ARP Head Bolt Clearance

[CG901]

I have an early Mk 1 twincam and bought a set of ARP head bolts to replace the originals. On the left front bolt, with the cut washer, the bolt is contacting the camshaft. I am wondering if I should grind off the circumference of the bolt head or is there another solution? First time doing this. Here is a top view of the problem. Thanks.

[Foxie]

You could get the cam locating disc diameter reduced.

However, progressive judicious and careful grinding of the bolt head flange will work. A little bit at a time !

[2cams70]

That's interesting. I've got a set of the same bolts for my Twin Cam although I haven't gotten to the stage of fitting the head to the block yet - been distracted with other projects. Did you get these bolts from Tony Ingram? (I did). Suggest you contact him for advice. I'd be interested to know what he says.

[2cams70]

I expect the solution may be to fit the head and then the camshaft (not the head with the cams preassembled as one unit). A pain though and not ideal.

[CG901]

Yes, got them from Tony, but he hasn't replied yet. I hadn't ever heard that shaving the ARP bolt head was necessary, but it definitely is too close to the cam here. Will be removing bolt head material in small increments until I get safe clearance.

[rgh0]

The clearance is very tight and i have got out the feeler gauges to measure it when assembling engines before. I have never had to turn down the flange on the bolt head but it could certainly be possibly needed. With slight variation in the cam centreline and bolt hole location you could easily get them to clash. You don't need much clearance as neither the cam or bolt are going to move much in location once assembled.

cheers
Rohan

[RichardHawkins]

I didn't realise that ARP offered head bolts. I bought ARP head studs via Burton Performance, and then discovered that the studs would not pass through the head and also align with the block. After ages with an adjustable reamer I managed to get sufficient clearance to fit the studs without binding in the head.

My studs came with thick (about 3-4mm) washers that require a flat filed on them in the position you show in the photograph so as not to bind on the cam thrust diameter. Fitting these washers raises the position of the nut so that it does not bind on the cam. I cannot see a washer beneath your bolt head. I think it is standard to have thick washers under all the bolts in order the spread the bolt load over a larger area of the head and prevent the aluminium yielding (collapsing) under the bolt load.

I was unable to stop the thick washer, with the flat filed on it, from turning and binding on the cam as I tightened the stud. I jammed a piece of shim between the washer and the cam then tightened the stud, and finally pulled out the piece of shim. This resulted in clearance.

Richard Hawkins

[CG901]

Thanks Richard Hawkins. If you look closely, you will see the ARP thick washer beneath the bolt head. Two of the ARP washers came cut as is required. Even when placing the cut so the washer will not touch the cam guilde, the bolt head still touches. Thsi will require some head shaving to clear. I am not sure that ARP still make the bolts, as these were sourced from Tony Ingram who had some NOS available.

[2cams70]

Pictures of standard and ARP bolts attached. I chose these bolts in preference to studs because I don't really like the fact that with the studs you need to use a higher than standard fastening torque. I figure the deck face on the block and head and the threads in the block were designed for a specific clamping force. Anything higher could potentially cause distortion. Also with a road engine going through many hot/cold cycles you need something with a bit of elasticity. Plus with these you don't need to ream the holes in the head. With an alloy block studs are good, cast iron block I'm not so sure.

I'll get one of the bolt heads turned in a lathe if interference with the cam is a problem.