HS 40 punch out

bbiggs54

Active Member
#1
Need some help, the motor on the grandsons Cat needs some work. The piston needs to be replaced with a 20 or 30 over size and the connecting rod as well. I know where and can get the machine work done in Ann Arbor, just need to know if these parts are available. Also help with the decode of this motor plate. I believe this is the original motor to this Cat eliminator, any help would be appreciated. Thank you 20200813_141057.jpg
 

markus

Well-Known Member
#2
Yes, that engine is from a Cat, I converted one to a slightly different setup/color for someone a few years back. That one originally used the L shaped rear exit muffler and the choke lever above the air filter as it predated the Taylor style muffler systems, we set this one up for the later taylor muff and correct choke lever that was created by tecumseh to clear the header: project Jacko HS40 which you can see an original setup on MJ's bike in the pics

Problem with oversizing them is finding the parts, Tecumseh only offered up to .020 over and if you get into one, if you can even find it, are not cheap. Wiseco did offer back in the day .040 and .080 over setups but those are a bit of a rarity anymore, I have never seen or had a .040 but I have had a couple of the .080 setups come and go through my collection over the last 10 years. I have a few .010 pistons in stock that I bought in a parts buy, but sounds like your probably past that measurement. The part numbers for the .020 overs are 34853 for the old style and 35546 for the later style thin ring version.
 

Gdiddy58

Active Member
#3
You can Google the model#, choose Jack's small engines, and use their parts breakdown to get part numbers then go to eBay but it might take a while to find a 20 over piston set.
 
#4
I didn't find any when I looked last night, but they do come up. I'd like to remind you of the fact that these lawn mower engines, and even new, were in some cases not built up to the specifications cited in the manuals. If it comes down to losing a bit of compression or not having an original engine at all, it's an easy choice for me. I've also used OS rings, gapped down on original pistons. Good luck with it, and you and your grandson have done a great job on that bike!
 
#7
If you do not have precision measuring instruments (and know how to use them) its best to take your block to a reputable machine shop and have THEM tell you how much oversize it will need to be bored. That being said, I believe you will have great challenges finding a complete Tecumseh O/S piston and ring set. Watch out for any "NOS" (New Old Stock) sets you see offered for sale (eBay) as many times they have been repackaged with some OTHER piston/ring set or mismatched/missing rings even though the box shows the correct number (been there, done that!) Dave's trick (filing down O/S rings) is a good one and is a viable and legitimate solution, however, that's only good for up to a .010" O/S ring on a standard piston- and you still need to locate a .010" O/S ring set. Both your piston and cylinder look significantly scored. I do not think that O/S rings alone are going to do it- you need a rebore.
Michael
 

bbiggs54

Active Member
#9
Thank you for the advice Micheal, I will take to the rebuilder that did my Briggs for the 400TS. It cost me a bundle to do that engine as it was scored similarly. I was hoping to assemble it myself and save some money. The parts for the briggs engine were available.
 

markus

Well-Known Member
#11
Yeah I saw that, but I know where to take it to get it turned. Just need the correct connecting rod and piston, which someone will need to tell me.
I supplied the part numbers for the oversized piston in .020 in my other post rod you want is a 32875a, that part number is latest version with the most updates to the design for best oiling etc.. they do not make undersized rods unfortunately that engine used the standard service crank so those I believe can still be found new if it’s too far down or cost to fix is higher than new. Just make sure it has the cut out ( will look like someone stuck it on a bench grinder just next to the rod journal on the out put side. That is there to clear the big lobe on the compression release camshaft that engine should have. It should be on the crank, but if it’s newer made stock there is a possibility it is not as they dropped that cam design during 1970.
 
#12
Need some help, the motor on the grandsons Cat needs some work. The piston needs to be replaced with a 20 or 30 over size and the connecting rod as well. I know where and can get the machine work done in Ann Arbor, just need to know if these parts are available. Also help with the decode of this motor plate. I believe this is the original motor to this Cat eliminator, any help would be appreciated. Thank you View attachment 267715
who does your machining work in Ann arbor Thanks Dale
 

cfh

Well-Known Member
#13
if it was me (and clearly it's not), i would find an HS40 Tecumseh snowblower points/condenser engine. i just saw one on facebook for $40. Use that as your core long block. Then transfer your bike specific parts to that long block (flywheel, motor tins, exhaust, carb, etc.) It would cost a lot less. sure you'll have to re-paint the block (probably), but that's pretty easy compared to finding all those parts and having everything bored and re-done. You're gonna spend big money otherwise.
 
#14
At this point, I'd seriously consider getting another points engine and swapping the shroud and ancillary equipment. You'd have to mess with timing if you were to do a proper refurbish on a replacement, but you're already into machine work on the bore, nearly unobtainable parts, and what parts you can find, like the crankshaft will be costly. If you were to repaint the block and use some "antiquing" methods, you wouldn't have to paint the shroud, and keep it looking original.
 
#15
Yeah I saw that, but I know where to take it to get it turned. Just need the correct connecting rod and piston, which someone will need to tell me.
Having a crank "turned" will result in a crank journal that is undersized and you will need an undersized rod which Marcus has already correctly pointed out that Tecumseh never made. The crank journal to rod clearance is critical- "Plastigage" (Google it) is your friend in this regard.
Michael
 

bbiggs54

Active Member
#16
if it was me (and clearly it's not), i would find an HS40 Tecumseh snowblower points/condenser engine. i just saw one on facebook for $40. Use that as your core long block. Then transfer your bike specific parts to that long block (flywheel, motor tins, exhaust, carb, etc.) It would cost a lot less. sure you'll have to re-paint the block (probably), but that's pretty easy compared to finding all those parts and having everything bored and re-done. You're gonna spend big money otherwise.
Would you be interested in taking on this engine project? I'll have to get you the name of the machine shop. I can tell you it's in a strip across the street from Costco Ann arbor.
 

bbiggs54

Active Member
#17
Having a crank "turned" will result in a crank journal that is undersized and you will need an undersized rod which Marcus has already correctly pointed out that Tecumseh never made. The crank journal to rod clearance is critical- "Plastigage" (Google it) is your friend in this regard.
Michael
Yep that's what I had done to the Briggs and was able get a manufacturer undersized rod. Good info, didn't know they don't exist for the Tec.
 
#19
Yep that's what I had done to the Briggs and was able get a manufacturer undersized rod. Good info, didn't know they don't exist for the Tec.
You can get the crank journal welded up and turned back down. I've rebuilt about 30 of these engines, and never yet had to throw one away. The last one I built went on a Lil Indian, and I was able to procure a .020 over piston and ring set. You can also send it in to get a nikasil plating job on the bore.

@delray has a reliable contact for doing the crank shaft work, as well as the nikasil work, since it seems you're determined to go with the expensive route. (grin)
 

bbiggs54

Active Member
#20
My buddy tells me one of the last 4hp Tecumseh's made (he called them"powersports" ) says I should find one of those. Will my recoil cover fit on this?
 
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