Hs40 Build

[davidcmay]

Hello All,

Rebuilding a Tec 55265D SN/ 0257 for my '70 Lil indian 5000.

The donor motor was a Ariens snowblower and has a PTO and I would like to remove it. Suggestions are as easy as the hack saw method, but i'd like to make is a little more OEM looking.

I have never run this motor, but after disassembly found it to be super clean inside and even some cross hatching on the cylinder walls.

Questions are can I cut down a cam (compression release) safely on a lathe?
Bung the cover until I can find a replacement?
Invest in a billet rod and new piston and rings? Remove governor?
Valves and springs?

I did a basic cleanup + regasket rebuild on a H35 and an HS50 with great success and feel comfortable going to the next level.

Any suggestions would be great!!!!

Dave

 

[cfh]

i assume you mean there's a 2nd small PTO and you don't want it. You can remove the cam and cut it to a length of .6". you do not need a lathe to do this. A hacksaw is fine, and then a little grinding to make it smooth. look at the original cut... they used a bandsaw at the factory! you will need a 7/8" plug for the side cover, or a new side cover.

This info is covered here...
http://www.pinrepair.com/minibikes/tecumsehmb.htm#pto

 

[Havasu Dave]

Your questions:
Can I cut down a cam (compression release) safely on a lathe?

Yes, and you can remove that bump with an angle grinder. You won't feel a heck of a lot of power increase. If any. Look in to getting your cam modified by Tim Isky. (310)769-6880 Or, you can maybe find one of the Dyno OHH 245's around.

Bung the cover until I can find a replacement?

OldMiniBikes Member Rick Chatten posted the information here, and cites it as a 7/8 freeze plug. I see no reason to cut off a PTO cam shaft. It doesn't even show once you have the clutch mounted. There are probably members right now who have HS cams and covers just taking up space by the way. If you want to change them, put out a wanted ad.

Invest in a billet rod and new piston and rings? Remove governor?

The rod is the ARC 6282 Billet Rod for the 5.5 OHH engines. Replacement rod is the best engine survival investment you can make. It is the achilles heel of a Tecumseh.

I've never replaced the piston, but I do check the skirts against the manual.

I get the rings from Ebay usually. Don't bother ordering any until you've measured and corrected your bore. I like to shoot for the minimum end gap.

Yes, you can remove the governor once you get that new rod in. I tap for 10-32, and drive a machine screw in with Loc Tite 620. (green) Remove the spool from the block as well, but you can leave the shaft.

Valves and springs?

For stock RPM ranges, stock valve train is fine. Delray did some work and found that the components below work just fine, although the spring retainers needs to be modified to fit the spring. I used my drill press as a lathe, since I don't own a lathe. Not a problem.

Dyno AN-001 18 LB valve springs for the Briggs Animal.
Briggs DCSH103 valve keepers for the Flathead.
Briggs DCSH102 lower valve spring retainers for the Flathead.

If you do all of that work, you're going to want to ditch that Tecumseh carburetor. You generally have to make your own intake manifold. I've seen some folks use the original with some cobbled up adapter on the end, but that just impedes flow, and looks ugly. There have been some manifolds cast that will fit a Mikuni to an HS. At that point, you will need to incorporate a vacuum nipple from that manifold (best) to power the fuel pump you need because the OEM manifold and carb sits low enough for gravity feed.

I built one of those engines for a project, but didn't document it much, since others were doing the same thing. This test video is the first time I started the engine, and I changed jets and experimented with the metering needle. Carb is Chinese Mikuni, VM22.

Those of us who built these engines used bearing PTO cranks and side covers. They are superior in handling loads over the "recreational" bushing engines. Delray actually machined the crank and block for the mag side as well, resulting in a superior rotating assembly. But you can get by with a bushing engine. Just like you can get by with a totally stock engine. It is also possible to machine a crank to accept a bearing and fit a bearing side cover.

Look up Delray's work on that, or he can chime in. @delray Also, @OND might have some interesting solutions on powering lil Indians.

 

[cfh]

Davidcmay, most of your questions are answered in the document i posted
http://www.pinrepair.com/minibikes/tecumsehmb.htm

The arc 6282 connecting rod that H.dave mentioned is a good idea. It's $65 though. don't know your budget. personally i don't generally use the Arc rod, and i do remove the governor system from my Tecumseh engines. My right hand becomes the governor. If you're letting other people use the bike, this may not be a good approach. In that case the Arc rod is good $65 insurance.

On the ball bear versus bushing side cover... my opinion is this is over-rated. I had a minibike all through the 1970s with a Tecumseh HS40 and a bushing side cover. I wasn't able to kill it (and man i tried.) Really only Rupp TC1 bikes and maybe some other random makers used a ball bearing side cover during the hey day of the 1970s. The majority of those mini bikes used bushing side covers. Again it's an opinion (right or wrong), but i don't put a lot of emphasis on ball bearing side cover motors. Now if you're driving the thing to Florida, ok you probably need it. But let's be frank... we're all old men and we're probably not beating the crap out of our old Tecumseh engines... because if you were, you would have a "stage 9" predator motor with billet everything and a mukini 99 carb and four on the floor.

