Tri Z crankshaft usable or no???

[1972mercury]

I bought a tri Z this last summer with a locked up engine tore the motor apart and found out mice got inside the engine and seized the crankshaft then pulled the engine the rest of the way apart to look at the crankshaft better it dont look to bad. I cleaned it up pretty good it is gonna need a new rod and rod bearing but from the pictures what do you guys think usable or not???

[barnett468]

Hello

Absolutely useable for trail riding etc. needs new crank pin with rod and bearing. Just wire wheel/sand it good, remove any lumps.

[250rRoostmaster]

That pitting is pretty ugly, you need to check the run-out on the crank to see if it's still in spec. Hondas are something like .002". If its over that on the run out its no good. I would replace for piece of mind since you already have the cases split but that's just me. The pitting might have affected it's balacing as well. i would have it checked out at the very minimum. Hope this helps

[barnett468]

Hello 72Mercury


250Roostmaster has brought up some good points and concerns fortunately for you they don't apply in your particular case.


In your particular case you do not need to be concerned about any amount of existing run-out since you are rebuilding the crank and any amount of missing crank material causing imbalance and subsequently increased engine vibration, it simply can’t happen. Your single cylinder engine vibrates anyway simply by design so the only thing removing small to moderates amounts of material from the crank will do is just change the rpm at which the engine vibrates by an imperceptible amount.

Yes it would be nice to have a nice looking non pitted crank but it’s a Tri Zinger, not Marty Smith’s RC125.

ENGINE BALANCE – Most people don’t truly understand engine balancing. With regards to a motorcycle engine they are not balanced in the true sense of the word. This is especially evident in single cylinder and offset pin twin cylinder engines as is the case with the Harley Davidson motors. If they were truly “balanced” then the ATC 250R and Kawi KLT motors would need a counterbalancer to reduce vibration to an acceptable level.

CRANKSHAFT RUN-OUT – Another item often misunderstood. All crank pin type engines/motors have run-out to some degree. The closest I personally have ever got one to 0 is .00025”. That’s ¼ of 1 thousands of an inch. Run-out of any amount can easily be corrected during crank rebuild providing the crank shafts are not bent [never seen one] or the crank pin holes are worn [only seen 1].


MOTORCYCLE ENGINE BALANCE ARTICLE

http://www.dansmc.com/counterbalancers.htm


PS - Do you own a 72 Mercury? I had a 69 Mercury Montego 351 4v Cleveland, cool car.

Hope this info helps.

[barnett468]

Typo correction

"motors would NOT need a counterbalancer."

I have no edit button

[1972mercury]

Typo correction

"motors would NOT need a counterbalancer."

I have no edit button

Well that's good to know I really don't got the money right now to go buy another crank oh and the 1972 mercury wasn't a car I had it was a mercury snowmobile I had a couple years ago neat looking sled!!!

[Dirtcrasher]

It appears as if it was a submarine for awhile. As long as the big end bearing and shaft are tight, use it.

However it does look like it was sitting in some water and you could do allot of other mods just to see it blow up.

Check the crank, ZERO movement up or down as well as sideplay and make your decision from there.

[barnett468]

Hello 72Mercury

Glad I got the correction in there, lol. Yeah the Mercury snowmobile is cool too!