Engine rebuild after a broken rod?

[jjwithers]

Wow! Been a while since i have been on this forum. It's all new and fancy!
Hello to Duane and the regular crew! Your advice over the years has lead to my success of getting my 2 bikes roadworthy again.

I'm considering buying a basket case bike to build another cafe bike. I found a potential bike (long distance) and the R75/5 engine has a broken rod...
I'm wondering if this damage the crank or the case in any way? I am planning on replacing the pistons/jugs, having the heads rebuilt, doing a complete engine tear town to replace the crank bearings and seals, etc...
but i've never dealt with this kind of damage before and i am concerned about it being too bad of a donor to start with. Or, since i will be that deep in the engine anyway, simply replace the rods along with everything else, and resurrect this old gal.

Any advice would be appreciated.

-Josh

[Deleted User 287]

I broke a connecting rod on my original '79 R65 engine. I didn't know enough to stop the engine when I felt the left side loose power, and the bottom half of the rod punched a hole in the top of the crankcase, broke the camshaft in two and took bits out of both cylinder and piston skirts. A real mess.

[vanzen]

A connecting rod that comes apart can do all manner of damage – or not.
One can only guess as to the extent until the pieces are in hand, inspected, and measured.

IMO, the question to consider will be
if the price accurately reflects the mc's value without an engine.
With that strategy,
and given that the thought of rebuilding or replacing the engine is not problematic –
anything in the engine-case that will be salvageable is a "bonus".
Otherwise, it's a crap-shoot.

[mattcfish]

It depends how the rod broke. No matter though, /5, /6 blocks (even ones with good bottom ends) are pretty cheap on eBay etc. Less than $150. http://cgi.ebay.com/ebaymotors/ws/eBayI ... MEWAX%3AIT
/6 blocks are tougher than /5 around the front bearing. Late 70's-90's blocks have a better oil path.

[jjwithers]

Thanks guys. Part of the allure of this bike is that the numbers match, and it is cheap.
Provided the case isn't damaged...
worst case...
I know a new crankshaft (if needed) is $800. And the rods are about $250 each.
That doubles the cost of the bike.
Then add all the bearings, seals, pistons, cylinders, etc... and the bike's cost is tripled, etc...

so again, it sounds like - if the case is OK, at least i have a solid foundation to bring another bike back to life. if there is any case damage, i might as well wait for a better donor with a better bottom end.

I'll call the seller today and try to get the straight story.

-josh