exhaust manifold bolt hole stripped

My '75 Z1 900 has an exhaust stud hole stripped. Has anyone used a Helicoil Kit to repair this? I’ve used them on larger projects before and they worked well. What I’m worried about is....1- looks as if someone did some grinding around it so there is material missing thus a thinner wall. And 2 - this stud is a fine thread and Helicoil only offers a coarse thread for a M6 size. Should I just go with the coarse repair kit and replace the stud to match? Perhaps someone knows of different kit or way to repair it?

Carl

The later engines changed to a 8mm stud, you might be able to re-tap the holes and then use the 8mm studs. You'll need the holes drilled out in the exhaust clamps and larger nuts to tighten them.
Make sure the tap used is a "bottoming tap" as the other(plug) can have a sharp point that may pierce an oil gallery in the engine.

I'd check with www.z1enterprises.com for the studs & nuts.

They sell Stepped studs, so you retain the 6mm at the exposed end, and 8mm where it will go into the head. Such as this,$2 Item, although it doesn't state length on that site, this is a reference anyway. Napa should have them, I believe, or a good machine shop.
www.034motorsport.com/hardware-fittings-...mm-to-6mm-p-231.html

Hand tap information:

Chamfers for Thread Cutting Taps ( taper, plug, bottoming ) The tap chamfer is the tapering of the threads to distribute cutting action over several teeth. The type of hole to be tapped has much to do with the chamfer style of that tap that's best suited. Some holes go all the way through; some, while not through-holes, are relatively deep; some are quite shallow (a little deeper than diameter). Each of these three kinds of holes - through, deep-bottoming blind, and shallow bottoming - has a tap chamfer best suited to threading requirements.

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Taper Taps - This style, with a 8-10 thread chamfer, has the longest chamfer of the three to distribute action over the maximum number of teeth; and the taper also acts as a guide in starting the cutting action in the hole. Taper style taps start the thread square with the workpiece. Taper taps are commonly used in through holes and in materials where a tapered guide is necessary.

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Plug Taps ( Seconding Tap)- This style, with a 4-6 thread chamfer, is most widely used in through holes and where there is sufficient room at the bottom in blind holes.

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Bottoming Taps ( Finishing Tap) - This style, with a 1-2 thread chamfer, is made with just enough chamfer for starting in the hole; as the name implies, it is designed

Thanks to both of you. Great information! I've got the older, thinner, style exhaust flanges and I don’t think they could handle a 8mm anything. In the interest of saving more money I think I will give the stepped stud a try. If I was to use a coarse 8mm thread Helicoil, do you think it would take out to much material and prevent me from the eventual upgrade to a newer style 8mm stud/flange?

if you do not have luck with your trials...
then the way i have had to fix mine was taking the motor out and taking it to a local high referenced welder and having him run a gob of aluminum weld into the hole...then retap it

i tried putting a heli..it failed...i tried tapping for a another stud it crumbled when trying to put enough torque to tighten the header down.....in the end i had no material left to work with and a mayo jar full of coils , high heat epoxies,stepped up sized studs,and drill bits and taps...about 40-50 bucks worth..and 5 trips to the auto and hardware store.....then i had to go pay the welder to do it right...100 and the next day it was fixed for good...a week of buying stuff and wasting time later....

if i ever strip one again i will go straight to the welder and be done with it.....others here have had the same story or close...

@ trianglelaguna You just described the nightmare that I was seeing in my crystal ball. Thank you for sharing and allowing me to benefit from your experience. Perhaps looking at that mayo jar will be a little less painful now.

I’ve had some experience with threaded holes in aluminum motors but I’m treading into new territory with it being on my motorcycle. My first love has always been nitro methane/methanol powered radio controlled models. Helicopters, airplanes, boats, cars, trucks etc. Those motor blocks are so small that a stripped hole generally means replacing it.

So it looks like I get to crack open the motor….man I was trying to avoid that. That worries me. Not so much the tear down but the discovery of more parts that need replacing and then to get it all back together and working properly. Not to mention the special tools…..Its old and leaking oil so I suppose it needs to be done anyhow. Any advice on “must have” tools? I’ve never dealt with
4-stroke motors so the entire top end will be a learning experience. I do have a Chilton’s and a Clymer manual, they seem to be great at getting me within hand grenade range…..