Mi16 Springs

[mmt 15]

Hi

I'm looking for some stiffer/tougher valve springs for my mi16.

 

Do anybody have experience with cat cams PAC-S10011 springs? How much of an improvement are they?

 

I do not want doubble springs just single springs that will cope better with High revs. Can you reccommend some springs and also reccommend where to buy them.

 

 

Thanks

[JeffR 51]

I've got those springs in my big valve Mi16 head thet PeterT rebuilt for me. A huge improvement over worn out originals! Good for 8000+rpm.

[JeffR 51]

Came from DES Developments I believe but I don't think they're in business any more.

[mmt 15]

Thanks.

 

Are they a straight fit or do I need to modify anything?

[petert 586]

You'll need thicker shims to get the seat pressure correct.

[mmt 15]

Ok. Thanks.

 

How thick do the shims need to be? Do they come together with the springs or do I need to find Them seperately?

 

What would happen if I used the new springs together with the old shims?

 

Thanks again

[mmt 15]

Will they not work with the original shims?

[welshpug 1,657]

There are no shims originally, only a spring seat.

 

You set the spring pressures by varying the shim thickness under the lower spring seat.

[mmt 15]

Thanks. There's shims under the original springs now. Gues someone before me played with spring pressure.

Will I be ok if i use the cat cam springs and the shims I found in the head ? Or should I loose the shims instead?

 

Thanks again.

[welshpug 1,657]

They wont be shims, there is a lower spring seat, shims are thin.

 

 

Stick a picture up.

[mmt 15]

This is what I found under the springs. About 0.5 mm thick.

[mmt 15]

The "std. Springs" in my engine are 47 mm High and the Catcsms are 44mm. Is it that "gap" that requires to be shimmed?

 

Should the shims be 3 mm or more or less?

Edited February 13, 2014 by mmt

[welshpug 1,657]

no, its the spring seat pressures that need to be checked and corrected, the new springs are shorter because they are stiffer.

[mmt 15]

no, its the spring seat pressures that need to be checked and corrected, the new springs are shorter because they are stiffer.

What does that mean ? And how do I do it ?

[petert 586]

In a standard head there is one 0.5mm shim under each spring. This gives an installed seat pressure of approx 80lbs. If you put the new shorter springs in with a standard shim you will have significantly less seat pressure. The valves may not seal properly and it won't rev. It may not even idle properly. It has been my experience that you need significantly more than 0.5mm with those springs. I'm not going to tell you how much, as this varies with valve length and how much the valve seat has been cut. Measuring installed spring height is not a difficult process if you have the correct tools. I suggest you take your head to a head shop who has the gear to set them up properly.

 

Also, you can't just add 0.5mm shims together for a thicker shim, as the heat transfer won't occur properly between the multiple faces and you'll over heat the springs.

Edited February 13, 2014 by petert

[mmt 15]

Thanks Peter.

 

Catcams sells a set of shims together with the shorter springs. How are the shims adjusted? Would I damage anyting if the shims are too Big and therefore creating more than the 80 lbs pressure?

[welshpug 1,657]

You risk going coilbound.

[petert 586]

You need to measure the vertical height of the space where the spring & shim sit. ie dry assembly with no spring or shim. Then you put the spring in a spring tester to establish what height equals 80lbs. Then compare the required spring height with the height from the dry assembly. Add shim as required. I buy mine from here:

 

http://www.precisionshims.com.au/

 

A typical order for 16 springs might be

 

3 off 1.00mm

7 off 1.25

4 off 0.75

2 off 1.50 and so on.

 

As I said earlier, take it to a head shop or engine builder. Too much seat pressure wastes hp and may lead to spring bind when the valve is fully open.

[B1ack_Mi16 67]

Will it be very evident if one lacks sufficient seat pressure?

 

I'm quite sure I just put one single lower spring seat washer under each of the springs in the 2.3 engine, however it revs. 8000rpms just fine.

[petert 586]

The less mass you have the less pressure you need to control it. So fitting lighter solid lifters probably helped. I can't imagine standard hydraulic lifters with stuff all seat pressure is going to work very well. And now you've been made aware of the problem would you go ahead and do it?

[B1ack_Mi16 67]

Of course for a new build one should check it and get it correct.

[mmt 15]

I will take away the 0.5 washer and install a 2mm shim instead. This must work it is not a Moon rocket I am building. It's not going to rev more than 6500-7000.

Was it the 0.5 std washer you installed or an other size? Remember?