Canada1

Hello Rob,

What part of Canada did your friend move to?

Desmodromic was used by a few teams in F1 - I think Ferrari in the early 90's?
I think only Ducati made Desmo valvetrains for the general public.


I have looked at the Kent and Piper catalogs, and the recommended single and dual valve springs for the cvh seem very weak - in fact lower spring presures than the Ford single.
No wonder NMS and others recommend new Ford springs.

It would be very interesting for someone - maybe a shop - NMS or Jano, to measure the different recommended spring pressures - Kent single and double, Piper single and double, and Newman single and doubles and Ford standard springs.
The installed (closed) pressure, and the pressure at .400" lift.

A proper valvespring comparo would be uber usefull!

I will start:

std Ford (Canada) cvh spring - closed 90 lbs, open (0.400") 200 lbs.


I always measure valve spring pressures (closed and open) for my engine builds.

Did it with the Cosworth 3 liter 4 cyl engines I built, the 2 Porche 6's I built, and both big block ford V8's I assembled. This is one detail you should not overlook.

Cheers

Rob_DOHC

iTrader: (4)

If you were driving notmally a few mins later (and not at high rpm) i suspect you timing belt skipped a tooth or three lol, was it only the exhuast valves that hit the pistons?

Rob_DOHC

iTrader: (4)

Hi Perry, he moved just out side of Toronto.

Im not sure any Jano or NMS would have the equipment to measure spring pressure....?

I guess you could measure its length then load it with a know mass untill you are @ .400" but it wouldn't be too accurate.

Rob,

essexRSTSouthend

Yes mate.was driving normally after woulds,as i came off the main road up the slip road,was rough as hell ( 3 cylinders ).No compression on all 4 cylinders,found to be all four exhaust valves bent.Inlets were fine.dents on the pistons just exhaust side.was very strange.I thought exactly that rob,belt slip or valve float.The worst thing was it was set up the day before it happend!

iansoutham

I had exactly the same problem with an XR3i.

Brand new top-end rebuild using a Kent Cams CVH22. Used their cam, tappets, springs, the whole lot. Steel adjustable vernier pulley set at 0 degrees until run in. Car did 100 miles or so, then, while down-shifting from 3rd to 2nd at about 3000rpm max under light throttle, it just started sounding terrible. Pulled the car over to the side of the road and it cut out. Restarted again using a lot of throttle and constant revs. Drove it home, let it cool down and there was no compression on any cylinders.

Took the top off and 7 out of 8 valves had hit the pistons. Timing belt was timed up perfectly, nothing had moved or slipped. Put 8 new valves in (no point messing around with the 1 remaining good one), "pocketed" the pistons slightly with an angle grinder and put it back together with some normal Ford valve springs and another new belt and it ran fine ever after. Redline was somewhere near 7k as well afterwards and it used to find it often.

The only thing I can put it down to was one of the valve springs "binding" slightly for a second, causing the valve to stay open slightly longer than it should, which would allow it to hit the piston. This then had a domino-effect on the others.

Canada1

Hello Iansoutham,

Wow!
Certainly severe valve float. When valve springs are too light the valves literaly are not in control of the camshaft any longer. Kissing pistons is what happens.

I am still at a loss as to why UK camshaft maufactures recomend valvesprings with too
little pressure. The Ford cvh has a very heavy valvetrain - lifters and steel rocker arms;
The 2.0 Pinto does not have lifters and heavy rocker arms, yet one still runs 80 lbs closed pressure on those engines for 7000 rpm use.

Versus_Creations

iTrader: (1)

I have access to equipment that measures any pressures you would want to know. My good friend and engineer has millions of £ worth of equipment. Their main line of work is for keloggs, tate and lyle, sainsburys to name a few of their clients. He basicly makes all of their tools and machines. So measuring spring pressure is one of the simple things that can be done along with more involved testing like air flow or flow rates etc etc.

You must remember that we are in the heart of the Engineering areas in Essex with everything you could ever want and need within a 20 mile radius.

If i cant do what i want in house then it will be done on the best available equipment.

Versus_Creations

iTrader: (1)

Thats funny as your XR3i can only ever rev to 6200 RPM. How did you manage the other 800rpm.

