Valves again

[street]

My supplier in NZ has now agreed to stop new valves order following 4 month issue. The machine shop appear to be technical and capable to work on head, I however do not know whether the work is required or not. I have had a good conversation with Steve at lotus marques and whilst I may follow all of the technical comments the approach to install larger diameter valves may lead to further issue down the line.
So here is the conundrum, I had blow by on two pistons and you could see exhaust debris on ex valves I do not know what the measurements of existing valves, shims etc are to confirm if they are actually in tolerance. The car would not run at all, but this was due to pistons and not valves in my
Opinion.
Is anyone capable of providing a list of the critical measurements I order to assess actual condition of head. Steve mentioned shims should be 125 thou ideally etc.
I am concerned that by cutting valve seats will lead to other problems in stem heights clearances etc. do I just complete grind on valves and reinstall.
Any help as I am between a real rock and hard place. Thanks

[rgh0]

Hard to summarise what's needed in a simple post. If you want to try to recut your existing valve seats and then fit suitable new valves then I need you to take some careful measurements accurate to at least 0.1 mm.

Unfortunately most people don't really understand how the valve train set up works so they cant advise anything but their "Standard" solution.

After that I can advise on what's possible or not for a "Non Standard" solution that will minimise cost without affecting reliability

Key measurements as follows

1. Existing valve lengths from face to top of stem for each valve
2. Existing distance from top of collet groove to top of valve stem for each valve
3. Current valve head Outside diameter
4. With existing valves seated in the head, distance from valve tip to cam base circle for each valve
5. Current cam base circle
6. Current follower shim pad thickness
7. Distance from tip of existing valves when seated to spring pocket base without spring seat in place for each valve.
8. Ideally also need valve guide inside diameters to determine if guides have excessive wear. This requires specialist small diameter bore diameter measurement accurate to 0.01mm top centre and bottom
9. Ideally also need follower sleeve diameter and bore diameter top centre and bottom to 0.01mm diameter to determine if followers and sleeves are Ok to reuse.


If uncertain about taking any of these measurements let me know items 8 and 9 not critical at this stage if you don't have the measurement tools. Some photos of the head combustion chambers with the valves in place and removed, photo of the valves themselves and photos of the other valve train components and valve spring pockets would also help determine whether other issues exist.

cheers
Rohan

[2cams70]

Did you confirm whether or not they had the technical capability to actually replace the seats if need be?
Last time you posted they were suggesting oversize valves in lieu of replacing the seats. Did you find out why?

[street]

Thanks Rohan, I will ask and Steve has volunteered to have a call with them.

The reason they are stating to recut seats is to allow longer valve stems and increase distance from collet groove to top of stem as they think this is close to minimum, I recall 1.8mm.

If the exhaust valves are still within tolerance why change anything else?

[2cams70]

The reason they are stating to recut seats is to allow longer valve stems and increase distance from collet groove to top of stem as they think this is close to minimum, I recall 1.8mm.

First they said you needed valves with bigger heads to bring the valve higher relative to the seat and so allow more clearance between the end of the valve stem and the camshaft. Now they are saying no longer any need to do that - you actually require valves with longer stems to bring the end of the valve stem closer to the camshaft.

Something doesn't sound right to me. With a good machine shop you shouldn't need to do all those measurements yourself. You should be able to trust them to know what they are doing.

[rgh0]

Happy to help with analysis and recommendations when I have some data. Otherwise I am just guessing which can be less than helpful

cheers
Rohan