H50-70 overall differences thread?

[markus]

Got a couple of mystery medium frame engines that I am going through-Incomplete/no tags. I got as far as figuring out they are both 70's style, both ball bearing sidecover, both aluminum block, and got the bore and strokes measured to see that one is an H50 and one is an H60. It looks as if the block were the same between the 2 but I don't have them fully apart yet.

I know the H70 will be a larger bore and I think they had some meat added to the exhaust fins as well which can be a tell usually but it seems the block style overall dimensions still kept the same (If I am seeing things right the side covers are a match still) and of course crankshaft and rod difference in all three, how about cams/valves etc.?

Anyway is there maybe a good read thread on differences or anything like that anyone can remember or has earmarked. Dunno if its just me, but the specific search engine this site uses will reject 3 letter words and phrases so you don't get very far tying to search H50 H60 H70 :laugh:

I've only done one H50, don't particularly care for them as I feel they are bit bulky but they are here an wanna see if I can do something with them and what a good combo to use is. For instance going H60 internally, I do have that block apart and the crank is clean and measures usable across the journals etc., but I dunno if that longer stroke was a disadvantage or a bonus :shrug:

 

[FirePowerMinis]

If the linked service manual is right, a 70 could be 246-281-305cc? Egad

 

[125ccCrazy]

Marcus,

the only real difference between the h50 and h60 are the cranks and rods... either combo will switch out with the other..h50 crank and rod into an h60 and vice versa... Physically an h70 crank and rod will fit an h60 or h50 and vice versa if you can find the right oil seal for the flywheel side to accommodate difference in crank bearing journal and block opening i.d and o.d... Externally everything from any of the three will fit the other including side cover... The h70 has a larger bore and larger intake valve, longer stroke and shorter rod..h70 has a larger rod journal also.

 

[Dr. Shop Teacher]

Mark-- I'll be interested to see what you think when you're done with them. I've got a '69 H60 that I'm starting on in a bit. After my experience with the H60 on the trail bike, I'm just totally impressed with the torque and smooth revving. My HS50 on the Wilderness is no comparison (both are stock). This "new" H60 I'm doing is probably destined for the Wilderness (a 6" wheel 525).

 

[markus]

Thanks for all the info guys :thumbsup: Randi, is the longer rod a weak link if I went the H60 route? If I was to build something to use I'd like to go ungoverned/custom carbed but not much more...just nice rider type engine.

 

[Dr. Shop Teacher]

Just thought of something...Piston Ring Gap. When I tore down the first H60, gaps were way out of spec. Second H60, same thing. I was able to source NOS 0.010 rings for the first build and I hope I've found them for the second build (will let you know if vendor comes through). That's a downside to these engines as the rings are hard to find.

 

[markus]

Just thought of something...Piston Ring Gap. When I tore down the first H60, gaps were way out of spec. Second H60, same thing. I was able to source NOS 0.010 rings for the first build and I hope I've found them for the second build (will let you know if vendor comes through). That's a downside to these engines as the rings are hard to find.

thats a pretty common theme throughout the Tecumseh line actually.

 

[Dr. Shop Teacher]

thats a pretty common theme throughout the Tecumseh line actually.

I hadn't seen it until these builds--the gaps are huge--something in the order of 0.040--with a true cylinder bore. The HS40 and the H35s I've done were good (and two of them had been rode hard). I've got an HS40 I've yet to crack open.

 

[125ccCrazy]

Thanks for all the info guys :thumbsup: Randi, is the longer rod a weak link if I went the H60 route? If I was to build something to use I'd like to go ungoverned/custom carbed but not much more...just nice rider type engine.

The h60 will be a shorter rod and longer stroke on the crank..H50 has the longer rod... I wouldn't say either will be any weaker than the other as long as clearances are in spec and the rods are in good shape... I have never ran a Governor on any engine for 40 years and only had one rod let go and it was on an hs30 in the 70's but the rod was sloppy on the crank already..back then as a kid the only fix I had was sand the rod cap down on a sand stone slab to tighten the clearance...it worked for a while.... You will be fine with either engine.

Just thought of something...Piston Ring Gap. When I tore down the first H60, gaps were way out of spec. Second H60, same thing. I was able to source NOS 0.010 rings for the first build and I hope I've found them for the second build (will let you know if vendor comes through). That's a downside to these engines as the rings are hard to find.

a little pricey but... New Genuine Tecumseh Rings 33316 TB/195 | eBay

if you ever do an H70 and can't find Tec .010 rings you can use Briggs # 297816

 

[Dr. Shop Teacher]

The h60 will be a shorter rod and longer stroke on the crank..H50 has the longer rod... I wouldn't say either will be any weaker than the other as long as clearances are in spec and the rods are in good shape... I have never ran a Governor on any engine for 40 years and only had one rod let go and it was on an hs30 in the 70's but the rod was sloppy on the crank already..back then as a kid the only fix I had was sand the rod cap down on a sand stone slab to tighten the clearance...it worked for a while.... You will be fine with either engine.



a little pricey but... New Genuine Tecumseh Rings 33316 TB/195 | eBay

if you ever do an H70 and can't find Tec .010 rings you can use Briggs # 297816

Hmm. I didn't know there was another P/N. I used 34855 for 0.010 rings for H60. Thx for tip.

 

[markus]

Thanks 125, Maybe both these here are actually H50's then, one is complete and one was a longblock, I tore into the longblock like a kid opening a Christmas present not measuring the stroke with it together, yanked the rod and compared it to a late model Powersport billet H50 rod that here and its a hair longer and just made an ASS-umption that is was a 6 :biggrin: The piston is notched for crankshaft clearance. once I get some open space to ge the other one opened up hopefully I will get it all figured out, Probably just build one and sell off the other usable parts to help fund it so I got some studying to do to make sure Whats what so I don't misrepresent parts.

Thanks for the help :thumbsup: