to replace short rod, or buy a whole crank and use a spacer?

dannygraves · Post by **dannygraves** » May 19th, 2008, 9:45 am

what do you guys think? I have an '86 crank that needs a new rod, but the crank journals fit a little loose in the main bearing anyway. I was thinking about buying a NEW '88 or '89 crank ($200) and using the cometic spacer ($30) rather than getting a $100 rod kit and paying $100 to have it installed on the crank, when the crank itself is worn...

100hp honda · Post by **100hp honda** » May 19th, 2008, 10:13 am

teemtrubble has a cnc machine right? have him cut you a 5mm spacer and weld it to the cylinder....now your only using 1 gasket. then get the new crank for $200. thats what i would do anyways

aloha450x · Post by **aloha450x** » May 19th, 2008, 11:32 am

Ibont believe yycan buy a new short ro?d can ya?

100hp honda · Post by **100hp honda** » May 19th, 2008, 12:01 pm

i thought somebody said they had a source for the short rod...but regardless, the longer rod is the better way to go if you ask me

aloha450x · Post by **aloha450x** » May 19th, 2008, 12:17 pm

caouldnt tell on that. but the 5mm shorter rod should in theory spin up faster and have a little less vibration. so same power but just less time. am I correct danny?

dannygraves · Post by **dannygraves** » May 19th, 2008, 12:23 pm

the shorter rod gives more power burst (which the short rod motors are known for) longer rod is smoother power and more topend. With the longer rod, the theory is that the piston is at TDC and BDC longer, so the ports are open longer. I think my timing might be different with a longer rod though because the piston won't be at the same spot when the crank is at X degrees.
If my stock crank wasn't loose in the bearings, I'd definitly keep the short rod. But it looks like for about the same price I could have a brand new setup. I also wonder if that 5mm really makes that big of a difference. Also since the '86 jug has bigger ports, the longer rod might amplify its already bitchen power

I guess there is only 1 way to tell... why is my next paycheck so far away!?

Post by **AlisoBob** » May 19th, 2008, 12:55 pm

The longer the piston sits @TDC, the higher the cylinder pressure builds before it pushes the piston back down..

dannygraves · Post by **dannygraves** » May 19th, 2008, 1:04 pm

same concept as advanced timing?

Post by **AlisoBob** » May 19th, 2008, 1:09 pm

No, advanced timing builds C/P as the piston rises too, hopeing to recover the added "push" on the down stroke.

Leaving the timing alone ( or even retarding it slightly), but adding the longer rod, gets the benifit without the penalty.

dannygraves · Post by **dannygraves** » May 19th, 2008, 1:13 pm

ok
looks like I answered my own question before I ever asked it...long rod all the way!

Mad Dog · Post by **Mad Dog** » May 19th, 2008, 1:37 pm

New crank or not, I would have it checked for true and balanced.

Slow old Fart · Post by **Slow old Fart** » May 19th, 2008, 2:00 pm

I would get the long rod crank. it is heavier and the power will be more like a new one. I do not care for the short rod as well. The long rod have a longer pull and the power is broader but you give up torque.

The newer rod places less stress on the rod and will last longer because of less rod angle.

I made a spcer for a 85 and it worked perfect. I think some cpmpanies still make them, when you rebuild a crank you are taking a chance on more of a failure. Sometimes thecrank can develop small hairline cracks in the can you will not see from pushing the rod pin in and out and can come apart in a motor and jack it up bad.

I have one on the bench right now that I ran with slightly sloppy bearing fit and it wore the motor out way premature. New works better most of the time.

I used to rebuild the older cranks because they are lighter and reved better so they made more power but you can pay permanetly if you are not careful.

100hp honda · Post by **100hp honda** » May 19th, 2008, 2:13 pm

Slow old Fart wrote:I would get the long rod crank. it is heavier and the power will be more like a new one. I do not care for the short rod as well. The long rod have a longer pull and the power is broader but you give up torque.

The newer rod places less stress on the rod and will last longer because of less rod angle.

I made a spcer for a 85 and it worked perfect. I think some cpmpanies still make them, when you rebuild a crank you are taking a chance on more of a failure. Sometimes thecrank can develop small hairline cracks in the can tou will not see from pushing the rod in and out and can come apart in a motor and jack it up bad.

I have one on the bench right now that I ran with slightly sloppy bearing fit and it wore the motor out wat premature. New works better most of the time.

I used to rebuild the older cranks because they are lighter and reved better so they made more power but you can pay permanetly if you are not careful.

2 days ago your buying into some jackholes nonsense when he says R50 rusts the motor..........today your writing a 1000 word manifesto on how a crankshaft works ???

