RJ's 750 Bonnie engine overhaul by GP

[grandpaul]

Received this Bonnie engine just before Christmas and tore it down to inspect and prep for overhaul.

RJ had already had the head & barrels done by someone else, and included a new set of pistons & rings to go on the overhauled botom end. Carbs are in the box for overhaul as well...

Starting point looks "decent" enough from the outside...

Primary cover came off first, hmmm, looks like some metallic particles in there...

Everything else in the primary APPEARED to be in good shape-

 

[grandpaul]

Oops! That nice new Wassell stator looks like it's been rubbing the rotor for a while-

Yep, there's the evidence of some serious heat soak on the rotor-

Otherwise, not too bad-

 

[grandpaul]

Although the primary chain was loose, and the adjuster was all the way in, the adjuster blade is brand new. Oil transfer holes were clear-

Alternator rotor, engine sprocket & clutch hub slid right off without a fuss using my Posi-Torque puller (everyone needs a set in 3" & 4"). Drive sprocket looks okay-

Over to the timing side, everything looked decent on removal of the outer covers (I took pix of the timing gear markings for the record, but the marks were not lined up, so they're just for reference)-

 

[grandpaul]

Since I'm trying to involve four different forums in this project, I'm going to do the rest of it via update links instead of posting and editing in 3 different formats every time I do an update.

Here's the main build thread on my Delphi forum-

Bonnie engine overhaul

 

[CarlS]

Thanks, GP. The cases look really good. I see you found the source of the metal particles. I will be following this rebuild.

 

[grandpaul]

RJ informed me that the engine previously experienced a holed & trashed piston, hence the start of the overhaul.

He had no clue the rod bearings were rapidly giving up thier stuff. I would have expected a pretty noticeable rod knock with that much wear, although it may have been the onset of catastrophic failure, and I'm wondering with the inside of the oil pump is going to look like...

 

[CarlS]

With the onset of a catastrophic failure like that, I would suspect the oil pump is failing.

 

[Rocky]

Having torn into the bowels of both the engines of my vintage bikes I always find this stuff very interesting. Good going GP :y115:

 

[grandpaul]

New parts arrived just before the weekend-

 

[CarlS]

That brings back memories! Very cool.