Topic: Should I or shouldn't I...that is the question

[techy5025]

Ok..the resurrection of my new/old sandcast is mostly down to the
engine and the question is..........should I tear it down or not??

Keeping in mind that the value of the engine is in the sandcast cases and
that the engine was running before I tore the bike down is it work the
risk to disassemble it to inspect/replace gaskets, etc.  The bike had about
8K miles on it.

The alternative is to pull off the valve cover and oil pan, peek around for
obvious stuff, and thats it.  Or just pretty up the outside of the engine and
nothing else.

The sandcasts had a design problem that caused the primary chain to break
and destroy the cases.  If the fix was to replace the chain with a "stronger"
one or something else, it might pay to do the same before it breaks.  If the
cause for the breakage is something preventable (overreving maybe), then
I can probably prevent that.

I'm also not sure if Honda made an in-line fix at some serial number that solved
the problem and the worry goes away....or did they wait for the diecast cases
to fix it.

I plan to use this bike as a casual rider so it definitely won't be parked.

Thoughts are appreciated especially if someone knows about the chain fix.

Jim

[Magpie]

I always thought it was the drive chain that broke not the primary chains. All the welded cases I've seen (I have 2 sets now and a friend has another set) are welded at the primary sprocket area. I think there was even a "guard" there at one time. Honda didn't know the power available and had weak drive chains it seems.
What to do? You'll get tons of opinions of course - mine- compression check, check how much adjustment is left on the cam chain adjuster, pull the oil pan to see what is lurking there, look under the valve cover for issues there, if anything. If all looks good, polish the hell out of it, place it gently in the frame and go for a ride. As a caual rider it should see red line only several times per ride so all should we well.
My (jealous) opinion of course.
Cheers,
Cliff.

[cbjunkie]

dammit. somebody turn on the Hondaman searchlight...

[mwvachon]

I just checked the 'bible' (Honda 750, by Mark Haycock - don't own it? Get one! An SOHC must have!) and he says there were rumors of issues with the primary chain in the sand-cast models, but he could find no real cases/documentation of such. There were a number of issues with the final drive chain and sprockets however....

You could do like I did - just remove the head (left the jugs in place). This gives you a better starting point with a fresh head gasket and all new seals/gaskets in the cyl head.
JMHO

[MRieck]

 Final drive chains were the problem not primary chains. Big trick in the old days was to substitute CR primary chains for OEM primary chains.

[toycollector10]

If it's not broken, why fix it?. I only recommend that you replace the drive chain to the rear wheel with a top quality non O-ring chain (no clearance in the drive housing), change the plugs and maybe the points, make sure the plate is NOS as the later ones flex and affect timing), tune the carbs and adjust the valve clearances. Change the oil and filter and maybe the air cleaner and see how it runs. Get your carburettors tuned and if it goes ok why spend thousands of dollars on the gizzards....My understanding is that these engines are bulletproof and good for about 100,000 miles. Am waiting on HondaMan to post, he will know what to do...

[bryanj]

Problem was a small diameter front sprocket (16 tooth replaced with 17) with a badly routed battery breather letting acid onto the chain which weakened it.

[Lumbee]

...as far as the chain problem, I'd do a 530 conversion with new sprokets, and problem solved.  As far as the motor (if it were me) I'd "clean up" the top end, that is, get a full gasket set and replace all the top end stuff, from the base gasket up.  Clean up the valves (remove deposits) while your at it.  To me this is cheap insurance...nothing like getting everything back together and that leaky head gaskets shows up halfway through the riding season.

[GroovieGhoulie]

Problem was a small diameter front sprocket (16 tooth replaced with 17) with a badly routed battery breather letting acid onto the chain which weakened it.

Didn't that small front sprocket though, make for some wicked acceleration?

IIRC, the 16/45 original ratio is something like 2.8xx:1 versus the 2.6xx:1 of the 18/48, so that should make the earlier ones a bit peppier.

[byidesign]

Only 8k, wow if all checks out, leave it alone, it will outlive ya,
    with decent care, and the new superior oils, 8k is
      "just broke in"
              Enjoy it.....
                  Bruce