Lotus Elan

Stuck Valve Shim

PostPost by: thehackmechanic » Mon Mar 02, 2020 5:54 pm

(Europa TCS guy who posts twin-cam questions here)

I'm doing my first valve adjustment on my twin-cam after its rebuild 700 miles ago. I got the cams and tappets out without incident, but the shim for #1 exhaust valve is stuck in the spring retaining cup. I've tried a pretty powerful rare earth magnet, and it won't budge. I can't find any posts on this on any of the Lotus sites, but I see posts in the motorcycle world about putting a right-sized socket on the spring retainer and pressing down on it or rapping it gently with a rubber mallet. Can I do that here?

--Rob Siegel
'74 Europa TCS, 20k miles, stored since '79, resurrected in 2019
'73 BMW 3.0CSi
'72 BMW 2002tii, '73 BMW 2002
'72 BMW Bavaria
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PostPost by: gjz30075 » Mon Mar 02, 2020 6:48 pm

I'd be leary of rapping the springs. But if you want to do that, bring that piston to tdc, pull the plug and
shove some small rope in the cumbustion chamber so if the valve does drop, it won't go far, However,
getting a keeper back on is pretty tricky. I'm sure the engines guys here might have seen or used a
spring compressor to be used with the head on.
Try a magnet that is no bigger than the shim, pulling straight up.
Greg Z
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PostPost by: rgh0 » Mon Mar 02, 2020 7:40 pm

Never seen it happen before, normally they lift out with the follower stuck to it by a film of oil. The shim should only be supported at the centre on the valve stem I would try tapping the shim down gently with a punch on one side and the other side should come up so you can then pry it out

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PostPost by: thehackmechanic » Mon Mar 02, 2020 8:29 pm

THANK YOU ROHAN! That worked perfectly. There is a libation of your choice waiting for you on the west side of the Atlantic :^)

--Rob Siegel
'74 Europa TCS, 20k miles, stored since '79, resurrected in 2019
'73 BMW 3.0CSi
'72 BMW 2002tii, '73 BMW 2002
'72 BMW Bavaria
'79 BMW 635CSi
'99 BMW Z3M Coupe
"The Hack Mechanic," six books available on Amazon
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PostPost by: rgh0 » Tue Mar 03, 2020 3:42 am

Hi Rob
Glad it worked - If I get to Boston one day I will take you up on that offer

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PostPost by: Gray » Tue Mar 03, 2020 5:28 am

I've had this happen, tapping the shim on one side worked for me as well. I think it is where there is little clearance between the shim and the retaining cap and the 'hydraulic seal' needs to be broken.
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PostPost by: Esprit2 » Tue Mar 03, 2020 8:15 pm

I've not experienced that problem. But I have found that shims from some vendors are a wee bit larger in outside diameter that OEM-stock. I've had a problem with the shims sharp 90 degree outside edge interfering with the slight corner radius in the spring retainer's 'shim cup'. For me, it resulted in a smaller (tighter) valve clearance than my calculations predicted. It was frustrating until I noticed the interference. After that, I'd grind a radius around the shim's OD, on the side that would go down into the retainer. That solved the flakey clearance problem.

So, why did that one shim stick so firmly? Look for a similar shim OD Vs retainer corner radius interference. I don't know that to be the problem; I'm just throwing out an idea for you to investigate. Try to solve the problem so you don't simply re-assemble it the same way again.

Regards,
Tim Engel
Last edited by Esprit2 on Thu Apr 23, 2020 4:36 pm, edited 1 time in total.
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PostPost by: rgh0 » Thu Mar 05, 2020 12:12 am

Esprit2 wrote:I've not experienced that problem. But I have found that shims from some vendors are a wee bit larger in outside diameter that OEM-stock. I've had a problem with the shims sharp 90 degree outside edge interfering with the slight corner radius in the spring retainer's 'shim cup'. For me, it resulted in a larger valve clearance than my calculations predicted. It was frustrating until I noticed the interference. After that, I'd grind a radius around the shim's OD, on the side that would go down into the retainer. That solved the flakey clearance problem.

So, why did that one shim stick so firmly? Look for a similar shim OD Vs retainer corner radius interference. I don't know that to be the problem; I'm just throwing out an idea for you to investigate. Try to solve the problem so you don't simply re-assemble it the same way again.

Regards,
Tim Engel


Original stock shims all had that corner radius on both sides which I presume was to avoid exactly the problem you have seen. I guess some new makers dont understand the need ! Fortunately I had the opportunity many years ago to buy up a complete set of several hundred original NOS shims in the original packaging at a very very cheap price (4 of each thickness in 1 thou increments from around 70 thou to 140 thou ) plus I had already a stock of over a hundred shims from my days owning Hillman Imps and Saab 99's and Lotus in the 70's and 80's So I have not had to buy any new shims for 25+ years :D

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