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Old 06-11-2009, 08:55 PM   #1
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Default It got Hot! Engine Wear?!

After a recent clutch repair, my OS .21TM tune has been way out, and I havn't been able to get it even close to acceptable. I have read the tuning bible, and I believe it may have solved my troubles, but before I go ahead and run/tune this engine I was wondering what 'wear' or 'damage' looks like or if it is even visible. Long story short the temp gauge is showing a max of 324.4F was hit, probably when the clutch went and the engine wound out with zero load.

Here are some pics of piston, sleeve, and head. They look clean and OK to me, but I really have no idea what I am looking for.

Any thoughts? Is 324 = engine death, or might it be OK? What exactly fails from heat, does the con-rod and crank fatigue, or is it usually a lack of lube that causes the piston to seize? Sleeve and piston look clean and un-scarred.

Also how much play, if any should be between the piston and cylinder wall? Compression when at ~200F doesn't feel like much. I can turn it over with my finger fairly easily. Normal?

edit- I should also add that that is the same plug, it isn't deformed and still glows like normal.
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It got Hot! Engine Wear?!-20090611_4683.jpg   It got Hot! Engine Wear?!-20090611_4686.jpg   It got Hot! Engine Wear?!-20090611_4688.jpg  
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Old 06-11-2009, 09:47 PM   #2
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I'd be worried. Take the motor to a shop or a person who knows what there are doing.

Good luck.
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Last edited by gotspeed_2000; 06-11-2009 at 09:49 PM. Reason: took another look at the post
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Old 06-12-2009, 06:13 AM   #3
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Look very clsely at the sides of the piston and the inside of he sleeve. If there is scarring then you have damaged them and they may need to be replaced. Head also destroys bearings. If you are chasing a tune check and see if he front bearing is leaking at all it will be wet around he bearing. I have had front bearings spit gas out the font. That will never allow the engne to hold a tune. Check the piston and sleeve and replace the front bearing that might be enough to get you back in business. On these os engiens I like to keep them at 240. Some say 260 is ok. Just make sure there is good smoke out of the pipe and you are good. Anything above 260 is too hot in my opinion.
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Old 06-12-2009, 06:21 AM   #4
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Its doesnt look to bad but there is really only so much you can tell from pics. Put it back togeather and see how she feels. Yes you did get her to hot but that doesnt mean its dead, the main thing that happens from overheating is compression loss. Put it back togeather and see of the compression feels, then run it and get come heat in it and again feel the compression. How many gallons were on the motor before the overheat?
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Old 06-12-2009, 09:23 AM   #5
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3/4 of a gallon on the engine before it overheated.

Compression feels fairly tight when cold but a fair bit less when hot. It is hard for me to explain that.

If it is leaking out the front bearing, that would be getting the clutch wet, correct? Rear is the pull-start? I imagine either bearing leaking would cause the same problems?
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Old 06-12-2009, 10:55 AM   #6
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Quote:
Originally Posted by Orangetang View Post
3/4 of a gallon on the engine before it overheated.

Compression feels fairly tight when cold but a fair bit less when hot. It is hard for me to explain that.

If it is leaking out the front bearing, that would be getting the clutch wet, correct? Rear is the pull-start? I imagine either bearing leaking would cause the same problems?
Only a front bearing can leak. Rear bearings are in the center of the engine, and fully incased in the engine. The front bearing is the one you can see at the front/clutch side of the engine. A rear bearing can cause issues, but not in the same way that the front can. If it is still pretty tight when cold you should be OK. Any engine will have less compression at running temp. If you have leakage by the pull start you may need to seal the backplate, or it could simply be a blown exhaust gasket.
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Old 06-12-2009, 03:53 PM   #7
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Exhaust gasket is leaking. Maybe it could be giving me grief with my tune (uneven fuel pressure?). I picked up a couple of new ones, though they never seem to fit properly. I have a trinity racing pipe and it just doesn't seem to fit over the TRX3.3 or OS.21 exhaust port very well. Any gasket advice? Can that cause an engine to continously overheat and lean out, stall? It seems to start, idle, and go fine, but only seems to run lean and hot.
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Old 06-12-2009, 10:49 PM   #8
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It's ok you didn't kill it as long everything turns and not scored up you are fine. You didn't really shortened the life of the engine. I hit 300-310 with my Picco 26 in Savage all the time just the nature of monster truck. It didn't kill it wasn't burning the plugs or scoring the piston and sleeve.

I've even had it once in practice the fuel filter 1/2 plugged. Going down the straight-away I gain 2hp more pulled a wheelie flipped it on it top so hard that it flipped itself back on it's wheels and went to fast idle in the Savage. Temp was 425 had a hard time shutting it down. I checked it it was fine one of the reasons why I won't inline fuel filter anymore
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Old 06-14-2009, 10:19 PM   #9
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Thanks for all the replies, it seems to run still. Has enough compression to really rip, but I can't get it to tune at all. I think the carb is having issues or something. I'll start a new thread for that since it's unrelated.
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