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Birdy426

Compression test with an autodecomp cam

8 posts in this topic

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?

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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?

Birdy

Maybe you could push or tow the bike a bit , as in when you jumpstart, with the compression gauge plugged in to the cylinder. That'll spin fast enough to retract the decomp pin for an accurate reading.

Was your 155-160 psi with the old cam and the 444 kit, or with the old cam and before the 444 kit?

As for your cooling problem, my 400 started boiling over a lot for no apparent reason a while back. It drove me crazy so I used an infrared camera to see if I could spot a problem. The right rad was bent down a bit from crashing, and was a bit closer to the header pipe than normal. The infrared showed that the pipe was actually heating the bottom of the rad, causing the coolant to boil over.

I tweaked the rad a bit and loosened the header pipe and adjusted to give max clearance. I only got an extra 3/8 of an inch, but it cured the problem.

In the 1st pic below, my range was set so red is hot and blue is cold, as per the scale on the side. Anything white is above the hottest range I had the camera set for. You can see that the pipe and the bottom of the rad are the hottest points in the pic.

The 2nd pic was taken after I adjusted the clearance. The range is slightly different, but you can see that the pipe isn't affecting the rad nearly as much.

Rradexheated.jpg

heatshield2.jpg

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Frostbite-

Thanks for the quick reply! The 155-160 was with the stock bore and a 13.5:1 wiseco piston. I think I'm just gonna go spend the coin on a leak down tester, as I have worked around not having one on several other "projects"...my time is getting to be worth more than that.

What kind of work do you do that you have access to an IR camera? That's pretty trick! Good find, too! I'm not too concerned with how much coolant is boiling off into the catch tank. It's always cooked off about the same amount, even when stock. What concerns me is that I'm not recovering the coolant as the bike cools down. I'm really at a loss here, as I have tested and replaced just about everything I can test or replace. I thought I had it knocked a couple of weeks ago, but with the price of gas I've been riding to work a couple of days a week, and it still persists.

Is the snow melted enough that you can enjoy the new scooter? I followed your thread on getting the bike home, and was really impressed with your ingenuity and creativity.

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Frostbite-

Thanks for the quick reply! The 155-160 was with the stock bore and a 13.5:1 wiseco piston. I think I'm just gonna go spend the coin on a leak down tester, as I have worked around not having one on several other "projects"...my time is getting to be worth more than that.

What kind of work do you do that you have access to an IR camera? That's pretty trick! Good find, too! I'm not too concerned with how much coolant is boiling off into the catch tank. It's always cooked off about the same amount, even when stock. What concerns me is that I'm not recovering the coolant as the bike cools down. I'm really at a loss here, as I have tested and replaced just about everything I can test or replace. I thought I had it knocked a couple of weeks ago, but with the price of gas I've been riding to work a couple of days a week, and it still persists.

Is the snow melted enough that you can enjoy the new scooter? I followed your thread on getting the bike home, and was really impressed with your ingenuity and creativity.

I inspect buildings and I use the camera to find heat loss problems or electrical problems – bad connections or overloaded circuits will heat up and are easy to spot with the camera.

You’re still having that problem, I thought it was solved? Is it possible that the hose from your rad to the overflow bottle is old and weak and collapsing under vacuum? That would let coolant under pressure flow easily to the bottle, but if vacuum collapses the hose it would be difficult for coolant to get drawn back to the rad. Is it the stock hose or have you replaced it with a different type?

You’ve probably already checked this, but if the drain from the overflow bottle is clogged it could cause the problem too. Have you tried popping off the drain hose completely to eliminate that as a problem?

If you pop the overflow hose from the rad and (for lack of a better term) suck on it, does air flow freely?

I have a spare rad with a new cap and I just tested it. I can’t create enough pressure in the rad to cause air to leak past the cap and out the overflow, but it takes almost no vacuum to cause air to leak past the cap into the rad. It takes so little vacuum to draw into the rad, that it should be easy to draw from the overflow bottle if the line is good and the overflow bottle drain hose isn’t plugged.

As for my riding, I’m in the worst season now. The temp is just above freezing so the snow isn’t melting away, but it’s too soft to ride on. My riding now is limited to driving on the roads in town, all 1.5 miles of them. Haha.

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Ya, I thought I had this fixed, too. It worked fine in the garage and on a short ride near home, but when I started riding to work, the problem came back (or perhaps it had never left...)

I went to the Yamaha dealer this afternoon and bought new, factory hoses for the overflow bottles instead of the 3/16 Tygon tubes that I used to replace the old ones, and bought a new OEM radiator cap (34 bucks, holy crap!) instead of the aftermarket one that I replaced the original with, and again it passed the garage test. Won't be able to ride tomorrow as it's mother's day, and won't be riding to work this week as we start spring training for football Monday (I coach at our local HS), so I probably won't know if it's really fixed till next weekend.

Thanks for the suggestions. I'll post up with my results once I ride it to be sure it's fixed.

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Well, still no joy here. Pumps coolant into the recovery bottle but doesn't draw it back into the rads. I teed a combination vacuum/pressure gage into the overflow line, and ran the bike for a while. After about a minute, the cap started to vent, and there was about 1 1/4 psig in the line. Pretty normal, I think. On cool down, however, there was no vacuum, ever. I was expecting at least 6-8 inches of water, as that's the differential between the coolant tank inlet and the radiator inlet...Any suggestions?

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Birdy-

I assume you replaced the radiator cap so we'll skip that. Replace the line that goes from the cap to the overflow tank if you haven't yet. (I had that solve a similar problem even when I couldn't find any leaks) With that done you have to think about how the cooling system functions.

As the coolant in the closed system expands from heat it is purged to the the overflow tank. When it cools enough it shrinks and get's sucked back into the 'closed' system. If the system has a leak anywhere it can suck air. I've seen hoses and seals that would not leak from internal pressure ie: water, but would suck air back in when it cooled. This can happen anywhere in the system. Start being suspect of any place that has to seal- hose fittings, o-rings, gaskets etc.

As for the compression- go get the leak down tester. It's the best way to get a real idea what's going on in the cylinder anyway.

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=94190

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