1995 850 T5-R Stripped head bolt

Cincyken · Post by **Cincyken** » 24 May 2015, 11:32

I had a burnt exhaust valve and pulled the head. After I got the head back from the machine shop, I remounted the head using new head bolts. While torqueing the head bolts down, one of them let go. I took the bolt back out and found the bolt was fine but there were metal pieces in the bolts threads from the block threads. I cannot get the bolt to hold at more than 30ft-lbs force. I have been a back yard mechanic for 50 years and have never stripped a head bolt. What are my options?

Post by **abscate** » 24 May 2015, 12:12

I think towing the car to a machine shop and having them put in a Helicoil into your block is probably fastest/easiest solution. They don't look hard to do but Ive only done them on air cooled VW blocks, not on a 'real engine'

Post by **Ozark Lee** » 24 May 2015, 21:10

Putting in a Helicoil is not at all tough but the head will need to come back off to do it right. You could drill though the head and tap both the head and the block to get the coil though the head and into the block but that is pretty sloppy.

...Lee

Post by **abscate** » 25 May 2015, 04:11

Head should come off, I agree.

Cincyken · Post by **Cincyken** » 25 May 2015, 11:52

I have never used a Helicoil. Can it withstand the kind of stress that will be placed on it when I am torqueing the head back on. The way Volvo recommends torques a head on, it takes the head bolts almost into plastic deformation. A lot of stress (probably close to 120 ft-lbs of torque).

Post by **Ozark Lee** » 25 May 2015, 14:56

A Helicoil can take more than aluminum that it is threaded into can. It is basically a steel threaded insert. You drill out the existing hole and tap it to the OD of the Helicoil, screw the coil into those threads, and then it replicates the original threads on the inside of the coil.

They typically sell them with a special tap and drill bit so that you get the newly sized hole right.

...Lee

Post by **precopster** » 26 May 2015, 14:04

A time-sert may be more what you're looking for. It is a one-piece thread system that avoids the segmented smaller lengths of a helicoil-perfect for head applications.

Post by **JDS60R** » 26 May 2015, 16:20

Yes and time-sert can give you different lengths as well.

Post by **precopster** » 27 May 2015, 04:31

Boom boom

Post by **JimBee** » 27 May 2015, 10:25

When I had an 850 head off last fall, I followed the advice of an engine rebuilder concerning cleaning out the bolt holes. Some of the original bolts had a build-up of corrosion and oily gunk. I sprayed engine degreaser into the holes, ran a clean bolt gently in and out using my drill with socket, then wicked out the residue with some oversize pipe cleaners from the Dollar Store. Several holes needed repeat treatments, making sure to clean the bolt each time and remove all liquid. This treatment probably added an hour to the job and I think helped ensure against poor thread grip.

Also, while you have the head off, use a tap to clean out your water pipe flange threads on the "front" firewall side of the head.Those holes will have a buildup of either thread lock or sealant which can cause bottoming of your new bolt (or the wirebrush cleaned original) before the flange is tight when you reassemble. I didn't do that and ended up borrowing an adapter from a local shop which they were gracious enough to loan to run a tap into that hole. Even then I couldn't get the tap to the end of the bolt hole because of the tapered tip. You DO NOT want to strip that hole. I believe the tap is 7mm. Menards has them. Bring in your bolt to be sure.