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560Dennis

Tecumseh 8hp HM 80 Head Bolts

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Snapped three bolts getting the head off of this Tecumseh . Writing this in hopes maybe it will cause you less grief. 

The Ariens SnoThro engine would run good for about half an hour and start to stall. I had to adjust the needle valve on carburetor as it would run . At night the muffler would glow red. And fire was coming out the exhaust. 

Hints from other sites suggested valve Clearence . 

So just before the season I started to in vestigate . 

I went to remove the head bolts out the aluminum head and block . The motor was cold , The bolts snapped red circled . The one we had to Helicoil, the others threads were saved by putting it on a vertical milling machine and end milled the broken bolt out. 

So next time I would or say I  reccommend try to use map gas torch on the block around the head bolts to get them to expand to help get the bolt to release. Safety first clean oil and remove carburetor. Any way 

Back the reason ,the exhaust valve I measured with feeler gage to have only 3 or 4 thousands Clearence. , so we reground valve surface and lap them in , to get as close to ten thousands Clearence intake and exhaust. Oh measure the valves on litle past top dead center also to make sure the decompression cam don't inter fear with measuring the Clearence. 

Let you know how this run in a few days ,,cutting it close ,going to need the machine soo. 

Im glad I looked into this ,cause the machine had a bearing failure on out pout shaft and the friction drive hub had cracked so in pretty lucky that we got to get this back together before a serious snow comes in off the lake . 

its a puzzle why that exhaust valve was set that close . I don't remember putting  new valve in it . I also wonder if the new gas without lead hammer valve into block , but the valve seat looked good about .05 inch 

any. That's the Tecumseh story 

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As any thing that's 45 years old the Tecumseh exhaust valve had 👀.005 Clearence so my son made a new guide . Lapped it ,  

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