Hs40 first timer

S

Sark

Member
#1
#1
Hello there! Working on a cool hs40 from a mtd I have. My questions are about the bore and what is considered bad/good. And what specifically I should do with what I have. The bore looks OK, and to touch except maybe one I can get a fingernail in. Should I just re-ring and try honing it. Never done either but somewhat able and I already bought a full seal kit. Also I know I need to clean and check the valves and lap, any good videos or explanations of that whole process?

Thanks for your help, this place rocks!
 

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creia

creia

#2
#2
While a bore that "looks OK" (i.e., no visible scoring) is encouraging, it really and truly is only part of the concern. Is it worn OVERSIZE, OUT-OF-ROUND, TAPERED, or ALL of the above.? These can only be determined by taking precise multiple measurements of the bore- top, middle, and bottom, and comparing those measurements with acceptable wear tolerances by the engine manufacturer. Just putting in new rings and honing if any of those 3 conditions stated above will accomplish NOTHING except lighten your wallet.
Michael
 
S

Sark

Member
#3
#3
Ok so any tips or videos on you can point me towards, Im here to learn. When you check this how often are they bad percentage wise? Also just wondered what people who rebuild these just think of my hs40 and it's condition from an outside but educated perspective.
 
creia

creia

#4
#4
If you are doing any work on Tecumseh flatheads this is a "must have":
New Tecumseh Technician's Handbook Manual Part 692509 | eBay
It will have all of the information you need. You can probably find it for free on the internet, but I always prefer an actaul manual I can hold in my hands. My son and I have referred to this manual MANY times.
Michael
***Edit: The online link to the repair manual is already on this forum! Just go to the top of the list of Tecumseh threads and it is the first "Sticky" listed- It was posted by KustomKartKid
 
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S

Sark

Member
#5
#5
Ok so have removed valves, the crank, piston and rings. The cylinder I'm guessing has too much scoring as well as the piston. The crank and rod looked fine where they go together no scoring,but the crankshaft keyways on both sides are worn. After I check for taper,out of round I'm planning on ordering an oversized piston and rings and new crank after i have it bored over. I'm sure I could look for something needing less work or $. But I am interested in this motor for the mtd I'm resureecting and figure might as well just pony up and learn on this one.

How do I figure out which parts for my specific model? Anyone in North seattle have a machine shop they recommend?
 

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OND

OND

#6
#6
Hey Sark, I'll help you out the best I can. Cylinder and piston definitely got some scratches that need to be addressed for sure. Heres your pic of the serial/model number.. that will help you find the right parts to fix your engine.



Serial # 0314 means your engine is a 1970 model built on the 314th day .
 
OND

OND

#7
#7
Model # on Partstree will give you the correct Tecumseh part # for the piston and your other parts. But they are not showing nothing for your engine except the stock piston ...010 and .020 oversize pistons are not in stock.
 
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creia

creia

#8
#8
Do not order an OS piston ring set until you get PRECISE measurements of the cylinder bore! Take it to a reputable local machine shop that works on small engines and have THEM measure it and tell you what size OS piston/ring set to get.
Michael
 
danford1

danford1

#9
#9
Also, ask a machine shop exactly how much it will cost to bore and hone it. Add that to the piston, rings and gasket prices. You might find that the cost to rebuild it are more than a good running used engine cost ($50 -$100). If you are a purest and Only want the original engine on your bike, then just open your wallet and go for it.
Before you order the parts, call and talk to someone that will check if the parts are actually in stock and ready to ship. I got burned to many times by websites that indicate they have the parts in stock when they don't. You might think you will have your parts in a couple days when it takes Weeks for them to back order them then another week or two before before you get them...
Just my opinions, others will vary.

Danford1
 
Dr. Shop Teacher

Dr. Shop Teacher

#10
#10
Looking at your pics, there are a couple of things I'd do before I opened up the wallet for big expenses.

First, head to a small engine repair shop with your engine info, and get the correct flywheel key for the engine. Looks like the wrong key had been used (or a steel one) and jammed in previously. You need to see if the flywheel will lock in place on the crank. If it moves (or wobbles), then you might have issues keeping it in time--these points engines are very finicky and a couple of degrees off either way will hurt. If the flywheel "locks" ok, then in my view the crank is salvageable provided you don't have scoring on the bearing surfaces. The PTO side doesn't look too bad, I've had cranks with some excess drilling for set screws.

Second, you've got some scratches on the piston skirt. Pics don't tell the whole story, so try some fine steel wool and a lubricant, and see if they polish out. The point is to see how bad they really are. You should also use a digital caliper with long arms to measure the piston OD on multiple axes. The Tecumseh manual will give a reject size. Tool: Search results for: 'caliper'

Third, cylinder wall scoring. Steel wool is NOT the way to check here. Micheal correctly suggests checking to see if it's out of round. Use the caliper referenced above and a telescoping gauge. You can take multiple measurements as shown in the Tech manual. This should give you a good idea if the bore can be saved. Then, you could hone the cylinder to see if the scratches diminish. Telescoping gauge: Telescoping Gauge Set 6 Pc

You'd need a good cylinder hone kit to go any farther forward. I'd invest $25 for a couple of must have tools for the tool chest and a key first. E-bay is remarkably dry for HS40 parts currently.

