The V8 Owners Forum -

Hi

On the rebuild one of the rocker shaft pedestal bolts failed to torque - all others went in fine but one isn't feeling good.

Gutted. Checked out the wrench, clean threads, pedestal seated OK, everything I can think of - bolt left 'as is' whilst I go and figure this out.

I might be facing a thread repair with this - the bolts have the part number 602097 and are listed as 3/8 UNF x 2.79 which confused me with the '2.79' part as there's nothing listed from what I can see by way of a helicoil repair if I need it.

Does anyone know the thread size and pitch?

Thanks in advance.

If into ally, they'll be UNC?

I'm sure they are UNC. Probably 5/16ths.

Chris.

I did the job last year, and used one of these - http://www.ebay.co.uk/itm/3-8-UNC-Helic ... SwofxUdcNm

Worked a treat

Brilliant!!!

Thanks for the posts guys - much appreciated, and it's very comforting to hear from someone who has successfully sorted out the same problem.

The bolt details I found from the part number had led me off the track with UNF, explains why I couldn't find anything.

Kit ordered, very happy!

This is how I did it, nicked this from another forum

"Well here's the helicoil and the bit of head that I unscrewed from the bolt



Drilled out the old thread to the correct size and tapped the hole for the helicoil



Helicoil fitted, pleased with that



I fitted one years ago and made a right pig's ear of it so I was very careful. I put the bolts in either side so I could see the angle I needed, then put some tape around them to make them the same size as the drill bit. Then clamped a straight edge between the two bolts so that I knew the angle would be spot on if the drill bit touched it when drilling. (I hope that makes senses ?)

I open out a plastic bag and put a small slit in it then, forced it over the pedestal so it was tight, then tapes it into position.

Then drill a bit, vacuum, drill a bit vacuum etc

Used plenty of cutting fluid and time. Worked a treat "

I used the same kit recently to repair the clutch slave mounting threads in the bellhousing (a previous owner had clearly thought that 5/16UNC and M8 were the same thing). It worked well at the second attempt - first time the helicoil was a bugger to get in and jammed the tool which led to all sorts of expletives and wrestling to get it back out... When I checked, the supplied drill was about 0.1mm undersize. Once the tapped thread was drilled out with the right size (which was "fun") the helicoil went in fine and all was good.

So, from my experience, if the helicoil is not going in easily and smoothly, check the drill size.

I've used that kit, never had a problem with it

Burbling wrote:I might be facing a thread repair with this - the bolts have the part number 602097 and are listed as 3/8 UNF x 2.79 which confused me with the '2.79' part as there's nothing listed from what I can see by way of a helicoil repair if I need it.

Does anyone know the thread size and pitch?

Thanks in advance.

The 2,79 is probably the length of the bolt.
3/8 is the diameter and UNF is the thread pitch.

Update - Not what I expected either.

I removed the bolt and found no thread swarf or debris there at all.

Checked the head thread and clean as a whistle, no damage evident. Cleaned the thread out and carefully tried another pedestal bolt by hand, which went in fine. Checked the original bolt then by hand and felt a slight distortion in the bolt as it went in, and watching could see a slight distortion in the bolt - head off true as it turned.

So, looks like the bolt is buggered? I was very careful with my tongue (35Nm) so figure it's something I have inherited from a previous build in the engine's past.

New bolt going to be ordered but I'm taking the other shaft off and checking all those bolts again - might for peace of mind get a new set of pedestal bolt, £4 each and to my mind worth the spend to get rid of any doubts about the last fitting of the rocker shafts.

Heads look fine though, which was a relief......

Stick the bolt half an inch into a drill chuck and run it slowly, you will soon see if the bolt is straight or not.

The rocker shaft bolts are 3/8 UNC no question not UNF