Swapping con rods | GTAMotorcycle.com

Swapping con rods

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timtune

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I'm playing mix and match with 2 old SOHC 750 honda motors. I want to swap con rods from one to the other (one set has bronze bushings on the small end and one is mangled).
Can I simply swap them over, check the gap with Plastigage and be done? (assuming good gap). I guessing I'm wondering (overcomplicating?) if they needed to seated or "bed" in in any fashion.

Thanks
 
I would be making sure they carved the same and weight is the same
 
Pistons should be easy. Take the 8 I have and find the best four. Carve? No reason to replace them (but have yet to check ring gap)
 
If the rod fits, you can use it.
... but if you're holding the rod in your hand WHY are you not installing new bushes.
Have you MEASURED the bush to find that after 40 odd years they're not round anymore?
And you don't re-use pistons by "Take the 8 I have and find the best four."

It doesn't sound like you're doing this motor any favours.
 
It's very strange. I can't find these bronze bushings in any of the other 3 or 4 SOHC motors I have. The SOHC forum guys are confused by it.

Actually I DO re use pistons this way. Why would anyone not use the best ones?

FWIW years ago I built a whole motor with the mix and match method and it plugged away (hell let's be honest I beat on it hard) for many years just fine. Keep in mind this is a motor designed over 50 years ago. I don't believe the tolerances are as tight as something newer nor is it likely to be as highly stressed so it's not as "finicky" if things arn't good to the fourth decimal.
 
I've pulled engines apart where the small end had been bored out and a bush pressed in to repair damage. They could also be aftermarket. Rods that come from the manufacturer like this will have the bushing made from premium-grade bronze alloy so not just a standard bronze bushing.

As Bitzz said you probably want to measure.
 
timtune said:
Actually I DO re use pistons this way. Why would anyone not use the best ones?
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IF you were to re-use the 45 year old pistons (I wouldn't even consider doing that) the BEST piston is the one you took out of each hole. Used pistons ONLY go back into the hole they came out of.
Mixing and matching used internal engine parts is NOT a good idea.
 
You and I do things differently bitzz. My past experience has shown that used pistons WORK FINE in this engine (assuming proper ring gap etc). And based on that experience I'll be doing it again.
I also never replace crush washers. To each their own.
 
timtune said:
I'm playing mix and match with 2 old SOHC 750 honda motors. I want to swap con rods from one to the other (one set has bronze bushings on the small end and one is mangled).
Can I simply swap them over, check the gap with Plastigage and be done? (assuming good gap). I guessing I'm wondering (overcomplicating?) if they needed to seated or "bed" in in any fashion.

Thanks
Click to expand...
I prefer re bushing the originals. Honda’s are tough and well designed, if the old rods and crank are good, keep them matched to the original motor with new bushings.
 
Bushings are the problem. Nobody seems to think they ever came witha small end bushing. I have about 5 motors. Only this one has them.
 
timtune said:
Bushings are the problem. Nobody seems to think they ever came witha small end bushing. I have about 5 motors. Only this one has them.
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Did they come with bushings or has someone opened them up and added bushings at some point? Doesn't help you with your problem, I was just interested.
 
bitzz said:
Did you know there is eight different con rods offered in SOHC Honda 750's?
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I did not even though I have a bunch of them.

Which ones have the bushings?

FWIW the swap in question is between 2 1978 F's (same motor same year)
 
GreyGhost said:
Did they come with bushings or has someone opened them up and added bushings at some point? Doesn't help you with your problem, I was just interested.
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No idea. Hoping bitzz will shed some light here.
 
Thanks Bitzz. I'm not likely going to dig any deeper. If they fit and work they're going in.
 
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