How to use valve spring platform shims

[holywood3645]

Hi all, I bought some head rebuild parts for my Lotus twin-cam from QED. (Springs Q55, Valves, Q420 Cams, Cotters, spring platforms etc) for a top end rebuild. I asked QED to include and other parts I may need for a top end rebuild. QED included some Valve Spring Platform Shims that i have no idea how to use.

I believe these are inserted under the platform, However I have no idea the theory, or practical use.


Has anyone used these? How are they supposed to work??.help

Thanks

James

[email protected]

[Dag-Henning]

James, they will enable you to obtain the correct fitted length of the new springs , in relation to your valveseat height and valve length. Rohan is the "oracle" here, and may have som input for you if you do some measurments on your head.

Dag

[Foxie]

Hi James, Happy New Year !

I have a QED 420 head, which I recently rebuilt. (Following complaints of smoke at Kirkistown !) The parts you have as supplied by QED should work fine (i.e. no valve bind problems) without the shims, but will encounter valve bounce at a certain rpm. If you are running a standard crankshaft, with a rev limit of ~7K rpm, this may be a good thing, and may save you from over-revving. If you are running a steel engine you may want to raise your rev limit, in which case you can increase the valve bounce limit by increasing spring load, i.e by fitting platform shims. If shims are fitted , you will be getting closer to "valve spring bind" where the springs are compressed to the point where the coils are in contact, and will not compress any more. There is a generally recommended clearance of 0.060" - 0.050" clearance before valve bind. I can recommend the Dave Bean catalogue for more info on this topic. It cost me $6 + $22 shipping from San Andreas CA to Ireland, but it was the best $$ I ever spent. Shouldn't cost so much to ship to you !

If you give QED a call, they will very likely be able to quote you rev limits/shims to be used, they did this for me.

Burtons are also good for advice on this.

Sean

Hi all, I bought some head rebuild parts for my Lotus twin-cam from QED. (Springs Q55, Valves, Q420 Cams, Cotters, spring platforms etc) for a top end rebuild. I asked QED to include and other parts I may need for a top end rebuild. QED included some Valve Spring Platform Shims that i have no idea how to use.

I believe these are inserted under the platform, However I have no idea the theory, or practical use.

Has anyone used these? How are they supposed to work??.help

James

[email protected]

[holywood3645]

Hey Sean, good to hear from you. So basicially your saying to pre-load the valve spring enough to stop valve bounce but not enought to bind, I get that.

Then I have another question, how do you measure the bind clearance in the spring. Thats with the buckets covering the springs, and the cams in place.
James

Next time your in Kirkistown, you need to take a trip over the Holywood Hills and have a drink in my old bar. Its called the Dirty Duck (now) It was the Clipper when I owned it.

[bcmc33]

Sean,

I am a little confused on what you've said.

I have obtained an unused QED 420 head that is destined to go on my engine when the whole thing goes back together over the next few weeks.

The head is shimmed to what I assume is the correct valve clearances on inlet and exhaust cams.
I have not measured them, but again assume inlet to be 0.005"-0.007" and exhaust to be 0.009"-0.011".

I shall make the effort to measure them tomorrow.

What is it I don't understand about your post?

[Foxie]

Hey Sean, good to hear from you. So basicially your saying to pre-load the valve spring enough to stop valve bounce but not enought to bind, I get that.

Then I have another question, how do you measure the bind clearance in the spring. Thats with the buckets covering the springs, and the cams in place.
James

Next time your in Kirkistown, you need to take a trip over the Holywood Hills and have a drink in my old bar. Its called the Dirty Duck (now) It was the Clipper when I owned it.

Yes.

But you must select what the max rpm you want to run. Standard rev limit of ~7K will most likely be what QED have supplied, but check with them. To enable higher revs without valve bounce requires more spring pressure, (with the penalty of some more associated cam/tappet wear). QED can advise on spring load/rev limits. And there are different springs available. To measure spring bind, assemble the head (minimally with one inlet & exhaust valve. Set timing, then, rotating the engine by hand, insert larger and larger feeler gauges until you feel the engine lock up. This setting minus 0.050" is the maximum PLATFORM shim you can use.

The Dirty Duck is now on my destination list

[Foxie]

Sean,

I am a little confused on what you've said.

I have obtained an unused QED 420 head that is destined to go on my engine when the whole thing goes back together over the next few weeks.

The head is shimmed to what I assume is the correct valve clearances on inlet and exhaust cams.
I have not measured them, but again assume inlet to be 0.005"-0.007" and exhaust to be 0.009"-0.011".

I shall make the effort to measure them tomorrow.

What is it I don't understand about your post?

The standard rev limit for the TC is ~7K, but if you have a steel engine which can rev anything up to 10.5K, QED can supply higher rate springs, with fine adjustment set by shims underneath the valve PLATFORM, at the bottom of the valve spring well. These are not to be confused with the tappet clearance shims on top of the valve stems, which determine the cam clearances. Your 420 head is very probably standard, but check the tappetclearances just to be sure !

I'd say you will be very pleased with the 420's tractability and power. I'm really pleased with mine, which with a steel crank has QED fitted springs and shims to enable 8.5K.

Hope this makes things clearer

[Foxie]

Yes.

To measure spring bind, assemble the head (minimally with one inlet & exhaust valve. Set timing, then, rotating the engine by hand, insert larger and larger feeler gauges until you feel the engine lock up. This setting minus 0.050" is the maximum PLATFORM shim you can use.

On re-reading this, I will correct what I wrote and say you don't need to assemble the head to the engine, just fit one cam at a time (to prevent valve interference) to the head, and rotate it manually, whilst measuring for valve bind.

[bcmc33]

Sean,

If I'd read your post properly I would have understood what you meant. Valve pre-load shims OK.

I think the snow has clearly slowed my brain That's my excuse anyway

[rgh0]

Valves and springs in twinks - my favorite topic

Shims are used to set the spring installed height to the correct value adjusting for tolerances in the rest of the assembly. However to use shims it assumes your valve heights and spring pocket depths are sufficient to shim the spring up to a lesser height to achieve the design value. If you dont have the space then you need longer valves or a different design retainer that achieves a greater spring height on the same valve length.

The QED spring will have a specified installed height that should give a seat pressure of around 75 pounds. It will have a maximum specified lift to coil bind above this height that should have at least around 60 thou clearance with the cam lift you are using. Maximum spring pressure at full lift should be less than 220 lbs in my experience to avouid excessive cam wear.

To set all of this correctly you need to be able to measure the spring installed height. A vernier caliper can be used to measure from the top of the valve to the base of the spring pocket and then by measuring the distance from the top of the valve to to the retainer spring seat you can figure out what spring space you have and what seat and shim thickness you need to achieve the correct spring installed height.

A lot of other complexity can come into this depending on the valve location in the head, valve length, cam base circle, spring pocket depth and bucket thickness but the above is the start. if you cant achieve the right installed spring height with what you have then we can discuss the problem more.

Currently skiing in Europe so my replys may be slow

cheers
Rohan

[Dag-Henning]

- skiing in Europe.... If I am not totally wrong, you have a nice summer now around Melbourne.....But, by all means, we have snow to share if you wish.......
Dag

[rgh0]

43C today in Melbourne --- Minus 6 today at Chamonix. The snow is a lot better in Chamonix
cheers
Rohan