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Valve clearances


glynherron

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Hi All

I'm slowly rebuilding the motor of my s4s. Just refitted the head after having new valve guides and the seats recut.

I measured the shims before fitting the cam carriers hoping to measure the valve clearances and buy a few shims.

Unfortunately almost all valves have zero clearance. I have attached a link to a Dropbox photo if it works. It shoes my rough notes of shim thickness and the valve clearance.

What is my next step as I can't order new shims when I can't measure the clearance?

Does anyone in the UK have shims I could borrow? When I buy my new ones I could add my used ones to the library!

Thoughts please.

Glyn

https://www.dropbox.com/sc/2mh4f7vswhi5f2o/AACIJNEbrzVLZExrW7fNVF9Ea

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My thinnest spare shim is 84 thou so I cannot help but if you shift your shims around (e.g. the move 78's to position of the 80's) you hopefully will have clearances to measure without repeated shimming and will only need to find a shim thinner than the 70 thou one.

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Had same problem when rebuilt mine.

At the end it has been a nightmare to shim the valve due to new valves and seats, your best option is to buy a full set of new tappets....they are designed with thinner inner pad where the shim sits on, so you will gain all the spaces to measure the shims required.

Other option, I will send you my set of spares shims for the Lotus engine, I have nearly 250 of them but they are heavy and the postage will be expensive.

 

Giorgio

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Have you measured the gaps with no shims at all?

Suppose you have a gap of 60 thou with no shim at all and you are aiming for a 6 thou gap then buy a 54 shim that should then ensure the correct gap.

Not trying to teach grandma to suck eggs but obviously inlets and exhausts need different gaps Once you know the ballpark area you can buy a selection of shims either side to help with the best fit

John

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Hi John

The design of the valve assembly means that shims must be fitted. If left out the bucket would foul on the retainer and not act on the valve.

Had same problem when rebuilt mine.

At the end it has been a nightmare to shim the valve due to new valves and seats, your best option is to buy a full set of new tappets....they are designed with thinner inner pad where the shim sits on, so you will gain all the spaces to measure the shims required.

Other option, I will send you my set of spares shims for the Lotus engine, I have nearly 250 of them but they are heavy and the postage will be expensive.

Giorgio

Hi Giorgio

Yes I now understand whst you mean.

If I go too much thinner on the shims the bucket will act on the top retainer. To get the clearance I think that I may need to fo what you suggest. Where did you buy them?

Unless there are any other alternatives?

Maybe cams could be a way forward?

Glyn

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  • 3 weeks later...

I don't believe you need to resort to new tappets. Your thinnest shim is 70 thou and you can go down to 60 thou.

Hi Derek, stupid me, but on re-measuring the shims, it was 80 thou and not 70!

Found some time on Monday and had a play around, managing to get a measurable clearance on all valves except one. Ordered a couple of small shime from QED, which should hopefully arrive today.

The set of shims I've just leant out go down to 75 thou' but I think I do have some down a bit further as part of a Hesketh set.

Thanks Andy for the offer. I've ordeed a couple of shims and hopefully will be able to order what i will now need.

Glyn

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Thanks for your help so far. I'm almost there and I do hope that my questions are helpful to others!

So, just a quick update of where I'm at:

Head been reworked, re-assembled and refitted to block.

Clearances measured (dry with no sealant between the cam towers and head).

The clearance spec is 6 thou +/- 1 thou and 11 thou +/- 1 thou

The Lotus notes, say to add 1/2 of 1 thou to the new shims needed to allow for the sealant.

As feeler blades measure to the nearest thou, am I better am I better to shim towards the smallest clearance or the largest?

Am I correct in assuming that wear of the valves and seates tends to make the clearances smaller?

For example, which is the better choice:

Inlet clearance shimmed to 6 thou as per spec. With the added sealant this would increase the clearance to 6.5 thou (above ideal value)

OR

Inlet clearance shimmed to 5 thou. With added sealance, this would increase the clearance to 5.5 thou (under ideal value)

OR am I just overthinking this!

I really hope this makes sense to someone...