Hope this helps you get started.
 
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Dr. Shop Teacher

Dr. Shop Teacher

#11
#11
Another quick and easy thing to do before spending lots of money is to check the ring gaps from the current piston/rings. Carefully remove each ring (spread very gently with your thumbs and work out, up and over), tag each in some way so you know the order and direction (which side faces up) of the ring. Slide one ring into the bore and using the piston, push down the bore. Measure the piston ring gap in multiple places on the bore using a feeler gauge. Do this with each ring.This will give you another measure of whether you'll need new rings, or an oversize piston, rings and boring. The manual gives you the reject sizes for rings.
 
S

Sark

Member
#12
#12
Thanks guys. Will head out and grab those tools this week. I will check the ring gaps and try polishing the piston and report back. For me this project is more about expanding skills than the money spent. I like working on old motors like outboards,mowers but so far have mainly just messed with carbs and fuel system issues vs more complex work.
 
S

Sark

Member
#13
#13
So if I'm reading parts tree right for my model there is an .20 oversized piston and rings set tecumseh 35546 for $61.20 doesn't seem too bad.

Definitely had wrong flywheel key... no cutout.
 
M

metal man

New Member
#14
#14
Dr. Shop Teacher said:
Another quick and easy thing to do before spending lots of money is to check the ring gaps from the current piston/rings. Carefully remove each ring (spread very gently with your thumbs and work out, up and over), tag each in some way so you know the order and direction (which side faces up) of the ring. Slide one ring into the bore and using the piston, push down the bore. Measure the piston ring gap in multiple places on the bore using a feeler gauge. Do this with each ring.This will give you another measure of whether you'll need new rings, or an oversize piston, rings and boring. The manual gives you the reject sizes for rings.
Click to expand...
not to much to learn from the rings but there state. Got a motor cylinder good piston good clearance on the high end but will run good with new rings . But the rings are toast ,so ya take it as it is. Piston to cylinder fit and shape have all to do with redoind a motor . As for cost even if its too high for you pass the motor on .to high for you ain't bad to someone.
 
Dr. Shop Teacher

Dr. Shop Teacher

#15
#15
metal man said:
not to much to learn from the rings but there state. Got a motor cylinder good piston good clearance on the high end but will run good with new rings . But the rings are toast ,so ya take it as it is. Piston to cylinder fit and shape have all to do with redoind a motor . As for cost even if its too high for you pass the motor on .to high for you ain't bad to someone.
Click to expand...
All true...my point was to save him some cash before the big expense of going to a machine shop and being told the same thing for 50-80 bucks in shop time. If the rings had really wide and varying gaps in varying parts of the bore, then yes, bore it to oversize and not waste time/cash on other measures. The H60 I just rebuilt had funky ring gaps but the bore was true. By asking on the forum, I learned this was not uncommon. An oversize ring set was my fix.

To the OP, the 020 piston ring set is priced pretty good. Do some shopping though. Floyd's and Sidegrinder on eBay are good sources of used Tec parts.

Endows.com is another vendor that sells NOS OEM parts. You need part numbers for them, though. They sell it but don't really know what it is.
 
S

Sark

Member
#17
#17
Ok, spent a little time working the piston with some steel wool, don't think it's reusable. Measured the ring gaps on all three rings, top two were close to the same end gap, but the bottom one considerably larger end gap pic with 5 feeler Guages showing. Closer pic of piston crank and rod journal ( I think). Thanks for pointing me to another set for the piston. I should be able to grab the tools I need tomorrow or thursday to check the bore and I found a machine shop right on way to work that rebores aluminium, still looking for local small engine shop. Will post once I check out of round etc.
 
Dr. Shop Teacher

Dr. Shop Teacher

#18
#18
You did some good work there. Piston is shot...the lower ring is the OILER ring and since it had a huge gap, your bore is most likely no longer true. Piston bearing surface shows wear--of more interest is the piston journal on the crank. If it has light scratches (seems to show minimal wear from piston rod bearing surface) and polishes up ok, then I'd say reuse it (some will scream at me). If it has grooves and high edges--more money on a new crank. It just depends of whether you plan on running the engine wide open all day or do as I do: ride 'em around and have the neighbors wave.

Edit note: I've been re-reading my posts before submitting and missed this one. Woke up at 3 am with an Oh, S%#t. Damn pain meds!
 
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creia

creia

#19
#19
Check (measure) your clearance at the crank to rod journal and compare to factory specs. Is this engine ball bearing crank supports at each end or is it just a bored bushing hole in the block and case cover? If the latter, inspect it carefully for scoring or excessive play/clearance. My son just went completely through a 1970 HS40 that was OEM on a Rupp Roadster he is restoring. As it turned out EVERYTHING was worn out(even the valve guides). While it COULD be rebuilt, it was unbelievably expensive to do so. He searched and searched (took about 6 months) and found a complete used HS40 short block (same model # and era) that was in very good shape. All he will need to do is rebore and install a OS piston/ring set, and install all of the tins and carb from his original engine at a fraction of the rebuild cost.
Michael
 
OND

OND

#20
#20
Good advice Michael ! Also I'm with Dr. Shop on the piston it should now be used as a paper weight. Shoot us some pics of the rod journal on the crank and of the block and side cover where the crank rides.
 
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