Lotus Elan

Valve pocket depth measurement

PostPost by: jabingb » Sun Apr 05, 2020 2:51 am

I have a head that was I believe was used in a F3 car, it certainly is a big valve. It has no cams and I'd like to use a high lift profile, to that end I'd like to understand if the valve pockets are deep enough. How does one measure that, from what reference and what dimension should I have to use a .410" lift cam? Thx
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PostPost by: rgh0 » Sun Apr 05, 2020 3:13 am

With modern springs and modern thin followers you can use the standard depth valve spring pockets for up to 0.50 inch lift cams which is about the highest lift anyone fits, so these days no need to deepen the pockets and all the problems that went with that on breaking through into the inlet tracts which were normally ported to go with the bigger cams and valves.

If you have an old racing head it may have deeper pockets already and depending on the valve train components you select you may have to shim the valve spring seats to get the correct installed load.

The standard depth from the cam centre line to the spring pocket base is 2.10 inches / 53.3 mm, though this was not machined very accurately by Lotus and varies a bit from head to head and along individual heads from one end to the other. I made up a special tool that sits in the cam bearing carriers to measure that depth accurately. You can do a quick check by sitting a small metal rule on its edge in the bottom of the cam bearing carriers and measuring down from the top edge of the rule to the spring pocket base parallel to the valve angle, then subtract the rule width and add half the bearing carrier diameter to that measurement to get the height from the cam centre line.

What ever dimension you have, with the right selection of components, you will be able to fit a 0.410 lift cam OK. You just need to ensure you get the correct installed load and height for the springs selected and check a few other critical dimensions for clearance and spring load at full lift.

regards
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PostPost by: jabingb » Sun Apr 05, 2020 3:20 am

Thanks Rohan, was hoping you might chime it, will go measure in a few minutes but I guess it's a moot point. Jerry
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PostPost by: rgh0 » Sun Apr 05, 2020 3:31 am

Knowing this depth is the starting point for any non standard head rebuild. You need to know what it is when selecting the components you want to use and then assembling them to ensure you have a practical and reliable valve train set-up. Even for a standard rebuild it helps to know to ensure that the standard components purchased which are often not as accurate as desirable will fit properly.

cheers
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PostPost by: jabingb » Sun Apr 05, 2020 3:46 am

rgh0 wrote:Knowing this depth is the starting point for any non standard head rebuild. You need to know what it is when selecting the components you want to use and then assembling them to ensure you have a practical and reliable valve train set-up. Even for a standard rebuild it helps to know to ensure that the standard components purchased which are often not as accurate as desirable will fit properly.

cheers
Rohan

A mate, sadly no longer with us, gave me this tool years ago and I've never had an opportunity to use it until now. I measure ~ 2.060" so a little less than what you mention but probably good enough Will measure more accurately, tomorrow but suspect I'll be very close. Thx
IMG_7466.JPG and
Last edited by jabingb on Sun Apr 05, 2020 1:09 pm, edited 1 time in total.
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'65 S2 Elan 26R | '69 S4 Elan FHC | '00 S1 Elise Sport 190
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PostPost by: rgh0 » Sun Apr 05, 2020 4:17 am

Thats a fairly typical depth in a standard depth head. Check that all the pockets are the same. Then you need to decide what cam to use and what valve length, spring pack and followers to go with it.

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PostPost by: jabingb » Sun Apr 05, 2020 1:24 pm

rgh0 wrote:With modern springs and modern thin followers you can use the standard depth valve spring pockets for up to 0.50 inch lift cams which is about the highest lift anyone fits,
Rohan

Rohan, are these modern springs and thin followers common from most sources? What terminology should I use to call out my needs, thinking of the usual suspects here in the US?

The other issue that I realize I have is this head has some VERY unusual follower sleeve dimensions, 1.423" intake and 1.412" exhaust, that may preclude the thin followers you suggest? I may have to bite the bullet and replace the follower sleeves, not a task/expense I'd prefer. Thx
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PostPost by: vstibbard » Tue Apr 07, 2020 10:37 pm

Jerry, The Big Valve Brian Hart heads all had larger diameters buckets fitted, I think it became a common modification for racing heads in period to allow for the larger lifts, I've bought heads over here from period F2 cars which had been modified with larger diameter buckets.

I was told of source which from memory was a modified Alfa 105 bucket which had the skirt shortened.

With todays improved cam profiles and springs, for a light car like a 26R you could use QED 420's which many use on their road cars or even QED 450 or the McCoy 450 type cams.

Rohan has lots of experience with various cams and I'm sure would be able to give some tested options.

Cheers

Vaughan
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PostPost by: rgh0 » Wed Apr 08, 2020 2:55 am

jabingb wrote:
rgh0 wrote:With modern springs and modern thin followers you can use the standard depth valve spring pockets for up to 0.50 inch lift cams which is about the highest lift anyone fits,
Rohan

Rohan, are these modern springs and thin followers common from most sources? What terminology should I use to call out my needs, thinking of the usual suspects here in the US?

The other issue that I realize I have is this head has some VERY unusual follower sleeve dimensions, 1.423" intake and 1.412" exhaust, that may preclude the thin followers you suggest? I may have to bite the bullet and replace the follower sleeves, not a task/expense I'd prefer. Thx


The source i use currently for valves, followers and spring packs is Tony Ingram at lotus7.com. He has a range in stock that you can select from that will meet most engine build needs. I have got spring packs from most of the other suppliers e.g. - QED , Dave Bean, John McCoy and you can use them in some applications but generally I find the install dimensions and spring loads that match my needs best come from the ones that Tony Ingram supplies

Yes use of Alfa followers was common in modified engines in the old days. I don't know if they did it to accommodate the nose of a higher lift cam or for other reasons such as the Alfa followers being thinner and lighter or stronger than the cast iron Lotus originals. These days light weight steel followers can be had for the original sleeve bores and with a slightly longer skirt to accommodate the fact that they come up higher with the smaller base circle used on a high lift cam. You don't need a bigger diameter follower for the cams I have used up to 0.49 lift provided it is ground on the needed smaller base circle. You sometimes need to enlarge the half moon cutouts on either side of the sleeve to accommodate the nose of the high lift cams and this depends on the original size of these cut outs and that varies a little and the exact location of the lobes on the cam which also varies a little.

If building a modified engine with modern high lift cams there are a range to choose from depending on the bottom end build and rev limit you want to use and the application you are intending the engine for

regards
Rohan
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PostPost by: el-saturn » Wed Apr 08, 2020 5:17 pm

hi there: the basic questions with this material at hand:

two sets of big valves (both have diameters: 41,3 in / 36,5 or 35,60 out) the stems are 100,75 and 98.90

two sets of cams: one has 11,2mm lift and long duration (flater lobe)
the other has 10,7mm and shorter duration (pointy lobe)

one of the spring sets has been used with the 10,7mm cams and all of them shims (at bottom) stayed together with the springs and are numbered.
questions:

a) can i reuse the setupwith new valves as already used (i used the race length ones!) in another head using the same bits as before?
b) could i also use the 11,2 cams using the 10,7 setup as already used or would i need new springs?
c) what would the disadvantage of using the shorter valves be O R do both above lifts require the longer valves??
tx sandy
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