The V8 Owners Forum -

Rossco wrote:
I cut the pockets on Tony's pistons and the valve pockets just broke out the circumference of the piston. Acknowledged that the heads are TA so the valves are mahoosive and I did cut them 50.4mm diameter.

Spent a few more day thinking about this.....

So I've done some meaurements with a DTI on each valve to check the clearance more accurately.

Setting my lifters to no preload and adjustable pushrods to the same.

I then found the point at which the piston moves the valve on the up stroke and its 30degc BTDC.

Setting the dti at the point of highest lift on the cam to zero, and then pushing the valve down till it touches the piston and taking the reading.

Done this for 30BTDC to 30ATDC on both valves.

Exhaust has minimum of 6.5mm clearance at 5deg BTDC

Inlet has minimum of 0.40mm clearance at 10deg ATDC

so I need to get the cutout of each piston to allow the inlet valve to use the full depth, which should give me 4-5mm clearance in the end at a guess.

But what I'm not sure of is how much radial clearance I should be aiming for around the outer edge of the valve to the piston cutout?.....any ideas anyone.

Do I use the same as the minimum clearance of about 2.5mm.....which means I have quite a lot of material to remove.....so no way will the engine still be in balance after doing that on 8off pistons.

thanks all

scott

I would say at least 1mm of radial clearance. Unless the guides are insanely worn, it should never be anywhere near that

Have you spoken to chesman's about it yet?

no I've not spoken to them yet....

I wanted to be absolutely sure I was right, and I knew all the facts before I speak to them.

I'm back in Coventry in two weeks, so if I need to take anything it can do it then.

I just need to complete a few more checks on each piston/valve/cylinder to make sure they are all the same, then I should be ready to talk to them.

Just didn't want to make sure I was wrong....as nothing worse than that.

regards

scott

Balancing may not be an issue at all. How much is the additional material removed in grams ? I don´t expect it to weight that much. In any case, you are expected to machine the same amount each piston.

As for reciprocal weight, have a look at overbalancing/underbalancing at http://www.hotrod.com/articles/ctrp-050 ... rminology/