pumped 61 new engine seized

[yesandbut]

This engine is rather old, has a perry pump and carb, and was run on the bench at least 20 years ago and put away until last week. I ran a few tanks through it very rich, starting and stopping to cool, and started flying it in a breaking lean rich sound. It seized during a low speed pass, just off idle. The seal area just behind the front bearing shows galling. Everything else looks good, including the bearings, but the front bearing may be a little loose, can you tell me the proper clearance so I can check it? No signs of overheating. There is some varnish around the bearings though. The only thing I can think of is the varnish kept lubication from getting to the seal area and front bearing. Does this sound reasonable? Any help you can be on the bearing clearance would be much appreciated.

Best regards,
Chris

[MECOA]

You should be able to just polish the crankshaft and remove any gauling from the case, as little as possible. If the fit becomes too big it will leak fuel out the front. .003 total clearance on the dia is the most you would want.

[yesandbut]

Thank you for answering my post. I'm not sure what clearance you gave me, I was refering to the bearing. I got a bearing from my local hobby emporium, a 6525 series 72 which is the same dimensions, but has a grey metal ball cage, while the original looks like brass. The old bearing has .002 inch dia. clearance, and the new one .001. Ran a few tanks of superfuel through the engine rich, and it seems to work great! Any warnings or mistakes?

Best regards,
Chris

[MECOA]

The bearing does not seal the crankshaft on a model engine. Big 2 strokes have a rubber seal but not model engines.

read this and you will know what I was refering to.

http://www.mecoa.com/faq/crankshafts/blowby.htm

[yesandbut]

Lots of great information, thanks. One final question. What caused the galling of the seal area in the first place? My thoughts are that the excessive clearance in the front bearing allowed the shaft to rub on the crankcase. Do you agree?

Thanks for a great website.

Best regards,
Chris

P.S. Is there anything wrong with using the old style (series 72) bearing?

[MECOA]

More likely FOD. Some small piece of something probably started it and once it starts, it doesn't stop. The bearing should not have too much radial clearance.

[yesandbut]

How much is too much clearance?

[MECOA]

More than .003" but if it runs good and doesn't leak out the front while it is running, don't worry about it.