I've just been reading about that kind of upgrade (gentleman's express) I would get the same satisfaction from bringing this engine back to stock form. That would be a LOT less costly wouldn't it? I don't know what rebuilding an engine really costs, never had to, but i'd like to be able to say I saved one from the scrap pile instead of parting it out.
Where do I start? Hone the bad cylinder so it can be measured? I've repaired valves and head gaskets, but never a whole engine before.
That motor is really toasted. It will cost you a lot of money to restore it to proper working order: pistons/rings, overbore, very likely all new crank bearings and rod bearings, the head will need immense work too. All this work and these parts are expensive and not DIY. Assembly labor is about the only thing you can perform yourself for a savings. But you will also need decent measurement tools and quality torque wrenches.
I'd expect a motor that neglected will also show signs of oiling problems in the head, on the cam, the cam journals and rockers. Then you need to assess the valves and guides.
I'm not a fan of 605 kits. It thins the cylinder liners for little to no power outcome. You can achieve a VERY healthy motor with 59mmm pistons (Wisecos), a hearty cam (126-00 or 126-20) and send the head off to Mike Rieck. A stage 3 workout from him will yield far more usable, reliable power than a 650 cam and 605 pistons.
At the end of it, you'll have over $5k tied up in parts and labor before assembly, make about 55HP, and have a bike worth little more than that. Know this going in and expect to fully lose all the capital in a resale transaction later. Point is: you can not recover money invested rebuilding a motor this trashed, no matter what the project end goal is. But you can and will enjoy the dog piss out of it, learn heaps, and have a fun bike to ride that you built. For whatever that is worth to you.
There's the voice of reason I was looking for. I have two 550 and three 750 motors in various states of health that I hope to put back on the road someday. It all started with my first 750 parts bike that had a stuck motor. I took the head off, found the rust ring at the top of cylinder 3 and said "someday, I'm going to fix this". So I broke a ring putting it back together, wrapped it up in oily towels and plastic sheeting and thought, " I need to learn a bunch before tackling that"! So this motor is all about that learning process, it's easier to proceed when you're not worried about making a mistake. Last night I was trying to asses to condition of the cam and had trouble finding the info I needed as well as my plastigage wasn't big enough to measure the clearance that's there! The cam journals have visible grooves you can feel with a fingertip. My father-in-law made sure I was prepared to measure stuff ( surface plate, height gages, precision gage blocks, v-blocks, calipers and micrometers up the wazoo), I just need to get comfortable with measuring things accurately.
I'm sure calj is right, this motor isn't worth the expense of parts, but will go a long way in getting me ready for the one that is worth it. First purchase will be a cylinder hone so I can practice measuring the results. I'm open to suggestions for that purchase.
Since there is no clutch basket, I was able to spin the gearset with my fingers and study the shifting action closely. I FINALLY understand that jumble of parts that make the shift drum move one step at a time. The dogs and shift forks look real good too, but we shall see. Time to go read the hondaman book again (and again) , oh, and clean the shop!
Thanks, and now back to our regularly scheduled adventure...
