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Another rescue project '74 75/6

'Cuz I'm curious, what is a new head worth? I have, Ahem, fudged things like back together (Back to serviceable) but that does look like a really deep one.
OM
 
One of those..."If ya have to ask":hungover
Saw a new one for $800-ish...looking at a few used on the Net, but none as clean as this burnt one. I had planned on having the heads re worked for the valve seats at some point...just not this soon. It is pretty deep....looks like a factory casting groove as it's so smooth.

The sleeve in the head acted like a chimney...really got hot!

And the stud is destroyed...somehow it tightened when I checked it the first time
 

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DANGIT...:banghead

Pulled the heads to do a complete top end seal since I lost the head gasket on the left a week or so ago. Found a bit of an issue as I noticed a sign of major heat scarring on the intake rocker and the bottom nut was loose. A little sink in my mood of just replacing the gasket.

I had checked torque when I was going thru the bike when we first got it and recalled that same head bolt was the one not near torque value.Yet it tightened back to spec. I was closing in on another oil change and valve check. The bike has been running well and no signs of a leak or popping until it let go.
I had found most of the service history and never saw a head re-torque in it's 20K previous life. Maybe it was just waiting on me.:violin

The threads are shot on that stud and must have been working itself loose again. End result is a damaged head. Good news was the valves and piston dome are clean from any carbon build up and I think the gasket mating surface on the left cylinder isn't damaged. Now have two 750's on the lifts waiting on parts and patience.
Hey Steve, that picture shows what a recessed valve looks like. I'm pretty sure that your exhaust valve there is sunk way down into the seat. It's a good thing you took that cylinder apart when you did.
 
Nice old relic. I have a 75 R75/6 I bought new, that has over 175,000 miles on it, out of the 20 motorcycles I have bought or still own, it has been the best one of the bunch.

I put dual disc on it early on as it did need better brakes. It got a top end and a clutch at 90,000, when the gearbox was out it got the updated shifter assy. I've had to repair the drive splines on the final drive.

Not bad for 38 years. I hope you have fun with yours.
 
"debris field of carbon,dirt,and rust that spewed out of the mufflers...mostly on the floor...a LOT on her bike Luckily for me she was not there to see that happen."


Funny, same thing just happened to me, my son keeps his newly restored MGB in my shop, I was able to blow all the carbon off before he saw it..
 
bump

Was needing an Airhead fix and just getting time to get back to work on the '74. Have not had the heads repaired/replaced yet.
Have had the /5 on a lift going thru it, front end off about midway thru overhaul when I had a duh moment.:doh
The PO had installed a Siedenbrock kit on this bike and my thoughts were to move it over to the /6 and leave the 5 a 750. There was a deep sump from the 5 all cleaned and ready as well.

Had lifts side by side and swapped the top ends. I had the new cylinder stud and pushrod.seals sitting here since October. No issues with the swap, and one bike running another further along in teardown...win-win.

Took it out for a couple of runs yesterday ,and again today after one more head torquing session. Running pretty well and can feel the additional displacement for sure.
I did experience a throttle roll-off compression braking effect I don't recall the 750 doing. 4th gear at 60ish and bucks upon complete roll-off, also 5th around 70. Sure feels like downshifting one gear to many without the tire skidding. Normal side effect for the larger bore on this bike?
 
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