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Frostbite

Strange compression loss and engine lock up

11 posts in this topic

I think there's a compression virus floating around this thread. XYZRacer lost compression a few days ago for no apparent reason and today a very weird thing happened to me. It was the first ride/break in run with the new hotcams and 430 kit. It was around -30 and I cruised around for about an hour with no problem. I figured I'd open it up a bit so I headed out onto the bay and was cruising along in top gear about 60 mph. After about 5 minutes she grogged out like a 2 stroke melting a piston and I rolled to a stop. I hoped that the carb had just iced up and tested the kickstart slowly. There was almost zero compression and then the kick lever stopped solid. I figured for sure I had bent a valve. 2 of my intakes were a tad tight and the new shims hadn't landed yet and I was crackin' to get out riding. I figured she got hot and a valve kissed the piston.

I put the bike in gear and rolled it backward a bit and then tried the kick lever slowly again. It turned a bit and then brought up solid. The only thing I could think of that would lock up the engine at a certain point and cause a loss of compression was a bent valve.

I sat on the bike for a few minutes thinking about the long cold walk back to town and then I rolled the bike backwards and kicked again and it kicked through, but still no compression. I kicked slow a few more times and it turned freely which was strange since I didn't put enough pressure on the lever to push the valve away from the piston.

Then I think that I cracked another throttle plate and a bit of metal was stuck under a valve holding it open and fell out when I turned the engine backwards, but the valve wasn't sealing. I waited for a while hoping a sled would come along and now and then would give it a few kicks. Gradually the compression started coming back. I'd get a little pop but with the low compression I couldn't kick fast enough to get it to run. After an hour a few friends happened by on sleds and I got one to tow me to try a bumpstart. He dragged me for half a mile before it finally caught and was running crappy but I kept it running and aimed for home. In a few minutes the engine cleared right up and was back to normal. I took it to the shop, checked a few things, found nothing, and went back out and rode for 3 hours solid running perfectly, all the while trying to figure out what the heck happened.

Then I wonder if it is possible that an intake valve iced up and froze open. :cry:

I've run the bike longer and harder in colder weather and never had this problem. Then I think that maybe the higher lift of the new cams is pushing the valves deeper into the guides and crap buildup is causing them to stick, but why only at high speed and not high revs in lower gears? The bike is running great so I head back out onto the bay for a test and sure enough after a few minutes she starts to crap out again. I pull in the clutch and keep it running and after a minute sitting still it clears right up and works perfectly again. It was getting dark and I was half froze so I headed to a superbowl party to thaw out.

I'm gonna do some more testing but this one's got me stumped. Anybody have any ideas? Any spaceships in the area lately?

Aside from the compression virus I had a great ride. My bike has been apart for months and it felt good to hit the slopes (although it's gonna take a while to toughen up to that brick of a seat again). One nice thing about riding in the snow is you never have to wash the bike. Here's what it looks like after 4 hours solid riding. My helmet vents iced up a lot and I had to stop every half hour and chip the ice out with a key so I could breathe, and I got a touch of frostbite on my cheeks, but that's just part of the deal up here.

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I did think of 2 other differences last night.

I had been running without the plastic rad fins for a few years. Before I got the ski I was crashing every day and my rads were so bent up the fins didn’t fit anymore. I got new rads and new fins last spring and I fixed an overheating problem. This is the first winter ride with the improved cooling system. Maybe at high speed the engine is getting overcooled allowing the intake valves to ice up. I couldn’t imagine that ice could form on a valve in a running engine but maybe if the coolant is getting too cold the frosty air could do it.

The other difference is the engine oil. I always run synthetic 0W40 but Hotcams recommends against synthetic for break in so I used the lightest oil in town, 5W20. Maybe it's thickening up with the overcooling and sticking the valves. I'll see if it improves when I switch back. I do know that the bike is a lot harder to kick over in the cold with the non synthetic.

I think I’ll invest in a temp guage and maybe a thermostat. Anybody out there have either?

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Frostbite, I wished I were a mechanic so I could talk more technically but I'm not... Something tells me that it's got to do with how cold it is outside :cry:

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Try blocking one or half of one of the radiators. It should help it stay hot and let you know if it's icing up from the cold.:cry:

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maybe the teflons are to blame, too stiff in cold weather, more friction

but the springs forcing the valves back are mighty strong

some resonance maybe at high speeds+cold?

options are many

my lady has no problems in cold, radiators squeezed to 85%, no boiling if idling long

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Thanks boys, looks like I've got some experimenting to do. I'm sure it's got to do with the cold too, but I've been riding here since 99 and this has never happened before. I think I may run it until it quits and then pop the carb and shove my helmet cam in the intake to get a look at what's going on in there.

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Frostibe, when you did this high lift cam and big bore install (nice write up on it by the way :cry: ) did you remove the valves? You mentioned the higher lift and guides. This is a real possibility. One need to remove the varnish on the stems. As the lift pushed the valves deeper, they can get hung up. We actually has the first generation Camry witht he 2SE engine do the same deal. Under a load, pulling a hill, the engine would lose power, then die. When you tried to roll it over, no compression. As it sat, it would come back and run fine. Start up again under heavy loads. It ended up being the guides were too long in the valve pockets and holding the valves open. The fix was to install new guides. But in your case, the sticking may be coming fromt he other end of the valves (spring end) and may be a result of varnish on the stem. The result was extra heat from the load, and the extra girth on the valve stem from the varnish and carbon. Carbon would be an issue in the valve pocket area just under the tulip, but as I said before, I bet your troubloe is the varnish on the spring end of the stem. Also, if you did do head work, do the guides have enough clearance? And if they do, is the engien overheating? So I think you are on the right track. Do report back with your findings. And you mentioned your waiting for the correct shims, if you are on the minumum clearance edge, as the engine warms up, it can also hold the vlaves open. Doesnt take much w ith little clearance. This would also explain the scenario you have.

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I’m glad you responded to this one Toy, you seem to be a good troubleshooter and ask lots of questions.

I didn’t remove the valves at all, just popped in the cams and checked the lash and piston to valve clearances.

The engine never got hot enough to kick coolant into the overflow.

I’m leaning more toward a cold related problem but I’m wide open for suggestions.

First I also thought that the tight valves got hot and closed up the clearance, and I actually packed snow around the engine to cool it down faster once I felt compression coming back. But, once I got it bumpstarted from the tow it didn’t run well until it warmed up. The second time when it started to loose power on the bay I was thinking that cold was the problem and I stopped and revved the engine sitting still and it cleared up after a minute or two, so I don’t think it’s heat closing the clearance. Also when it quit the first time I was just cruising at 60 on the bay, about half throttleish. The hour before that I was hitting deep snow and hills now and then which was putting the engine under a lot more load and never missed a beat.

The varnish on the stem makes good sense, but wouldn’t it also stick at high revs in a lower gear? Maybe the extra cold is gumming up the oil and combined with the varnish it sticks.

I have the new shims and am going to pop them in before the next ride. It was 2 intakes that were on the snug side so it may be that simple. I am fairly convinced that the piston was touching the valve when I tried turning the engine over. I’m surprised that it didn’t bend since there’s not much piston to valve clearance and I did coast to a stop in gear. This is one for Weird Science.

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