That said i do like to do some mild mods to my Tecumseh motors. I do remove the governor assembly. And i like to use a slide style carb. and i like a cool looking exhaust. But i don't go much past that. You'll get a bit more performance doing that, at minimal cost. Though i do have one of those Dyno cams, i haven't installed it. Mostly because i've heard it makes the motor difficult to pull start. And i like my shoulder the way it is. Again i'm an old man. If i was some young punk i probably would be modifying a Predator motor, and not some 1970s Tecumseh flat head! ha!

 

[delray]

before I say anything I should be asking you if you can run a lathe or know of someone that can? you did mention something about a lathe earlier. that could be a big plus for what you also mention earlier going to the next lever. assuming you want this engine to go(good power).
if you do decide to use the stock cam and cut the extra material off the snowblower cam. the correct amount material you want left over would be .590 plus or minus a .001 or so. each cam may measure just little different and don't forget to chamfer the end just little.

this way you will know it will be the correct length and won't pop out the plug.
now if you really want to get fancy you could take advance of the newer compression release cam that comes in the ohh blocks and some late model flatheads. this came will allow you to advance the motor little and also able to pull the engine over without ripping your hand off.

there is one small drawback when going down this path. you will have to do little aluminum welding and machine work where the thurst washer rides up against the side cover.
as dave mention earlier you can use the dyno retainers and keepers and will have to machine the retainers just little so the single fat spring will clear the retainer correct. if you do go with either cam you will only need the 16 pound animal springs for the stock lift cam(.200 lift max) if you have gone down the path this far you also might want to clean up the bowls little and a 3 angle valve job wouldn't hurt either,but a lap job will work still. build your self a good intake. don't try to use the stock intake at all. way to restrictive. it would take a lot of rework to make a rupp style intake flow good. get your self a good header. a real header, not something you made up from the hardware store either. run a clone/mikuni 22mm carb.
and yes if you do have a bearing cover for it? install it for sure. one less thing for the engine to drag it self down. every little thing will help make the 4hp feel like a little animal. even with the stock cam the engine will pull easy up 4700+ rpm's all day.

 

[cfh]

Del i've done this cam cut mod on a bunch of snowblower motors and you're right, the measurement is pretty "loosey goosey" for the end of the cam. It's all over the place. I settled on .600" as the length average, from what i've measured. Because round numbers are easy for me to remember, and Tecumseh generally used round numbers (from what i've seen). If you pull the piston and put the cam and side cover in, you'll see there's a ton of play in there. they just didn't consider that a needy measurement i guess.

If you look at the end of the cam, you can clearly see the bandsaw marks. they didn't cut the cam ends on a lathe. Using a bandsaw gave pretty variable lengths. And yes as you said, the end is chamfered... Just mimic the old chamfering after you make the cut.

As for using modified cams, again i'm not a fan of this. But i'm not an "rpm guy". I like lower end punch, opposed to high end twirl. And i like my shoulder (a lot!), so modified cams aren't for me. Others dig this, but it just seems like deep and dangerous waters, on an engine that's 40 years old. My opinion is if you want that high end twirl, get a $100 predator motor and go to town. They don't make Tecumsehs any more, so i like to keep it under 4000 rpm (usually way under). Hopefully the old Tecumseh will last another 40 years. I *do* like DaveH's statement about the Arc rod though. That's a good plan and nice insurance....

 

[markus]

I'm sure the reason the OP wants to cut the camshaft snout off is because he has the good pre 1970 MCR camshaft to work with like seen below on the right:

IMG_37071

• markus
• Sep 16, 2012

Dave (OP) If the lobes look good and the lifters show that they were rotating through the years and not wiping out the lobe I'd give it a trim, I always liked the way those cams run. After reading your post yesterday, I was digging in parts bins to get everything together for another upcoming HS build and I spotted the last MCR cam I have. I grabbed it and compared to a later BCR cam to make sure that all other aspects of the cam (casting of the shaft), other than the big intake lobe and release mech came out the same as the the later BCR and it shows identical so there should be no clearance issues with a billet rod install over anything that would maybe have to be done with a later MCR camshaft.....I have never used and ARC rod, only tried some old style HS specific ones made in the way-way back.

I would say the freeze plug install would be pretty permanent so you would not have to think of it as a temporary measure. So if your journal bores are clean and in spec, gasket surface is good, and the oil fill hole/s have a clean smooth surface for the gasket to seal (ran into that issue a time or 2!) it would be worth doing to the cover. I measured the depth to wall in a non PTO cam sidecover last night as well and show an overall @ .8" from shoulder to the wall (inside the engine), Not sure if there is any depth change in the bore when they machined out the hole on those for the PTO and seal, if they bored in farther for the seal That would determine where you want to cut that cam, or set the depth of the plug, so you have enough clearance for the camshaft to float between the shoulders.

Are you wanting to actually modify for a lot more power, or are you just trying to optimize a stock appearing engine?