the head. It only takes 2 minutes. If you don't have a tester, you can probably get a loaner from Autozone or somewhere with a tool-loan program.

[mod440ex]

i will have to pull the valve cover off wont i, i have a hard enough time changing spark plugs in that little space. Do you know right off hand or know where i can find out what a 440 12.5:1 pistons compression should be

[GPracer2500]

Originally posted by mod440ex
i will have to pull the valve cover off wont i, i have a hard enough time changing spark plugs in that little space. Do you know right off hand or know where i can find out what a 440 12.5:1 pistons compression should be

No. I've done it without removing anything. You'll need a comp tester with a 12mm adapter (smaller than most automotive types). Walmart sells an inexpensive comp tester that includes a 12mm adapter.

There's no published spec for what your compression should be. The cam specs and the gaskets you've used will impact what the cranking compression will be. I could make an educated guess--but this is why a comp check should be done on every rebuild as soon as the rings are broken in. It gives you a reference for future comparisons.

But that's ok. I'd just be looking for a number that is obviously lower than it should be. If a compression loss is keeping it from running then a comp check will reveil that.

[mod440ex]

do u know about how far the key on the crank should be sticking out of the crank. Mine is almost flush with crank, it s on the flywheel side. went and got a comp test from walmart and i am trying to get the flywheel back on correct.

[GPracer2500]

Originally posted by mod440ex
do u know about how far the key on the crank should be sticking out of the crank. Mine is almost flush with crank, it s on the flywheel side....

I'm not sure I get what your saying.

[mod440ex]

well i went and got a new key put it on< dont think thats what was wrong. I hooked the compression tested up and cranked it over and it still sounded like it did before, and all of a sudden it went back to normal. I put the plug back in and it fired right up. what the f***????? Oh well its running