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MG MGF Technical - Cam bolts

Can anyone tell me what the specifications are for the cam bolts on the F - I Understand that the original ones are not vey good. Should they be replaced with stainless or high tensile bolts?

David
David

Hi David,
The original bolts on the VVC is "ATLAS 10.9" that should be fine if the bolt was up to that standard!
Bolts are defined into groups of material and strength.An ordinary cheap bolt is usually 8.8 and then it gets "better" by higher numbers. The bolts in the package from Mike is if I remember right in the 13īs and has a special surface treatment, so should be more than enough. DO NOT use stainless steel bolts as they have not the required data in this application.
Mikeīs kit includes all hardware + locking fluid +instructions and is IMO well worth the price. / Carl.
Carl

David

Another Kiwi here

Tried your email address but it bounced back.

The standard bolts are more than adequate. There is a problem with them coming loose, but not breaking. The main reason they come loose is that there is nothing locking them (standard practice these days - modern technology doesn't always go forward!) together with unusual harmonics in the VVC valve train (ever noticed the damped cam gear on the exhaust cam?).

Some engine builders, having heard there is a problem with the bolts slackening off, over tighten them. This can cause them to break.

Simple solution - lock the bolts with a good grade of loctite and torque them down to the correct figure. End of problem.

Paul
Paul Walbran

The bolts simply shear off slightly below the head!
I agree that this can be due to no locking agent have been used as well as repeated harmonic forces,but still the head of the bolt should stay on.
When you have exchanged the bolts for new ones , do a small experiment! Clamp the threades portion of one bolt in a heavy vice. Apply a ring spanner with an extension and apply force (or better a torque wrench with a scale and pointer). At what torque does the Atlas 10.9 bolt taken from a -96/-97 VVC shear?? Yes, a bit worrying....../ Carl.
Carl

Carl
We've handled a lot of these, and when torqued to the correct figure have never seen a problem. Problem comes when people over tighten them at some stage to "stop them coming loose", then they get weakened. After that, breaking is only a matter of time.
If you want to do a relevant test, do it to a new standard spec bolt. No use testing an old one that someone has had a go at.
Paul

Paul

David - yet another kiwi here, if you take your F to any MG Rover dealer all they will do is check the bolts are torqued correctly and loctite them. I had this done to my VVC when I bought it with 24,000km recorded. It now has 75,000km recorded three yrs later and the bolts are still fine. If you haven't had them checked, get it done ASAP - its cheap and will give you peace of mind as well as saving $$$ if they fail!
Mike

I had new standard cam bolts tested by Atlas a few years ago after a customer had catastrophic bolt failure..they said the bolt was not the right specification, tensile strength, surface finish or quality, for the application..in their opinion and they recommended another type. I have the report somewhere..The parmeters of the bolts tested were outside their recommended specifications ie not sufficient factor of safety hence some fail some don't. Re-using the bolts or incorrect torque load reduce the safety margin dramatically. The problem being that the end user specifies a bolt type and they supply, they do not get involved with design unless asked.
mike

This thread was discussed between 08/08/2005 and 15/08/2005

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