Tec HS40 Engine Internal Component Wear

[creia]

Update and epilogue:
I thought that some of you may be interested in what we ended up doing with this engine...
As it turned out there was more worn out than we had originally planned on, and a MUCH higher price to repair them than we had budgeted for...
Long story short- It would of cost $ 800.00 for parts and (machine shop) labor. As crazy as we are, and as much as we wanted to have an original numbers-matching engine, that is too much $$ even for us for this glorified lawnmower engine.
Replace crank (VERY limited production run/availability do to an extra long PTO end specific for the torque converter drive system)
New head (spark plug hole stripped)
Replace rod
Rebore cylinder .020" oversize, including .020" OS piston/ring set
Replace valve guides
Replace valves
Line bore block and install crank bushing on flywheel side.
My son is not sure what he will do at this stage. The value drops big time w/o the original engine. He may end up selling it as a "roller" (no engine). it has been completely restored/rebuilt by my son and all of the mechanicals have been redone).
Again, many thanks to all that helped!
Michael

[bgsengine]

What if you found a short block (NOS) for an HS40 and then clean up the crank and swap out crank and cam (if possible?) Just a thought...

[creia]

What if you found a short block (NOS) for an HS40 and then clean up the crank and swap out crank and cam (if possible?) Just a thought...

Brian,
That is certainly an option, IF, and only "IF" the shortblock came with the extended-length PTO crank. Good luck finding that- been there, done that, for quite awhile now! This particular HS40 engine was a very limited/special production run by Tecumseh (only a few years) made specifically for the Rupp mini-bike. The extended length crank (3" long as compared to 2.25") is needed to properly fit and use the torque converter variable speed drive system which adds a lot of performance (and not to mention VALUE) to the bike. We had high hopes that our existing crank could be repaired (they weld up the crankpin area then turn it down and polish it to the specs of the rod), however, we were informed that due to the small size (mass) of our crank there is almost a certainty that the crank will overheat and warp during the welding process. Basically, no shop will take it on. This process is done all of the time on larger cranks with very good success. How about finding a good USED crank you might say? Again, extremely hard to find and I would never purchase a crank I could not see and measure (Read: Micrometer the crankpin) in person- so that rules out an online purchase if we could even find one. Please don't misunderstand- Your idea DOES have merit (and is sincerely appreciated!).
***EDIT: One other "challenge" (requirement) with a short block is that it must be an older style points/condensor engine, as our engine has a "lighting coil/magneto" (this bike has headlight, taillight, brakelight) that mounts/bolts to the block in special threaded bosses that are not present on the newer style , electronic ignition HS40 engine blocks. - MRM
Michael

[creia]

In the interim since my last post, I kept looking for another engine. Amazingly, we were able to locate a used HS40 shortblock, with all internals including crank- the EXACT same model and year of our engine! The seller was kind enough to ship the engine to me at his cost and with no obligation to purchase (We have bought from him before), so that my son could take it apart and fully inspect and take precise measurements to check for any "deal breakers" BEFORE we bought it. The agreement was that we would put it back together and ship it back to him if we did not want it- what a great opportunity!! Fortunately, all that it needs is a new OS piston/ring set (which we already have), a rebore/honing (we have a good local machine shop that will do it for $ 80.00), and a valve job. That is not bad for a 46 year old engine and a BIG difference from the big laundry list of repairs our other engine needed that I posted previously. The 1970 Rupp Roadster restoration can now continue...
Michael