Rob_DOHC

iTrader: (4)

Hairy muff mate, my point wasn't a dig, just stating that you wouldn't have one in house.

Valve springs are fairly unique, in their size vs spring rate, the equipment used to measure them will probably be pretty unique too, any company that makes springs (die springs especially) should have a suitable piece, especially any firm who makes valve springs!

Rob,

iansoutham

When you work it out, come back and see me

It was a very simple mod back in the day and allowed them to run until either they valve-bounced or ran out of fuelling.

Canada1

Hello Jano,

I own a valvespring test gauge also, but do not have access to the different valvesprings that Newmans, Kent and Piper recommend for cvh use.

There are several different types of testers. Some are more costly, and of course higher quality for a shop to use. I use the type that can be used in a shop vise.

Kent Springs: VS22 and VS42
Piper Springs: VSSCVH and VDSCVH2
Newmans: single and double (not sure if there are part numbers?)
The catalogs do not give close and open pressures for any of these springs.
Seated or closed pressures are important for setting up valve springs (one can shim the spring to increase pressure to where the builder wants).
Open pressure will depend on camshaft valve lift and the specific spring rate of the spring.
Closed pressures have very little impact on camshaft life - but have a huge impact on valve float rpm.

In any case you must measure installed valve spring height with any brand spring you use. You could run into valve spring bind or too low spring presures - with anyones valve spring.


This is the type I use.

Rob_DOHC

iTrader: (4)

These are the type i have seen before,



But again, i guess you get what you pay for.

Canada1

Hello Rob,

The type you show is a high quality tester.
For shop use at an engine builder - to be used 1000's of times.

The lower cost ones work well for the average home builder.

One can calibrate the smaller ones - they are actually quite good.

Cheers

Rob_DOHC

iTrader: (4)

Good stuff, worth knowing!

Maybe i'll get one when i change my cam,

Im interested in Cam design, do you have any good reference material Perry?

Rob,

rstdave

iTrader: (3)

I'd already mentioned i HAD measured the springs but no one took any notice lol
The newman's were nowhere near what they were supposed to be, and the ford ones were what the newmans were supposed to be hence why they work.....simple

Rob_DOHC

iTrader: (4)

Good man, didn't realise you had actually measured them!

Canada1

Hello rstdave,

Tell us your measured results!
What were the closed and open pressures of the Newman spring vs. the Ford springs.
Also what did you use as the closed height? 37mm (1.46")?

That info would explain for everyone.

Cheers

Versus_Creations

iTrader: (1)

Only just noticed this was aimed at me pal.

Its nothing new, changing an electrical component in the black fueling ecu will allow a further 500rpm higher rev limit. But still wont be any more than 6700rpm as per the S1 ECU.

Which is still off what you say.

Rob_DOHC

iTrader: (4)

You can remove the rev limit all together mate.

iansoutham

Ah, I see where we are getting mixed-wires.....

You are talking S1, I am talking XR3i n/a.

dbanbery

Don't know whether anyone has mentioned a few reasons why people are getting valve bounce with uprated valve springs vs the standard ford ones but i thought i'd have a go with my two penneth and join in from what i sort of know.

thickness of the spring wire dictates the preload and the lift. uprated valve springs made out of thinner steel give the correct lift but dont generate the right preload. the higher the preload, the faster the valve closes - if the preload isnt high enough the valve can leave the contact surface of the cam lobe and cause issues. did somebody mention bending valves?

hence the use of double valve springs

the other issue stated below concerns double valve springs being fitted to the cvh. they tend to go coilbound unless the inner spring is located properly.

http://www.pumaracing.co.uk/CVH.htm

most of my knowledge is from this above.

personally i will be modifying my NA EFI CVH but am undecided on what cam to go for. i want to go for something like a CVH33 but am unsure of what springs to go for due to the issues illustrated by people on this thread and in the article above.

interesting point in this article about the exhaust valves on a CVH... lol

fiesta23

iTrader: (1)

i just purchased a newman cam kit from sitech racing. in the kit you get a billet metal clamp to hold the lifters for adjusting them. also i was recommended to stick with the ford valve springs.

Simon was very helpful aswell when i was there.

Craig