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1985 Craftsman 18hp compression good???

irp's Avatar
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08-02-04, 07:18 PM   #1  
1985 Craftsman 18hp compression good???


I recently acquired a 1985 Craftsman lawn tractor model# C459-60418, K1850, S/N 41-026-9480. Motor is a Briggs & Stratton 18hp twin 422700 series. I'm curious what the proper engine compression should be? A dry compression test yielded (left) - 105psi, (right) - 108psi. After squirting some oil in each cylinder the readings changed to the following: (left wet) - 110 psi, (right wet)- 112psi. Are these compression readings still considered to be acceptable? How much life left in the engine before an engine job is in order? I haven't owned it very long however I don't believe the engine burns oil. It also runs great. The previous owner took very good care of the tractor and changed the oil regularly (known fact).

P.S. What grade of oil would be better to run in the engine for maximum engine wear protection, 10W-30 or 10W-40???

Thanks in advance for any replies given.

Brian A Irwin
SSM, ON, Can.

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Azis's Avatar
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08-03-04, 12:18 AM   #2  
Compresion on most small engines can only accurately be tested under well better than average conditions. There may now be some standard with larger and twin engines, but I have yet to find any. Older Briggs manuals say to check by a "rebound" test, which is, turning the engine by hand Oppisite normal rotation direction, feel when the piston is coming up on compresion (actually power stroke in reverse) just b4 it would go over release the engine and there should be a slight rebound.
Although from the testing I have done on some single cylinder engines, (65psi..or so) I would say your #'s look good.
As for oil, its best to use 30W in most conditions. Depending on your use and your Climate you may warrant a multi grade if you intend to use it often during the winter, and multi grade should be checked and changed more often.

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08-03-04, 01:39 AM   #3  
Hello Brian!

I agree with Azis. The compression readings are great, and there's no indication by your information that leads me to believe any engine rebuilding will be needed in the near future. If the mower will be operated in warmer weather, use straight 30w as suggested. When used in temps below freezing, 10w-30 might do a bit better.

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