Shock cooling the engine--fact or myth?

[Kodatech]

Originally Posted by Tab B.

Well fellows, shock cooling can have an adverse effect on the right engine. I saw it happen. Back in the early 90s a friend of mine had an RD400 "Daytona Special" {2 stroke!!!} rebuilt. I was on my 86 gixxer, and we were just out for a ride to sort of break in the RD. It was in the high 30s to low 40s{F} We did a roll on, up to about 80 to 90 mph. When we backed out of it, a couple of seconds later, I heard a screech, and looked at my friend. I could see BIG eyes in his helmet, as he coasted over to the breakdown lane. He yanked the clutch in before he could do the rear tire skid from hell. He had never had this happen before, and was really bummed that his fresh rebuild did this. I told him to relax for a minute, and follow my hunch.
I guessed that on the roll on, the engine as a whole got warm, and expanded together. Then when he shut it down, the cylinders shrunk around the still hot piston. She was a bit tight I guess. He was sweating getting the bike home. After a bit, I told him to kick it over, it'll start. {pretty sure of myself eh!} Sure enough, it started on the second or third kick. The fact that it kicked over at all had my friend smiling. So yeah, shock cooling can happen, but probably not very damn often.

I think I would have had to change my pants after that, but I couldnt help but notice you said his fresh rebuild did this. I am not saying that it DIDNT "shock cool" because I wasn't there, and if you say it DID, then I have no reason to NOT belive you. However, I think a more likely explanation would be that the new rings and new cylinder did not have enough time to properly break in and seat. I just think this was more likely the culprit, than the phenomenon noted in the first post. That being said, I think something similar happened. We all know that the sticker that comes with new motorcycles for a "proper" break in is important to the longevity of the bike's engine. What the sticker DOESN'T tell you, is that the reason they tell you to shift and ride like that is so that the engine stays at a constant temp. during break-in, so the rings and cylinder bores can seat and sort of wear to eachother. I think with the fresh engine, the sudden increase in engine tempurature, followed by the blast of cold air is what happened here. So yeah, I guess it DID "shock cool" itself to death, but I DON'T think it would have happend on an engine that was already broken in.










But....I wasnt there...

[murphyslaw1978]

Shock Cooling: Myth or Reality?

[eb77k]

I have seen a similar situation. I was late to meet my buddies at the lake for some ice racing. I knew you should really get your stuff hot before pounding on it. Being late and all, I couldn't stand seeing myself not handle bar to handle bar in the mix. Needless to say by the end of the day I was hearing alot of noise from the engine.

I took the top end apart and the piston and cylinder was all torn up. After taking the engine parts to my engine builder for advice he shook his head and simply stated "cold siezure." The piston grew alot faster than the cylinder as the motor warmed up (at about 8000rpm). The piston skirt collapsed by about .060 0f an inch. The noise was piston slap.

OUCH! New piston with custom flycuts to match moved and enlarged valves in the head, ceramic coating on dome, moly coating on skirt: $335.00 gaskets: $45 cylinder bore $60

I had to put it together with the engine builder watching. Humbling to say the least.

[kay]

My Kawi is air-cooled and I've ran it at redline for quite a while (on a track, not on open road) but it was OK. Well, I never knew about this potential (or is it?) problem anyway.

BTW, talking about tractors, I've seen a guy do a wheelie on his tractor!!! Quite crazy but of course, it was not on open road either. He did it in his field.

That was a sight to see though!

[Colorado Cajun]

I would say you are thinking way too hard while being out on a ride. Enjoy the ride a little more.

[PhotoJoe]

Originally Posted by eb77k

I knew you should really get your stuff hot before pounding on it.

[mike-s]

two things,
1) look up "tractor racing" there are some INSANE creations there
2) another possibility Tab. B. is one that used to affect 2 stroke gp bikes (still affects the 250's) where when they roll off the throttle the lack of lube on the already highly tuned and minimally lubed (more lube=less fuel) engine seized due to oil starvation. Definately likely as the rebuild was brand new.

[Tab B.]

Originally Posted by mike-s

two things,
2) another possibility Tab. B. is one that used to affect 2 stroke gp bikes (still affects the 250's) where when they roll off the throttle the lack of lube on the already highly tuned and minimally lubed (more lube=less fuel) engine seized due to oil starvation. Definately likely as the rebuild was brand new.

That is a real good one. Didn't think of it myself. Since the RD has oil injection into the carbs, that might explain a lot. My old Suzuki T250 had injection directly to the main ball bearings. It never seized up on me.

[Rickster]

That shook some dust loose on my memory too. Back in the mid 70's, I had a 250 Ossa, Phantom that I would sometimes take out on the lakes in the winter, and terrorize the snowmobilers.

Running across the flat surface of a ice, and snow covered lake, you would sometimes be able to hold it wide oben for quite a ling peroid of time, and every once & a while, it would start to try and sieze up on me. It would do this thing, where it would sieze, and release, over, and over again, till I let off the gas, than it would be OK again. I always thought I was just holding it open for so long, that it was running out of gas, but looking back on it now, I realize that I was probably shock cooling it.

[Tab B.]

She also could've been some squeeky lean. Although, that might be a stretch. It might hole a piston if it was too lean. I never quite got the hang of those old fussy 2 strokes.