Konstantin

Here my question agaian:
The intake valves have a 1 mm shims. the exhaust valve #1 and #2 has 1 mm BUT #3 and #4 have a 1.5 mm (actually one 1 mm and one 0,5mm)
I will put these valves in another head with reworked seats. (0.7 mm deeper)
I must adjust the valves with springs to the new specs. Porsche use a tool to messure the springs and acordingly use the neccecary shims. I do not have this tool. How you guys use the shims and how to know how many are neccecary? I do not think everbody has this tool.
How others know what is the maximum shims that is alowed to use ?
The height on the valves is 41 mm for intake and 40 mm for exhaust valve. It seems that I need 3 mm shims to corect the spring tension. I have 43,2 mm and I need 40 mm on the exhaust valve.

any ideas?????


Konstantin

Pauerman

It's easy...

Install the shims first under the bottom spring cup followed by the lower spring cup. Then, install your valve (intake or exhaust) and the upper spring retainer with the valve keepers installed on to the valve. Now with a caliper or a ruler with fine increments, pull up evenly on the upper retainer and measure the distance from lower sping cup (on the surface where the spring sits) to the rim on the upper retainer.

This measurement is the installed height of the valve spring.

Add or subtract the necessary shims to get your target measurements of 40mm & 41mm

HTH
Vic

Konstantin

hello
when the spring is installed you cna not see the lower cup.
so how can you messure the distance between the uper retainer and the lower cup?
I messured it WITHOUT the spring installed but it seems to me that I must ad 3.5 mm washers. that seems to much.

Konstantin
(PS My valves are now 0.7 mm deeper in the valve seats)

special tool

Konstantin - you do NOT install the spring to measure the height. Push the valve onto the seat and measure from cup surface to retainer rim with retainers installed.

Konstantin

Hello
I already did that
But the 3.2 mm shims that I need seems to much for me!!!!
common is about 0.5 to 1.5 mm

Konstantin

Pauerman

Be sure you are measuring it correctly - (without spring installed) from the bottom cup surface where the spring sits to the rim of the upper retainer (with keepers intalled). Pull up on the upper retainer and take your meaurement. You must add the required amount of shims to achieve your installed spring height of 40-40.5mm exhaust or 41-41.5mm intake.

3.2mm doesn't seem like a lot of shims. Remember you have a half millimeter to play with. The last head I assembled required shims ranging from 1.5mm to 2.2mm shims under all springs.

Check again to verify your measurement.

Vic

m42racer

If I can add something here. Firstly, measuring the Retainer Height can be done with anything round that fits the Spring Base and top Retainer. If you know that dimension, then with either a Caliper, Dial Indicator or even feeler gauges, measure the gap between this "constant" and the under side of the Retainer. Then add this mesaurement to your "constant". This may make the measuring a little easier. Your doing everything at the top. Remenber, you are measuring the distance of the "outer spring" only.

Now, as for this Installed dimension. The question of what you measured is not uncommon. What you are really measuring is the Spring Force that the Spring exerts when the Valve is on the seat. It has been determined by Porsche when designing the Valve train, that this dimension is easier for the masses to measure, not the force. So they calculated with a Spring Test machine, that the force they wanted on the seat is at 41.0mm or whatever. They also measured that with the spring compressed, ( full Cam Lift), the force is whatever, and the distance to spring coil bind is another and there is some distance between the two for safety.
So you are measuring 3 or more shims. What does that mean. A couple of things. You have probably lowered the seat heights after doing a Valve seat cut, or the springs have sagged some. Doing this work at home is difficuilt, as all you probably can do is the linear measuring. Engine builders will measure the spring force, check the Springs for the rate to see if the springs have sagged, and often will add more shims to compensate. Typically the installed heights will change from the 41.00mm to obtain the required seat force.
Things to check, free length of all your springs, are they straight and how do they feel under hand pressure. All very crude at home, but you probably do not have any other way. Even brand new springs have differences. I would suggest, take your springs to a Engine builder who has a spring tester, and ask him to test all the springs at the known heights.

Pauerman

M42,

The problem I came across is that there are no values for compressed spring load or free length posted in the engine sections of the factory manual. Needless to say, my engine builder thought that the installed spring height dimension was a joke cause you can't tell the real condition of the spring unless you put a load on it.

The last time I asked about these measurements, someone posted that the valve spring info is in a supplement section of the manual. Can anyone confirm this cause I apparently don't have it??

m42racer

The free length I mentioned was a simple check of comparision. Look to see if any are way shorter than others. The open length is the Installed height minus the Gross Cam lift.

As for what the pressures should be, all depends upon the valve train component weights, cam profile and required RPM limit. Valve size, seat width ( 45) all are figured into the required seat pressure. I have been told that typical seat presures for approx 7000RPM, 1-1.5 seat widths, and the usual Valve sizes is around 70lbs Intake and around 75Lbs Exhaust with approx 270-290 open force.

Be sure to check all of your own parts etc, and ask your own engine expert for his opinion. These are only guidelines and typical approx numbers.

Konstantin

hello
the height of the loer spring tapet to spring retainer was 44,3 mm
so I need about 3.3 mm of shims to go to 41 mm.
the springs are ok 58 mm long (as factorys says)
the force is 1200 Newton (NA engines have about 1000 Newton)
you must calculate the total length of a compressed spring otherwise you will get Problems if the spring can not be compressed wehn the cam is full open (either 12 for the intake or 11 mm for the exhaust valve)

Konstantin

Konstantin

hello
check the 944 Turbo 1985 information technik book. It has the infos you need

Konstantin

m42racer

Konstantin,
The pressures you post show the reason why the Turbo has a higher seat pressure. They want the valve on the seat with more force to help in the higher transfer of heat from the Valve, to the seat, to the head to the coolant. Pretty normal stuff. Your measurement of 44.30mm shows you may have cut the seat, the valve face or so difference in the Cylinder head. At least you are checking. As we have discussed, the length is not as important as the force required.

Konstantin

yes I cut the seat and I took some off the valve.
So the length in the spring is longer that's why I must ad some shimm to correct the spring force

Konstantin

m42racer

I posted some incorrect info about the seat force on a stock spring. The seat force is around 110lbs on a stock spring and around 250 - 265 over the nose. More force is required as the stock Cam shakes the valve train very hard, so the Valve train is over sprung to compensate. When using better designed Cams, the seat force can be lowered down to 70 -75 Lbs.