Post by **AlisoBob** » May 19th, 2008, 2:41 pm

100hp honda wrote:
2 days ago your buying into some jackholes nonsense when he says R50 rusts the motor..........today your writing a 1000 word manifesto on how a crankshaft works ???

nmdesertrider · Post by **nmdesertrider** » May 19th, 2008, 5:03 pm

I didn't have any problems getting a new rod for my 85, any OEM place should be able to get it.
Danny, don't mutt your engine up!

Slow old Fart · Post by **Slow old Fart** » May 19th, 2008, 6:24 pm

100hp honda wrote:
Slow old Fart wrote:I would get the long rod crank. it is heavier and the power will be more like a new one. I do not care for the short rod as well. The long rod have a longer pull and the power is broader but you give up torque.

The newer rod places less stress on the rod and will last longer because of less rod angle.

I made a spcer for a 85 and it worked perfect. I think some cpmpanies still make them, when you rebuild a crank you are taking a chance on more of a failure. Sometimes thecrank can develop small hairline cracks in the can tou will not see from pushing the rod in and out and can come apart in a motor and jack it up bad.

I have one on the bench right now that I ran with slightly sloppy bearing fit and it wore the motor out wat premature. New works better most of the time.

I used to rebuild the older cranks because they are lighter and reved better so they made more power but you can pay permanetly if you are not careful.
2 days ago your buying into some jackholes nonsense when he says R50 rusts the motor..........today your writing a 1000 word manifesto on how a crankshaft works ???

Some oils are Known for when you open the cases up the bottom end will be dry and if you let the bike sit for a while the crank and the mains go bad. Golden spectro had a rep for this or running the bike lean can do it to. You can have rust problems from letting a 2 stroke sit for a few months or more and some oils are better than others about kepping all the parts rust free when the bike sits.

Some people just don't know this stuff I guess.

britincali · Post by **britincali** » May 19th, 2008, 6:27 pm

Any part of the motor that comes in contact with air is suseptable to oxidation, I dont think it has anything to do with the oil used.

Slow old Fart · Post by **Slow old Fart** » May 19th, 2008, 6:31 pm

nmdesertrider wrote:I didn't have any problems getting a new rod for my 85, any OEM place should be able to get it.
Danny, don't mutt your engine up!

if you like the older style power the short rod is better. It definitely pulls out of the hole better but the power band is shorter. The spcer setup if done right works just as good as the new motor wirh the new style case. The guy who machined my spacer made it to where the contour followed the cases perfectly.

It is actually a more reliable setup.

nmdesertrider · Post by **nmdesertrider** » May 19th, 2008, 6:32 pm

I can believe it...not gonna happen in NM or CA but in places like NJ it will rust solid in no time flat.
Lubricants do have varying degrees of water displacement ability.

Slow old Fart · Post by **Slow old Fart** » May 19th, 2008, 6:35 pm

britincali wrote:Any part of the motor that comes in contact with air is suseptable to oxidation, I dont think it has anything to do with the oil used.

No but some oils coat the parts better in the betton end. I read 3 different threads where guys were saying when they took the motors apart they noticed rust with the r50 on the crank and mains when they let the bike sit.

A oil that burns off and does not coat will do this but the oils that burn can actually make more power and gum up less.

britincali · Post by **britincali** » May 19th, 2008, 6:45 pm

Slow old Fart wrote:
A oil that burns off and does not coat will do this but the oils that burn can actually make more power and gum up less.

What temp an oil burns at has absolutly nothing to do with the crank.

100hp honda · Post by **100hp honda** » May 19th, 2008, 7:05 pm

look, i cant speak for R50 or other oils but im sure they say something similiar to what klotz benol says: "not to be used as a storage lubricant". if your in 80% humidity and the bike sits for extended periods of time in a mouse infested barn, it may very well develop rust or corrosion, dry rot the seals, gum up the carb and many other things.....if this scenario happens, the bike owner should be hit in the face with a hammer and forced to sell his bike

britincali · Post by **britincali** » May 19th, 2008, 7:07 pm

100hp honda wrote: if your in 80% humidity and the bike sits for extended periods of time in a mouse infested barn, it may very well develop rust or corrosion, dry rot the seals, gum up the carb and many other things.....if this scenario happens, the bike owner should be hit in the face with a hammer and forced to sell his bike

Agreed 100%

It happens a lot in england, anything old and stored has rust everywhere and rotted seals.

Slow old Fart · Post by **Slow old Fart** » May 19th, 2008, 7:38 pm

Thats the thing how are you going to stop it in humidity,it was just a thread I saw on R50 when I punced it up.

Slow old Fart · Post by **Slow old Fart** » May 19th, 2008, 7:38 pm

britincali wrote:
Slow old Fart wrote:
A oil that burns off and does not coat will do this but the oils that burn can actually make more power and gum up less.

What temp an oil burns at has absolutly nothing to do with the crank.

good point.

BannedCR500Riders.com

to replace short rod, or buy a whole crank and use a spacer?

to replace short rod, or buy a whole crank and use a spacer?