750 cylinder issue

hi,

on my 71 750ccm commando the two 5/16" threads are pulled. these were already helicoild by a previous bodger in a false angle. there is no space left for a insert nut. what an anger. i just investet in new pistons and honing. i found someone doing deposition welding and drilling new threads, but i am curious if it will work.

i consider to buy a new cylinder. Beeing a newbie to commandos, i dont know what to choose. Is the Maney Alu-Cylinder a good thing? are there any other alu-cylinders available? are through-bolts a problem? What do you suggest?

thanks in advance for your help!

Who's about a photo?

There are oversize 5/16-18 thread inserts available. My favorite is the Big-Sert from Timesert http://www.timesert.com/ . As long as there is enough metal left, you could remove the heicoils and use a mill or drill press to drill and tap the holes straight for the larger inserts.

Ken

lcrken said:

There are oversize 5/16-18 thread inserts available. My favorite is the Big-Sert from Timesert http://www.timesert.com/ . As long as there is enough metal left, you could remove the heicoils and use a mill or drill press to drill and tap the holes straight for the larger inserts.

Ken

Click to expand...

This ar nice little things! Thank you.

This is a photo of the probllem. Just about 1mm "meat" left. You can see the bore comming out in the pushrod tunnel not far under surface. The studs are bent, because the head didnt fit otherwise.

Well , now the Cylinder is already welded and i keep you informed how things going. I should have posted and asked here before.

What you do is what a friend has done for his customers with the same problem...you get the holes cleaned out, 'spray brazed' and then remachined back to standard. NOT cheap and a bit messy but I am told 'a damn sight cheaper than a new barrel'.
I shoved 'spray braze' into Google and information appeared....

FYI
The number 1 threaded hole there in the middle stripped one me once. It was a simple(very simple) matter of tapping it to 7/16-20 and using a socket headed cap screw from then on. I added 5ftlb's to that particular bolt to 35ftlb's total.

the cylinder is welded, new threads cut,. head gasket is oil thigt. compression ratio is 9.4 and the bike runs well. unfortunatly there seem to be some welding pores between 2nd and 3rd fin to the pushrod tunnel.
i tried to get the oil out of the pores with break cleaner and compressed air, used bearing adhesive and blow it in with compressed air. then i gave some drops of loctite 660 and made a kind of filling with solder, pin punch and hammer around the problem zone.
Well, this is oil thigt now, but i guess not very long.
now i think it was not a good idea to go this way (welding the cylinder). i intended to have a reliable bike.

Hi,

I know almost nothing about welding ally, but do you know if they used argon or helium as a shield as apparently helium is best for avoiding porosity in certain circumstances. Just curious after your situation but as I say I know little but would be interested if you know.

Jg

manual metal arc welding with some kind of nickel based elektrode, no gas involved.

i just wanted to post how things ended up with this approach.
both 5/16 threads were milled out and welded up from pushrod tunnels, new holes drilled and new threads cut. pores are comming out near the ground of one hole.

Your last resort would be to remove the studs and reinstall with a sealant such as loctite 515 or 518 in the stud holes taking care not to create a hydraulic lock as you torque the studs back in. That should work provided the oil is wicking down the stud threads and then exiting out the bottom of the stud hole.