Valve Stem Height

[Esprit2]

Does anyone know the Lotus factory spec for the valve stem height in:
1) the Lotus Twin Cam Ford cylinder heads?

A little off topic for this group, but while you're at it...
2) the Lotus 9XX cylinder heads (907, 910, 911, 912, 920)?

In the attached Jpeg, dimension 'A' (lower right corner) is just an example of what I'm after (it's for a Porsche 911). it's the distance from the spring well floor to top of valve stem. A 'good' machine shop would re-cut the valve stems as required after installing new valves or re-cutting the valve seats.

If you don't have the factory spec, do you have a disassembled bare head (a good one) you can measure? Insert a valve and hold it firmly up against it's valve seat. Then measure from the 'floor' of the spring well (where the spring sits) up to the top of the valve stem.

I know, I know... any 50-ish year old head has been around the block enough times that measuring will produce iffy results. However, at the moment I have 'no' results, and 'iffy' would be a step in the right direction. Of course, the factory spec would be great!

Thanks,
Tim Engel

[Esprit2]

Okay, I've answered my own question. Or more correctly, Ken at Dave Bean answered it.

The Twin Cam head cross-section illustration on the attached page (from Dave Bean's catalog) indirectly gives the dimensions for the height of the end of the valve stem above the floor of the spring well.

D = distance from cam centerline to end of the valve stem.

E = distance from cam CL to floor of spring well.

E - D = distance from floor of spring well up to end of the valve stem.

Regards,
Tim Engel

[rgh0]

I would be careful about using the bottom of the valve spring pocket as a reference as they are not machined very accurately on many heads and can vary along the length of the head versus the cam centreline. While the nominal standard is 2.1 inches from cam centreline to spring pocket base it can vary by +/- 0.1 inch / 2.5 mm which can give you problems if you set your valve tips to a constant number versus the spring pocket base

I always use the cam centre line as my reference for the valve train set up at that is a stable and the most relevant reference point. I have never seen any "official" factory dimensions for the valve train set up but you can reverse engineer most of it from the standard dimensions of most of the components. i have attached a pdf of the "standard dimensions" I use as reference based on this reverse engineering.

You will note that these dimensions are the same as shown in the DB manual for valve tip and spring pocket base and that DB also uses the cam centreline as the reference point not the spring pocket base

Big valve std dimensions2.pdf

(23.19 KiB) Downloaded 226 times

cheers
Rohan

[Esprit2]

Thanks, Rohan.

Tim

[rgh0]

I have a couple of spare 907 / 912 heads and one day I will calculate the same dimensions for those as for the twin cam when I have a little time

cheers
Rohan

[Esprit2]

Rohan,

Well, hurry up and make some time...

Tim

[rgh0]

I am planning on retiring from my day job at the end of September this year. But people tell me I will be busier when retired than when I was working But I will find some time sooner rather than later!