HS40 from 1969

#1
Question.

I have a 1969 Tecumseh HS40 with some broken fins on the flywheel.

I read that the 1969 HS40 had a different bolt pattern on the head than the 1970 and on HS40's did.

Is that the only thing different?
Could I use any other HS40 parts from any year and only need an early head?

Also, the fins on the flywheel have some broken fins. Will this be dangerous to run?
 
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markus

Well-Known Member
#2
not all 1969's had the small head, it was updated to the larger head that year, your best bet is to use your model numbers (if it all matches/original to block etc..) to verify what parts are needed. the general gasket kits they sell usually have both size head gaskets included though. You need to use your model numbers to order the crank seals and a few others...I think maybe the exhaust gasket, oil fill plug gasket/s

There were changes with the cam's into 1970 so lifters need to match what cam you use, and if your engine is from your Fox originally it was have an extended 3" crank like a Rupp, but it will be a bushing sidecover. You wont find that crank anymore so hopefully its still useable. I think you can still find a standard crank here there if its bushing though. The taper for the flywheel remained the same up through most of the 1970's. They updated the connecting rod bolts at some point too, put serrations on the flange of the head instead of using the lock tabs so you dont need to use that part on a new rod.

On your flywheel the "safe" answer is no. the aluminum flywheels ended for the HS40 when they made the changover to the wider square head shrouding around 1974
 
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#3
Good stuff. Going to use the block serial code very tightly.

So a far as the flywheel. I would have thought that if they made the aluminum flywheel up until 1974 & this is a1969. That aluminum would be stronger and fracture resistant than cast iron, which I assume is what they switched to?

Your saying the lack of safety of running a flywheel with some broken off tips on the fins would be incase there are stress cracks in the flywheel and it could break apart at higher RPMs?
 

markus

Well-Known Member
#4
Good stuff. Going to use the block serial code very tightly.

So a far as the flywheel. I would have thought that if they made the aluminum flywheel up until 1974 & this is a1969. That aluminum would be stronger and fracture resistant than cast iron, which I assume is what they switched to?

Your saying the lack of safety of running a flywheel with some broken off tips on the fins would be incase there are stress cracks in the flywheel and it could break apart at higher RPMs?
I think the switch over to steel was probably a cost cutting measure to help simplify production, but it made for a better wheel. The cast wheel does not have cast fins, there is a plastic fin assy that press fits on, so if they get damaged you just swap that part out. They are not interchangeable with the shrouding on your 1969 engine though, you would have to convert to the later shrouding and backing plate in order to use it.

And yes, cracks of course are something you would not want. Big chunked off fins throw balance out as well etc.. Thats something your gonna need to decide for yourself on.
 
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