tapping e50 cylinder stud holes to m7

i unfortunately stripped out a hole where the cylinder stud bolts into on my e50. i've tapped it to m7 now, but am having trouble fitting a m7 stud through my cylinder/head. my buddy as a garrelli, and i tried using one of his studs, and it wouldn't fit through my cylinder or head. treats has a few options:

this first one seem to have pretty piss poor reviews, so i feel like i should stay away from it:

M6 to M7 Cylinder Studs

this one seems more promising for what i need, and seemingly more reliable:

Tomos M6 to M7 studs


here lies my question(s):

will either of these even fit through my cylinder/head?

will the length of the tomos studs be a problem when reassembling everything?

is drilling the holes in the cylinder/head to be a bit wider a bad idea?

if anyone has had to tap an e50 from m6 to m7, i would love to hear how you solved this issue. the first link is an appropriate length, but i'm weary after reading the reviews. the second, i'm concerned about the length being too long. above everything, i'm concerned the diameter for both is too wide.

plz halp.


Re: tapping e50 cylinder stud holes to m7

also, yes, i did my homework on this topic, but it doesn't seem that anyone has addressed these topics in similar posts from the past.

Re: tapping e50 cylinder stud holes to m7

there are two ways to make threads, cutting them or pressing/rolling them. cutting them leaves sharp bottoms and stresses that actually weaken the threads so they're much easier to strip. Some of that can be recouped by heat treating, but its not often done. I think alotta these convenience aftermarket studs are made by machine shops just by cutting and not treating because those are the tools available to the machinist. They will strip more easily and most of the time probably wont hold up to factory torques. You can remedy that somewhat by using long coupler nuts or brass nuts to distribute the load over more threads. Cutting also means the shaft diameter is the same as the max OD of the threads, so theyre wider (and heavier)

the OEM ones and most proper studs and higher grade hardware, the threads are pressed or rolled in, which creates stresses that strengthen the threads. They also have by default a thinner shaft because the threads are swuished out and pressed in, the main body diameter is halfway between the outer diameter and the bottom diameter of the threads. Its also cheaper, but requires specialty tools.

The end result? when you buy aftermarket or machineshop made studs they're cut threads and much weaker threading. The factory and OEM are almost always rolled and both stronger and have thinner body shaft diameter.

TLDR: Get the tomos, they'll fit. the other ones are less likely to fit and also weaker.

In my personal experience I've had luck with using an M7 to m6 helicoil after tapping out the cases (this is my goto) and you can also easily drill out the hole in the cylinder and head to 7mm if needed for a full M7 stud. but those tomos ones should work as is.

Re: tapping e50 cylinder stud holes to m7

^ this was very informative for me, thank you will

Re: tapping e50 cylinder stud holes to m7

Brad William /

Thank you btbw. I thought I was pretty well informed on this. you taught me some there.

Re: tapping e50 cylinder stud holes to m7

U need a drill press and make sure the cylinder and then the head is flat on the drill press. Get an appropriate size drill bit to accommodate the m7 stud and drill both the cylinder and the head to that. I do this on hobbit builds but there isn't usually enough material on e 50 cases to do all four so I would stick to the single stud u stripped. My assumption is that u already drilled the case. If u did the case and u enlarged the stud hole without freehanding the overdrilling ( as in u retapped the m6 to m7 without first drilling it , then I assume the hole is at a perfect right angle to the case. Just to be certain put the stud in and make sure it is at 90 degrees to the top of the case. If u freedrilled it , then oh oh

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