H50 New vs Old Piston opinion ...

Sixpac440

Sixpac440

#1
#1
I bought a rebuild kit for my H50 .. it included a new piston, wristpin and rings ...

Took the motor apart and the crosshatching looks great ... the old piston looks good too ...

The 2 pistons are a bit different ...

The new one is .388 shorter and weighs 7 grams less ....

The old one has a longer skirt and I think that would make it less wobbly ....

Both pistons measure the same O.D. ....

Question is .... Is there any reason I should use the new piston?
Beekeeper thinks I should re-ring the old one and use it ...

 
Sixpac440

Sixpac440

#4
#4
creia said:
WHY are you putting in a new piston/ring set?
Michael
Click to expand...
The motor is 46 years old .... mini bikes are not know for regular maintenance ... it gets regular use in the summer time ... I bought the kit before teardown.
I see wear on the rings is enough to warrant a ring change .... question is are new pistons any better than old ones, did a design flaw get re-engineered? a 1/4 OZ weight difference dosent seem enough to make a signifigant difference as capguncowboy stated.
If no one has a good reason to go new then the old one is going back in the bore.

My wife has an identical mini, maybe she could use it .. IDK.
 
creia

creia

#5
#5
I asked because putting in a new piston/ring set may not accomplish anything other than lighten your wallet. In fact, it may even DECREASE performance. (Now I know that I have your attention! LOL) You need to check the cylinder bore for excessive wear, taper, or out-of-round (It may have all of them). Remember, installing new rings will do NOTHING to correct those conditions. This is properly done with a T-bore gauge and a caliper or micrometer at numerous locations and compare it to a new cylinder bore dimensions or known service limits/tolerances which you can find in the Tecumseh repair manuals. If you do not have the desire, ability or tools to do this a good local machine shop that is well experienced in small engines is your new best friend. If your bore and rings are not EXCESSIVELY worn your existing rings have already "set" to the shape of the cylinder wall and will seal better than brand new (perfectly round) rings to the shape of the cylinder.
What is the compression of the engine with the existing piston/ring set?
Did the engine smoke and/or oil foul the spark plug?
What was the overall performance like?
Michael
 
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Sixpac440

Sixpac440

#6
#6
creia:

Mostly just looking to avoid breakdowns and holding up the crowd.

The crosshatching looks great all up and down the bore and there is no ridge at the top so I was gonna give it a pass ...
But I am here at work and I am a tool & die maker I thought your right ... lets check it ... I just checked the top and bottom in several places with my calipers (my bore gages are at home) and it checks 2.630 up, down and all around (that I could check).

When I put the rings in the bore I could see a larger gap in the old rings tho I did not haul out the feeler guages.

I also took .010 off the head while it was here.

If it runs as good as it did I will be happy!
 
creia

creia

#7
#7
OK- good information!
Seeing visible cross hatching is a good thing and your measurements of the bore sound very good. As far as ring end gap goes you would want to be in the range of .010"-.020". My son and I really like the H50 engine- they are REAL torquey. His last build was a Sears Roper that had an H50 that we swapped out an H60 crank and rod, a (mild) performance cam and heavier valves. Finally, combine that with a 2-speed jackshaft hat bike could really climb hills and it would get there VERY quickly!
Michael
 
OND

OND

#8
#8
Sixpac440 said:
I bought a rebuild kit for my H50 .. it included a new piston, wristpin and rings ...

Took the motor apart and the crosshatching looks great ... the old piston looks good too ...

The 2 pistons are a bit different ...

The new one is .388 shorter and weighs 7 grams less ....

The old one has a longer skirt and I think that would make it less wobbly ....

Both pistons measure the same O.D. ....

Question is .... Is there any reason I should use the new piston?
Beekeeper thinks I should re-ring the old one and use it ...

Click to expand...
I'm with beekeeper, I like the older piston with the longer skirt...and the top ring groove looks closer to the top of the piston....maybe a little more compression., just my two cents.

Are the wrist pins at the same height, from the top down ?
 
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creia

creia

#9
#9
The bore measurement you provided and the visible cross hatching tells us that the engine has never been rebored. For a 46 year old engine in that condition it indicates that it did not have that much use and was maintained very well- which is quite rare!
Michael
 
125ccCrazy

125ccCrazy

Well-Known Member
#10
#10
the longer notched skirts were mostly used in h60 due to the stroke for crankshaft clearance but were also used in H50...I'm not sure if they were a year change or used in specific applications in the h50... unless your trying to squeeze every little bit of power out of the engine for competition I don't think you would notice a difference between the two.. Unless the new piston is a genuine Tec part I'd use the original, the cheap aftermarket parts don't have the tolerance specs as the originals do..I ran into this with aftermarket valves in BB Tecs. the valves were quite a bit sloppier than an OEM tec valve..
 
Sixpac440

Sixpac440

#11
#11
Ring gap is .024 on the old rings and .012 on the new ones.

I have Chinese bore gages and Chinese calipers at home but they showed the bore to be straight up and down and round.

Top ring groove to top of the new piston is .1965 ... Old piston groove to top of piston is .182

Both pistons show about a .010 difference between the groove lands and the skirt with the skirt being bigger.

New = 2.611 / 2.620
Old= 2.6125 / 2.624
Clearly the old piston is a tighter fit.

Wristpin to piston top is .844 on both.

The old piston has more of a bevel on top and also has a "pusher"(?) ring behind the lower compression ring that the new rings and piston didn't come with.



Story I got with the mini is the original buyer loved this thing and has it until 2010 or so .. he had been in a mental hospital for years ... I'm the 3rd owner.
I paid $800 plus for it and drove over 500 miles round trip to get it but is was very original and came with a Michigan title.
Maybe it was too much but I really wanted that bike and to this day I have no regrets buying it.

I liked it so much that I started looking for one for the wife (she loves it) .. her's is also very original, we drove a bit over 300 miles round trip for that one.
 
Sixpac440

Sixpac440

#13
#13
creia said:
What BRAND/MODEL bikes are they? (Unless I missed it, I did not see you mention it anywhere in this thread?)
Michael
Click to expand...
oops ... yep, its me ...

Heathkit Hilltoppers .. one is a 1970 and the other I'm not sure ...
Here is a pic, mine is in the foreground, my wife is on her's right behind it and my brother and some friends are in the pic too ... we were out riding in Lowell Michigan ...



We ride alot in the summer ...
 
Sixpac440

Sixpac440

#14
#14
Went with the old piston and new rings ... got it back together and there must have been some gas in the float bowl because it started on the first pull!
 
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