The V8 Owners Forum -

I'm just building a new 4.6 cross bolted engine. Well I bought the block already balanced and built. It's a V8 Developments engine. I have some Thor 4.6 heads to go with it. I have had the heads skimmed 8 thou to clean them up and have had the valves re-cut and all the valve heights set.
I have measured the heads and valve heights againt a standard 3500 head, and the difference is only around 12 thou.
I have bought adjustable moly rods to fit which I know are longer to allow for trimming down to suit. To get a reference length, I fitted a set of new standard rods, the same ones I use in the 3500. Now when I fit the standard rods in the 3500 I have to shim the rocker pedestals a little to get my average pre load set. But I only have to use around 20 thou of shims.

When I fitted the heads with new comp gaskets and new standard rods, the pre load with the lifter on the heel of the cam was around 380 thou???

I have measured the distance between the centre of the cam and the bottom of the heads as a reference on the 4.6 and the 3.5 and give or take a few thou they seem the same.

Would the Blower cam and the Typhoon cam have such a big difference on the heel? I thought the heel would be the same height on all the various cams.

I'm having the rods cut to suit the new measurment as all seems ok. I could turn the engine with a socket on the crank and it moved freely without any apparent binding, so I assume the valves are not hitting the pistons.

Also, can I take the heads off and re use the comp gaskets as the engine has not been fired. I will of course make sure they go back on exactly how they are now,ie same way up and same side.

I have built up three 3500's and they have all accepted standard rods with minimal shimming required??

Any ideas chaps.

I think your preload difference is down to the 3500 using tin gaskets and the 4.6 would use composites which are much thicker and thus increasing the distance between the rockers and the lifters. (just re-read this and I got this the wrong way round, this would reduce your preload, erm!)

Do not re-use the gaskets even though the engine has not be run you have torqued the heads down and that has compressed the gasket. Just think of the hassle of trying to save £20-£30 versus stripping the top of the engine down again after a gasket blows.

Turning the engine over by hand is not assurance that you have sufficient clearance between you valves and pistons. For a few reasons, 1) Your lifters will not be pumped up. Once they are pumped this reduce the clearance, 2) when the engine is running various components will expand, the valves, pistons, etc.

The valve-piston clearance is performed using solid lifters or the old trick of filling an hydrolic lifter with washers.

My engine sounds similar to yours, it is a 46D I have a piper cam 285i (0.477" lift) installed and stage III heads with composite gaskets and I performed a clearance test and saw a 80thou clearance on the inlet valves and 116thou on exhaust.

recommended minimum clearance is 80thous for inlet and 100 for exhaust (more expansion for exhaust)

Cheers Adam
Yes I got that wrong a bit. I meant the engine turned over ok witht he rods in dry lifters, but with a pre load of 380 thou. I meant I was happy that they had not touched down. I dread to think what would have happened if nI hadnt checked and then started the engine.

Interesting point on the pre loads there mate. Real Steel say set all valves to a 60 thou pre load. Or by clearance are you talking valve/piston clearance?

How did you measure your valve/piston clearance? I've lent my dial gauges to a mate and wont see them for a few weeks now.

I was talking minimum valve to piston clearance. 60 thou preload is usually for Rhoads or pump up lifters. I think nornal lifters are usually set to 20thou or so.

I measured mine by installing heads with checking springs which are stronger enough not to allow the valve to drop but weak enough for you to push the valve down by hand until it contacts the piston heads in the danger areas of the timing cycle. In this way you can work out the clearance at any given time, usually you take readings every 2 degrees. If you just want to check the minimum clearance irrespective of where it occurs in the cycle then you can place plasticine on the cylinders but use some oil and talcum powder you can stop the valves sticking to the plasticine. You then turn over the engine by hand 720 degrees with the normal valve springs. Then remove the heads and you can see the depressions and measure with a depth guage. Both methods waste a head gasket but cheap compared to wrecking the engine.

Cheers Adam
I've got a set of check springs for setting my spring heights. I'll give it a go when I get my dial gauges and mag block back.