Broken exhaust head stud
 

Hi all

what would you say is the minimum I could get away with fixing after finding a broken exhaust head stud, not best moment, financially speaking and need to get car on the road

thankshttp://forums.pelicanparts.com/uploa...1483144475.JPG
http://forums.pelicanparts.com/uploa...1483144475.JPG
http://forums.pelicanparts.com/uploa...1483144475.JPG
http://forums.pelicanparts.com/uploa...1483144475.JPG

Mmmm, that's a lot of stud in the hand.
Broken short to the case.
Bruce

Ouch, Divalar, you will need to strip down that side at a minimum to the case to access the broken stud and drill it out. Measure everything and put her back together as hopefully a repair only. But most likely other studs are ready to go, so, you need to really consider a top end or complete rebuild. Sorry to write :-(

Let's say you only do the replacement of the stud, the head may be fretted, it may not seal properly, so you will need to machine it, well the other two being taller will affect your Cam housing and most likely you will create a tight engine situation and damage the cam or worse, other components in the engine and destroy it. Again sorry OP, for sounding so negative but I hate for you to do a repair and damage the engine further.

Something about these photographs looks wrong.

1. Why does the stud protrude from the end of the nut ?

This would have prevented the nut from being tightened.

If the nut wasn't tight why has the stud broken as there wouldn't have been any preload.

It has obviously been broken for some time as the washer is also quite rusty.

Mine broke off close to the case like that. I had a struggle removing the remnant. Had to dremel a slot in it and with a lot of heat and an impact driver finally got it out. I removed the rest of the lower studs, both sides. Also got the heads refreshed. Still not back together yet.


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thanks all for the info, doesn't look like a quick fix at all

all the best in the new year to everyone

To answer your question, of what you can get away with in terms of not fixing (i.e fixing as little as possiable).

Basically if its jus the one stud on that cylinder, then just finish what you were doing with the engine out, put the engine back in the car and just drive it - yes you are doing long term (and even short term) damage to the cylinder, and head. The head should machine out the cylinder will be trashed. It will probally over heat the guides on that cylinder too maybe, but you can still drive it. If two or more studs on the same cylinder are gone, then things are even more short term.

Basically you are into a full rebuild anway, and certainly will need one cylinder which might end up being the whole set, so if funds are tight, just finish what you started and keep it on the road until time and cash allow you to pull the engine apart.

I put another 2000 miles on a car with a broken stud, then pulled it and rebuilt it, as predicted the cylinder was trashed, but the head machined out fine, and I had to do the guides anyway (and replaced the cylinder set etc etc)

I'm sorry but this advice is completely wrong. I do not understand how anyone could suggest to do such a thing. If you don't have the money to fix it take the bus!!!

You have damage already and to stop now will limit the damage. To continue as suggested will continue the damage and probably increase the cost of the repair.

I bought my 83 911SC in 2003. Drove it for 10 years, less than 1000 miles/year. After 10 years, I started chasing an oil leak and discovered a broken head bolt that had been rattling around for a while. And then, another broken head bolt that was missing the broken part. A PO had known about the issue and not only ignored it, but concealed the evidence.

$4000+ and 3 1/2 years later, I'm getting close to trying to fire it up, hopefully tomorrow.

I figured I might get flamed for that, the point was, absolutely continuing to drive will increase the cost of the repair, in that as I said, it will take the cylinder with it, possibly leading to a full set, at rebuild time. Head of course maybe too.

However this question has been asked time and time and time again, and there are plenty of people running around either knowingly or unknowingly with a broken head stud or more.

In some cases the damage is already done, and as long as the owner is aware that the longer its run like that the more it may cost, its acceptable on that basis.

The question of the topic, was what was the least he could fix, which in his exact case is probably best answered as nothing until he is prepared to do it properly with a full engine rebuild (as the stud is snapped deep).

I personally wouldn't let it stop me from keeping a car as a "runner". The longer a car is apart the longer it will take to put back together. Sometimes decades.

I'm sorry but this advice is complete hyperbole:

Contemporary counterexample:

http://forums.pelicanparts.com/911-engine-rebuilding-forum/923220-80sc-row-rebuild-8-broken-lower-head-studs-200k-km.html

From that thread, a post of interest: "...the sealing surfaces of all 6 heads were in decent shape; only needed to remove 0.006" to clean them up."

http://forums.pelicanparts.com/uploa...1483144475.JPG

Hmmm, very interesting observation. Maybe OP will be lucky and the case side is not in all the way for whatever reason. Agreed, no way you can get a proper tool on the barrel nut.

Wow.

Once it broke, there was nothing to clamp the nut to the bolt. I wonder if, while rattling around in it's hole, the nut simply walked up the threads from the vibrations. Hey babinuk, was that barrel nut finger loose?


http://forums.pelicanparts.com/uploa...1483144475.JPG

Don't you mean down the threads :)

Once it failed there wouldn't be much vibration to let the nut move around.

Vibration will work with gravity over time to allow the stud to wiggle through the nut.

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