Compression a little low when hot

[thumper_calgary]

Getting my bike ready for a trip down to Baja over xmas. It's an 03 that doesn't have a ton of hours on it and was well maintained by the previous owner. starts and runs fine, lots of power, no smoke and it doesn't use any oil.

 

I noticed last summer that when it was hot the compression felt a little lower when kicking it over. The bike never feel like it has a ton of compression, which I know is all relative and yes I know it has an auto decompression mechanism.

 

Here's my question: should I be worried at all? I'm going to try and lay my hands on a leak down tester when I get home. I've only got a week off work before xmas to get the bike ready so time is of the essence. I'm going to check my valve clearances as part of my pre-trip tear down. I could MAYBE get the rebuild done before I left but it can take a long time to get parts up here in Canada and I doubt I would be able to get the bore mic'ed and a new piston installed within a week. Especially if I needed head work done.

 

Am I being parinoid?

 

 

[FORMA MOTO]

Probably.

If it starts well cold and hot, idles well with a properly adjusted fuel screw, and doesn't gulp oil, it's probably just fine.

[bobpara]

My '06 WR 450 has a manual decompression lever.....you say yours is automatic.

I had an automatic decompression cam on a 1500cc Kawasaki Vulcan, same thing. I ran a compression test and got low numbers. I was bummed! The bike had only like 6,000 miles on it....how could this be !?

After numerous conversations with dealers I came to the conclusion just leave it alone until it smokes or something bad happens. I'm not so sure if its even physically possible to do a proper compression test on a bike with a decompression cam (automatic)

I am highly against owning another bike with an auto decompression. The mechanical complexity, things that can go wrong, cant do a comp test....everything. Never again.

I would check the valve clearance though.

[FORMA MOTO]

My '06 WR 450 has a manual decompression lever.....you say yours is automatic.

I had an automatic decompression cam on a 1500cc Kawasaki Vulcan, same thing. I ran a compression test and got low numbers. I was bummed! The bike had only like 6,000 miles on it....how could this be !?

After numerous conversations with dealers I came to the conclusion just leave it alone until it smokes or something bad happens. I'm not so sure if its even physically possible to do a proper compression test on a bike with a decompression cam (automatic)

I am highly against owning another bike with an auto decompression. The mechanical complexity, things that can go wrong, cant do a comp test....everything. Never again.

I would check the valve clearance though.

Your '06 does have auto decompression. All WR's from 2003 have one.

Virtually all fourstokes on the showroom floor have them now.

If you have a lever on the bars, that is the hot start.

 

Auto decompression is three moving parts and a spring, it's not complicated and the rarely fail.

You are focusing on the wrong thing.

 

Your cam chain and cam chain tensioner will fail way before anything else, and they can cause catastrophic failure........

You can rarely ignore a motor until you feel like repairing it. It needs it when it needs it.

By the time it is burning oil, it's too late, unless you are lucky and nothing breaks or the cams do not jump timing.

 

Pull you motor apart when you have time and do a service limits test with a micrometer on everything above the rod. That is the only valid test.

Then use an hour meter to gauge your next service times.

[miweber929]

My '06 WR 450 has a manual decompression lever.....you say yours is automatic.

I had an automatic decompression cam on a 1500cc Kawasaki Vulcan, same thing. I ran a compression test and got low numbers. I was bummed! The bike had only like 6,000 miles on it....how could this be !?

After numerous conversations with dealers I came to the conclusion just leave it alone until it smokes or something bad happens. I'm not so sure if its even physically possible to do a proper compression test on a bike with a decompression cam (automatic)

I am highly against owning another bike with an auto decompression. The mechanical complexity, things that can go wrong, cant do a comp test....everything. Never again.

I would check the valve clearance though.

You more than likely will never own another motorcycle made after 2002 again, then, as EVERYTHING "modern" has an auto compression release system of some sort or your electric starters would be 5x the size they currently are. And same with kick only bikes, everything has some system on it to ease starting.

