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912 Making Odd Noise after Re-Build

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Good afternoon. Over this past winter we rebuilt the K301 engine on our 912 Duetz-Allis. The engine block was sleeved and assembled with a standard bore piston and a 10 under rod. After completing re-assembly we used it for some light duty around the house. The engine ran well. A couple of weeks later I added the mower deck and started out to mow the lawn - mowing for about one hour. Upon finishing mowing the engine was making an odd squeaking/squealing/wheezing sort of sound with essentially the same frequency as the RPMs. Engine still runs well and appears strong, but sounds odd.

Checked starter to see if it was disengaging and it is.

Pulled plug and listened while turning over. The sound is still there.

If I put my finger over the vent hole on the breather cover the volume of the sound changes.

Pulled the breather cover and checked assembly. Assembly is according to manual instructions. Re-assembled, no change in sound. Checked valve clearance - clearance matches specification. Did not think to run engine with breather cover off.

I am interested to know if anyone ever had a similar problem and if anyone has an idea what either i did wrong or still need to fix.

Thank you.

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I am not sure with the Kohler engines, but I know with the briggs breathers the flapper inside that seals it can get gummed up and stop flapping. Might be worth looking at if there is a pcv valve mechanism of some sort.

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Finally had some time to spend with tractor this afternoon. Disconnected drive shaft to isolate engine. No change.

Removed breather cover and ran with cover off. No change.

Pulled head. Found that head is cracked. Will need to pick up a new head and start again.

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I am pleased to report that the new head is in place and remarkably the wheezing is gone. No serious running this evening, but the results of the new head are very promising. I will try to post a photo of the cracked head.

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