Jump to content
Sign in to follow this  

No compression on '10 CRF450R after rebuild

Recommended Posts

Just replaced the cylinder, piston and rings (OEM) and upgraded the valves and springs with kibblewhite.  Adjusted the valves, timing is set and have no compression.  Pull started the bike and it fired up and will run with the "choke" pulled.  Bike won't run under regular idle and still has no compression.  Checked everything too many times to count and am completely lost.  Any ideas would be greatly appreciated.  Thanks in advance.

Share this post


Link to post
Share on other sites

Did you stagger the ring end gaps properly? There are only 3 places to lose compression. The rings, the valves and the head gasket. Is there a chance you messed up the automatic decompression mechanism?

  • Like 1

Share this post


Link to post
Share on other sites

Gaps are good, had my tech put the cam back in but looking thru the service manual I can check the decomp to ensure it's correct.  Would that cause the bike to shut off after it's warmed up if it's incorrect? 

Share this post


Link to post
Share on other sites

Who did the head work? If you are sure the timing is good, then pull the head off, flip it over and get it level. Cover the so valves with carb or brake clean. Take a blow gun and blow into the intake and ex.ports and look for air bubbling in the fluid. Bubbles means valve not making a seal.

Share this post


Link to post
Share on other sites

I think your timing is off. That would make kick starting hard and wont run properly

No the kicker wouldn't be hard. If the timing is one tooth advanced it will be very easy. If its retarded a tooth it will be a touch harder to roll over.

What Cleared may mean is if the deco is adjusted wrong

Share this post


Link to post
Share on other sites

Just another thought. Did you actually check the compression or just assume it is bad? Could be loose ground on the coil which has to be undone to get the head off. Just start diagnosing from scratch and don't assume you have an engine problem. Make sure the gas is on-HA!

Share this post


Link to post
Share on other sites

So after ANOTHER call to kibble white today, come to find out the first guy I talked to on Friday is kinda clueless.  My machinist is also slightly to blame seeing as how the intake springs were on the exhaust valves and the exhaust springs on the intake valves.  The first kibble white rep said the buckets are SUPPOSED to be tight since its a double spring system instead of a single spring.  I wanted to get a second opinion so after speaking with a different rep he informed me that the springs were indeed on the wrong valves.  Swapping those around tomorrow and that will more than likely fix my problem.  At least I get to learn all this on my first engine rebuild. 

  • Like 1

Share this post


Link to post
Share on other sites

Wow I hear there are a lot of uninformed want to be mechanics out there.

Next thing your machinist didn't do is set the "valve spring pressure installed hight". The spring in the closed valve position must be at a value set by the valve train company. Then the valve spring has to be checked at full valve opening. This is determined by the can lift. The spring seat pressure in the open position is really important to prevent premature valve wear an valve floating. Then the spring needs to be checked for coil bind.

Did he put on new valve stem seals?

There are shops that do things right the first time and others that don't.

Share this post


Link to post
Share on other sites

Sounds like you may have tagged a valve and it is not sitting on the seat straight any more. The valve should have closed tight enough with the wrong valve spring in it to have enough compression to fire off. And a valve spring should never be tight in a bucket. Springs grow a bit when you squish them. 

Share this post


Link to post
Share on other sites

Jesus. Thats why its just easier to go OEM valves.

Share this post


Link to post
Share on other sites

You can still bend OEM with the piston. There are no differences. The piston doesn't care. Stainless is the way to go. Stock one may not have bent it may have broke. Benefit of some stainless is it bends. Cam timing off in the beginning or a faulty cam chain tensioner can cause the valves to slap hands with the piston =ing No good. Do a vacuum test on the head. If you need any help please PM me or email me @ Jeff@aperaceparts.com. 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×