 

It's one of those things people who are used to working on older bikes hate: not being able to run a compression test like they used to do; trust me I get it, been working on stuff for 30 years. But a leakdown test will work fine with an auto decompressor and actually give you a far better check of the motors health than a compression gauge does.

 

Don't fight it, just go with it; same with FI, just enjoy the benifits.

 

Mike

[bobpara]

Thumper_Calgary: Be careful of the 'advice' you get on this site. I know I will be from now on. You have nothing to worry about I think.

Krannie: I don't know what is wrong with you?, you seem to take enjoyment in scaring the crap out of people and overcomplicating the crap out of something. Are you suggesting he pull his motor apart !! ??

miweber929: I guess you and I are two very different people. I like simplicity and serviceability in a design.....do you see a decomp cam in a Harley or a Ducati? Nope, they put a beefy starter motor in and geared it properly, they did not try to save 2 oz weight by using an anemic starter and looked to save weight in other places. You also speak of FI as some magical cure. There are numerous people out there with problems with FI and when it happens, you can't re-jet, you are SOL.....

[FORMA MOTO]

Krannie: I don't know what is wrong with you?, you seem to take enjoyment in scaring the crap out of people and overcomplicating the crap out of something. Are you suggesting he pull his motor apart !! ??

miweber929: I guess you and I are two very different people. I like simplicity and serviceability in a design.....do you see a decomp cam in a Harley or a Ducati? Nope, they put a beefy starter motor in and geared it properly, they did not try to save 2 oz weight by using an anemic starter and looked to save weight in other places. You also speak of FI as some magical cure. There are numerous people out there with problems with FI and when it happens, you can't re-jet, you are SOL.....

 

I know the truth is scary, but it's the only path to happiness.

I am suggesting that if he is concerned, he has no other option. 

Low compression means there is a problem. 

You can't guess it away.

 

A 2003 motor MUST need some service, even if it sat the whole time....

It's better to find it , fix it, and move on, than wait for something to break, in my opinion.

It takes about 4 hours to replace the piston and rings, so it's not 'overly complicated crap', now is it.

 

You seem to take enjoyment in making something you like as something we all should like too. Not so.

 

 

 

 

Oh, and the most performed motor upgrade to a harley is adding the auto-deompression valve system....

You must be thinking 1975 or something....

 

...and Ducati has had auto deompression now for a while...

 

An interesting trick Ducati has employed on the 1199 is the use of what they call an “auto-decompressor” to make the engine turn over with less effort from the starter. A flyweight at the end of each exhaust cam gear retracts at super-low speed to rotate a protrusion from the concentric side of the cam, thus creating just enough valve lift to relieve the pressure on the piston for easy startup. If you’ve ever had the pleasure of starting a Ducati, you’ve felt that anxiety just as you press the starter button as the engine struggles to turn over. The auto-decompressor alleviates that worry, and as a side benefit also allows the use of a much smaller (read: lighter) starter and battery.

 

Besides, one is an overweight dinosaur of non-performance, and the other is a fragile toy that requires the removal of 25 bolts to service anything. 

 

 

Oh, and remember, your 2006 WR450 has auto-decompression and does not come with a manual compression release, so it's time for a reality check there buddy...

Now, if you went and installed a manual compression release on a motor that already has automatic, then that explains a lot of your attitude issues!  

Edited November 26, 2013 by Krannie

[grayracer513]

EVERY WR450 ever made has always had auto decompression, Bob, even yours. The lever is a hit start valve, intended to lean the engine out for high temp restarts.

[thumper_calgary]

Thanks for the thought's all.

 

The cam chain issue is a good thought. I know there was much debate about manual vs automatic cam chain tensioners on my old DRZ

 

Any way to check the wear on the chain? or do anything but inspect the tensioner ? I'm sure there is a guide block in there to inspect..... anything else to look at?

[beezer]

The 03's had a problem with shearing flywheel keys.

 

Then you get to walk back to the truck.

 

Don't ask me how I know this.

 

I'm sure you'll be fine as God seems to protect people like you.

 

Just go down there and ride and don't give the bike a second thought.

 

Don't forget to take lots of pictures and give the class a full report when you get back.