Glyn

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Forget about "sealant". Much better to use the "zero thickness" stuff that S&J sell...then you need make no allowance for it. Also, when measuring valve clearances after the seats have been recut or valves ground, you don't need "proper" shims. Just something round and flat and with a measurable thickness.....like washers. When I did mine I used washers on all the valves...making sure they were flat...and then measured everything and did the sums. Worked a treat.

Also, the final check to do is a "go/no go" check. If the gap is given as 6 +/- 1...then it must lie between 5 and 7. So a 5 thou feeler gauge must fit through the gap, and a 7 thou gauge won't. If that's the case, then all is well. Pretty near impossible to measure the true gap using one feeler gauge, as it becomes a matter of ...er.....feel!! Always better to check that the quoted thinnest one goes through and the thickest one doesn't...gets rid of the guesswork.

Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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Thanks again.

So been at the garage...

On exhaust number 4 with a shim of 61 thou I measured a clearance of just 6 thou. I need another 5 thou. I can get 1 thou from a 60 thou shim.

Where am I doing to get another 4 thou from?

What are the options except from pulling the head again and replacing the valve seat.

Getting really fed up of this!

Thanks in advance.

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I checked the shims delivered today. The 60 thou came in at 61.

I've mic'd the pad to cam face on all exhaust followers which are the same 223 thou. Can I go thinner than a 60 thou shim by getting one ground down or will it affect mechanical clearances within the valve train?

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At  223 thou your tappets are 1 thou smaller than mine so probably within OE tolerances.

 

If you ground down your shim you would have to get it hardened again as I think they are only case hardened.

 

You can get shims thinner than 60 thou but I'm not sure how much thinner you can go than 60 thou before the valve spring retainer fouls on the inside of the tappet.

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At 223 thou your tappets are 1 thou smaller than mine so probably within OE tolerances.

If you ground down your shim you would have to get it hardened again as I think they are only case hardened.

You can get shims thinner than 60 thou but I'm not sure how much thinner you can go than 60 thou before the valve spring retainer fouls on the inside of the tappet.

Georgio earlier in the thread mentions some followers which had thinner pads. If thinner pads work then I would assume thinner shims would too up until they just aren't stiff enough.

Anyone know if the shims are just case hardened or not?

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Travis I'm not familiar with your terms. Do you mean the collets which sit in the valve stem groove? I've not noticed anything peculiar.

 

The valve spring retainers.

P7032105.JPG

 

Sorry, re reading above, looks like you have the same old valves, but the seats were re-cut. 

So your only options would be to have the valve stem(s) ground down, or to replace your tappets with the later thinner version, which is what I have. 

 

All my exhaust tappets were starting to crack, so I got the new steel tappets from JAE with a .200" pad, and then had to get measurements to order new shims.   I ended up making a set of taller cast iron fake shims to get measurements, and then ordered the new shims in the .100-.128" range.

 

Cracks forming in old tappets.

IMG_2587.jpg

 

New tappet, light weight steel, with thinner .200" pad

IMG_2649.JPG

Travis

Vulcan Grey 89SE

My Lotus Photo and Projects Album

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Take 2thou off either side with wet & dry on plate glass.  It will be absolutely fine (assuming follower doesn't then foul the spring retainer).   As a tip for next time!  - always  shim the valves before fitting the head.   You could probably also safely remove 4thou from the valve stem but that would not be a diy option.    

Edited by 910Esprit
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  • 2 weeks later...

Take 2thou off either side with wet & dry on plate glass. It will be absolutely fine (assuming follower doesn't then foul the spring retainer). As a tip for next time! - always shim the valves before fitting the head. You could probably also safely remove 4thou from the valve stem but that would not be a diy option.

Yippee. ..

Finished the clearances this morning.

There are so many variables...

Feeler blades and their use and feel

Micrometers and calibration

Shims from different suppliers

I reduced the 60 thou shim using 400 grit wet and dry, and if doing this again, would do this on all shims that are withing a few thou.

You can order shims but in my experience it's hit and miss I'd you receive what you want.

Thank you to those who helped me with this.

Anyway next job...

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