need machinist opinion on repairing torn threads

electrofelix

Have a car that I've done a cylinder head replacement, however when putting the valve cover back onto the engine I discovered that some of the holes for the bolts that hold the valve cover in place have had the threads stripped on them.

Yeah, I should have made sure the machine shop checked them before returning the head to me, but that was then and this is now, and I would rather not dismantle the engine for a second time.

It looks like the holes are actually thread inserts that are in large holes. This is probably because the head is aluminium and having to replace the valve gasket every so often would result in aluminium threads being stripped very quickly by steel bolts.

Question, is it possible to extract these inserts and replace them without having to remove the head from the car?

For those wondering why I need the valve cover to sit on pretty tight, it's because otherwise a small amount of oil will leak out between the cylinder head and the rubber seal between the head and valve cover, will drip onto the exhaust manifold and result in black smoke filling the engine compartment. Which is also where the air to the a/c unit is taken from. And burning oil is somewhat hazardous.

phelixoflaherty

you can drill out the old thread re tap the hole for a heli coil. Its like a spring but is in fact a thread.
A set for one thread size is pricy.
Most engineering workshops would have them.
Bring the bolt too, to get a size off it

Like this:
http://cgi.ebay.ie/M12-x-1-75mm-Metric-Thread-Repair-Kit-Heli-12mm-Coils_W0QQitemZ150269345581QQcmdZViewItemQQptZLH_DefaultDomain_3?hash=item150269345581&_trksid=p3286.c0.m14&_trkparms=72%3A1301%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318

phelixoflaherty

Just re read post. if you can prize out the start of the insert it should pull out with a pliers.
if the hole and thread is too worn the only thing you can do is thread the hole to the next biggest size. ie. M6--> M8

bushy...

electrofelix wrote: »

It looks like the holes are actually thread inserts that are in large holes. This is probably because the head is aluminium and having to replace the valve gasket every so often would result in aluminium threads being stripped very quickly by steel bolts.

Question, is it possible to extract these inserts and replace them without having to remove the head from the car?

For those wondering why I need the valve cover to sit on pretty tight, it's because otherwise a small amount of oil will leak out between the cylinder head and the rubber seal between the head and valve cover, will drip onto the exhaust manifold and result in black smoke filling the engine compartment. Which is also where the air to the a/c unit is taken from. And burning oil is somewhat hazardous.

You need to suss which type of insert it is before you go at it.

There are 3 main types ,
one is like a tiny (usually stainless steel) spring ,



next is kinda like a small piece of bolt that has been drilled through



other is like the above but not threaded on the outside, just cooled and pushed into the alloy


If its the first kind as said above you might be able to catch the top and encourage it out.

If its the second you might be able to get it out by threading in say something like a 3 inch long allen headed bolt with a locknut thats been ground down a bit. Don't try too hard since it probably won't work ,but may be worth a try.

If you are drilling it out , get left handed drill bits and a decent drill.

Other ways to kill it might be acid (one that wont attack the alloy )

quietsailor

Other ways to kill it might be acid (one that wont attack the alloy

Be very, very careful using acid around aluminium, I've heard of cases where acid used to remove enamel off centrifuge discs was used to try and clean an aluminiulm head, when the engineer came back the next morning all that was left was the steel springs, valves, guides and seats :eek:

Can you take a picture of the insert and put it in the thread, we'd be better able to advise you that way

bushy...

quietsailor wrote: »

Other ways to kill it might be acid (one that wont attack the alloy

Be very, very careful using acid around aluminium, I've heard of cases where acid used to remove enamel off centrifuge discs was used to try and clean an aluminiulm head, when the engineer came back the next morning all that was left was the steel springs, valves, guides and seats :eek:

Can you take a picture of the insert and put it in the thread, we'd be better able to advise you that way

I finished that post in a hurry , i should have said use something that will attack the insert and not the alloy.