Topic: Parts Interchanges

[JLeather]

I'm attempting to assemble a very nice 836 motor this spring for my bike and I have some questions about interchangeability.  I have a whole pile of junk-motors to nab pieces from.  Notables include a mostly complete '74, a '72 that was a runner til it lost compression, 2 locked up '78F motors, and some parts.  I believe I've heard that some oil-passages and stuff changed causing certain year cylinders/heads to no lnger cross-over.  Anyone care to enlighten me on that?

The '72 bottom end was a good runner til last year (it was in my chop) and is my most likely candidate for the build HOWEVER my bike is getting a 180x18" rear tire.  I think the later bottom ends leave me a bit more clearance for such a beast right?  Can I rebuild a '78F bottom end with 71-76K top ends?  I've got a set of cylinders already bored that I think are for a '72 and I've got a ported head (very nice) from a '74ish.  What kind of problems am I likely to end up hitting?

[JLeather]

Oh, yeah, and on another note what about the bearings (rod, main, and tranny)?  The 72 ran, and didn't knock or anything, but if I'm putting a nice top-end on it how do I make sure the bearings are ok so I don't end up pulling it out again next year?  Is there a way to check the bearings out without splitting cases?  Also, aren't the stock rod bolts non-reusable?  If I have to open the rods up to check bearings aren't I further ahead to just replace them and be done with it?  No idea how many miles the bike has cause there was no speedo when I got it (in fact there still isn't).

[City Boy]

Jleather,there is no real way to check plain bearings without splitting cases,inspecting,and plasti-gauging.Oil pressure check will give some indication though.Steady pressure with no wavering is a good sign.OEM rod bolts and nuts are reusable.If money no object,change bearings and be done with it.Send me old bearings!!!   Rock On

[City Boy]

P.S.Send rod bolts too!!   Rock On

[JLeather]

Man, money is ALWAYS an object.  If I can check these bearings and they're good, they're stayin put.  So I can take the rods off and plastigauge them, and then put them back on with the stock rod bolts?  It's not gonna be a race engine, it's going in a chopper.

[junkyardjon]

yup, thats what he's saying.
JLeather i seen you on someother forums i think no? LOL

[paulages]

Man, money is ALWAYS an object.  If I can check these bearings and they're good, they're stayin put.  So I can take the rods off and plastigauge them, and then put them back on with the stock rod bolts?  It's not gonna be a race engine, it's going in a chopper.

i believe they're good for 3-4 torques. if you're pretty sure the engine's never been apart, i'd say you'll be fine reusing them.

[scondon]

  I really like the 78F bottom ends cause they usually have low miles on them and have a bit stronger rod bolt. Also Honda's manufacturing process had gotten pretty good at that point and parts are well balanced(just my opinion). Swap the cylinders and head from a 74-76 onto that bottom end and use whatever cam towers that look best.

[JLeather]

Do the oil passages line up between a '72 head, '74 jugs, and '78F bottom end?

[scondon]

  Yes, they do. The F2 head and cylinders are modified to return on only 4 of the 8 passages but the F2 bottom end collects the oil the same as other years. Switch the cylinder AND head with a earlier engine and you'll be just fine.

   Any SOHC 750 head will match up with any SOHC 750 cylinders( the F2 being the exception ) and bottom end. Don't know for sure about the 69-70 run but 72-78 should have no trouble with oil returns matching up.