Compression Test with AutoDecomp Cam

[Birdy426]

I have a Hot Cams autodecomp exhaust cam in my 01 WR, along with a Luke's Racing Big Bore Kit. While I haven't noticed any change in performance since I put it together a couple of thousand miles ago, I ran a compression check today while trying to troubleshoot a cooling problem.

The best reading I could get, after kicking the bike thru a half dozen times was about 95 psi. Is this normal for a bike with an autodecompressor cam, as I doubt I am spinning it over fast enough to retract the pin? I didn't do a compression check after I broke the motor in, so I don't really have a reference fro what it "should" be, but with the old 01 cam, it wold pump out about 155-160 psi. If that's normal, then is the only way to check sealing to do a leak down test?

While I'm posting up, maybe someone has some ideas on my cooling problem, too...

It's a WR, so it has a catch tank. During an average ride, I boil off 6-8 oz of coolant into the catch tank. As the bike cools, it should draw the coolant back into the rads from the catch tank. It's not. After everything is cooled down, the coolant is still in the catch tank, and the level in the radiators is below the fins. I have replaced the radiator cap, replaced the hoses to the catch tank and overboard vent, checked them for kinks, and even completely flushed the system to be sure there aren't any "boogers" in there blocking the passages. Any suggestions?

[grayracer513]

The only conclusive test for cylinder sealing is the leak down. 95-110 is the right range with AD, but it still depends on too many factors to be very accurate.

Your recovery system is failing to recover because there is an air leak somewhere between the cap and the hose at the bottom of the tank. When the coolant cools, it contracts, and that creates a vacuum which is supposed to draw back coolant from the tank. If air leaks in instead, it doesn't. The leak normally happens between the cap and the top of the radiator neck. There should be a gasket there if the cap was made for coolant recovery. Standard caps typically don't have one.

[Birdy426]

Your recovery system is failing to recover because there is an air leak somewhere between the cap and the hose at the bottom of the tank. When the coolant cools, it contracts, and that creates a vacuum which is supposed to draw back coolant from the tank. If air leaks in instead, it doesn't. The leak normally happens between the cap and the top of the radiator neck. There should be a gasket there if the cap was made for coolant recovery. Standard caps typically don't have one.

Gray-Thanks for the quick reply. That's the road I've been going down with the coolant recovery system...The new cap that I put on does have a gasket, but knowing that "new" doesn't always mean "good" I tried the cap from my son's WR250 (which recovers coolant just fine). Still no joy. About the only thing I haven't done (besides find out what the real problem is) is pressure check the radiators to see if they are venting off vacuum...however, I don't think there would be a "check valve" in any kind of leak so if they were venting vacuum, they would vent coolant as they heat up. I'm really at a loss here, as I have tried just about everthing I can think of...looking for the unobvious, second order effects I guess...

Birdy

[grayracer513]

Next, remove the overflow line at the radiator and apply a vacuum to it. It should hold that vacuum. After that, then you'd be correct that the cooling system needs a pressure test.

[Birdy426]

Hooked the MityVac up to the radiator overflow outlet and pulled a vac. Held strong with the cap on. Sucked on the overflow line while it was disconnected and got a mouth full of Coolanol.

Went to the Yamaha dealer, gave them 34 bucks for a new, OEM WR Radiator cap and 12 bucks a piece for new lines for the rad to catch tank and catch tank overboard. The other replacement stuff was just 'generic' stuff. We'll see what happens.