4 bolt camshaft sprocket

[trackerjack]

Just recently someone has asked me about whether I think the 2 measly 1/4 UNF bolts that hold the cam sprocket on are enough?
Well some years ago at Thruxton I saw a racer brought to an expensive engine fail stop and I found out that the engine built by the well known puzzle maker had broken these bolts and the valves had become intimate with the pistons
So when I built my engine I added 2 more M6 bolts (chosen thread to avoid any incorrect assembly) to give peace of mind on a possible fault.
The picture shows a cam sprocket and cam with my drill jig to locate the holes without hitting any vital bits such as the cut out on the cam (correctly spotted Chris).
The jig is used to drill the cam using a pistol drill as the thickness of the jig keeps the drill square to the face and there are two holes to attach the sprocket to the jig to spot that too. I found that the cam is soft and easy to drill and tap.
Eagle eyed spotters among you will see the spigot that sits in the sprocket and locates in the cam is missing as I had not got one when doing the picture.

The next picture shows one of the adjustable cam sprockets that I made a few years ago.

Finally the bottom picture shows my set up when I did the first one.

[sprintchris]

Very nice Jon,

Looks like a nice template that you made there.

It's definitely the way forward adding a couple more bolts. I do like the idea of using metric too as there seems to be a much broader selection of bolt types to choose from.

I'll post some pics when I get mine back, but we did notice with the new Kent pulley, the two 1/4 inch bolts had a lot of slack, the pulley holes could be quite a bit smaller, my machinest chap said we could take the holes up to the next closest size so they all sit snug in the pulley.

Roll on a week or so....just want to get this built up now!

[trackerjack]

Well if nothing else it will be one less thing to kill the poor old sprint engine
In the last two years I have come across an engine that someone had put a stainless bolt in place of the correct high tensile ones and these are not as strong and should not be used for these type of bolting and overtightening or under tightening can both wreck an engine.
It will be fine when done Chris and give years of loyal service.

[sprintchris]

Pulley all done.

Explained to the engineer chap the issue, unable to space four bolts evenly he six bolted it.

The two original holes in the pulley where much too big for the little 1/4 inch bolts to the point the Allen bolts didn't have a lot of surface area to grip, so I've shaved down the original tab washer to fit around the Allen bolts and put two original hex headed ones in, all fits well and grateful for everyone's advice.

Also, the Kent pulley, I notice the adjustable slots aren't uniform, no matter how you assemble the two bits one of the slots is near the end of adjustment. It does seem to have set up ok.

P.s I haven't forgotten to bend over the locking tabs!