Shim Under Valve Spring Seat

[RSOHC]

I am in the process of changing the valve springs in my 2.7 liter 911S engine and have not found any shims under my valve spring seats. Should there be a shim under the valve spring seat?

Lauran

[john walker's workshop]

!-5 is in the normal range. Were the springs aftermarket beefy ones?

[Zuffenwerker]

930-105-461-00
Here’s your part #. If the heads are still on the engine it’d be hard to check spring installed height. If your on the bench and putting in stock springs your gonna need to buy a whole bunch

[dannobee]

Check again with a magnet. They might be there, but stuck due to oil making them stick to the head.

[RSOHC]

How do I measure the spring height?

[RSOHC]

The springs are stock. The engine is in the car.

[Classic 911]

Following


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[RSOHC]

According 1975 Model 911S 2.7 Technical specifications, my engine should have installation lengths of valve springs of 35mm +/-0 0.3mm for the intake and 35.5mm +/- 0.3mm for the exhaust.

[RSOHC]

Where can I find a valve spring micrometer that can read values of 1.366 inches and 1.409 inches?

[Zuffenwerker]

Just use a digital caliper. Measure the thinnest (outside) shoulder if the retainer and zero the caliper. The. Install a weak spring with shim pack and spring seat, keepers, etc. measure from the top of the retainer to the spring seat. That is your spring installed height

[RSOHC]

Where can I source the weak spring?

[ed mayo]

Any Ace hardware store

[Neil Harvey]

If I can add some info for you.

You are "measuring/calculating" the seat and nose spring pressures. Porsche realized most would not have the equipment to measure the actual pressures so they give an installed height that is an approx to the required pressures. Someone here has given the installed heights. Shims are available to obtain those heights. I cannot remember the thicknesses available, I think 0.010" and 0.020". You can buy Arbor shims as thin as 0.002" if you needed. But the shims from Porsche are what are considered close enough. No two new springs will have the same pressures v height.

Some important info here, you can expect the retainer heights to be between 1.300" and maybe as high as 1.500''. If the seats have been cut low, this height will be more towards 1.500".

If I was in the "bush", here is how I would do this. I would take a spring base and retainer to my local hardware store and buy a piece of PVC pipe that had an ID and OD that would fit the two pieces. I would buy a cheap drill index that went as high as 1/2" as well. Go home and cut the PVC to 1.250" as accurate as you can. Maybe run both end across some sand paper to true up the faces.

Fit this "spacer" between the base and retainer on each valve, to measure, with the locks fitted as well. Bottom out the retainer against the spacer with some slight force to seat the locks. Now use the drill bits as gauges between the spacer and the bottom of the retainer where the outer spring seats. The drill bit that fits snuggly is the size that gets added to 1.250". Covert to metric or convert the installed height required to imperial numbers and add shims to obtain these required installed heights.

Maybe this is helpful. You do what you have to when its required.

[dannobee]

The Porsche special tool is P228, although the marks were never intended to be used in place of a "real" valve spring installed height micrometer. They would get you in the ball park if you lacked the more accurate tool. If you're doing this whole affair in the car, you'll likely need a borescope tool or mirrors to read the installed height.

When the SC's had the bad batch of valve springs in the 80's, we changed a lot of them in the car and it was hard enough to change the springs, much less adjusting the spring heights. Most of us would just replace the springs and not alter the number of shims. But remember, when under warranty, they weren't 40+ years old and not already been apart and fiddled with a few times.

[RSOHC]

I have ordered a telescoping bore gage. I can use the gage to measure the distance between the retainer and the seat. I can have the inner spring of my spring set in place when doing this measurement. The stack would consist of retainer with keepers in place on top, inner spring in the middle, and valve seat on the bottom.

Any shims added below the valve retainer would decrease the installed height.

The part number of the shim from Porsche is 930-105-461-00. The thickness of the shim is 0.50mm. This is the only shim thickness produced by Porsche for a 911.

[RSOHC]

The P228 tool is currently not available from Pelican Parts. I will call SIR Tools on Monday and ask if they have this tool in stock.

[RSOHC]

The snap gage set I received is too large for one end of the probe to be placed between (1) the outer edge of the seat that is the contact point for the larger valve spring and the smaller valve spring and the other end of the probe to be placed between (2) the lip of the retainer that is the contact point for the larger valve spring and the smaller valve spring.

[RSOHC]

As some background, my engine has had a persistent engine miss.
When I decided to pull and then reinstall the ignition wire off each spark plug one at a time to see how the rpm of the engine changed.
For cylinder 1 though 5 the rpm decreased from 666 rpm 630 rpm when the spark plug wire was removed and went back to 666 rpm when the wire was reinstalled.
However, for cylinder number 6 the rpm increased from 666 rpm to 766 rpm when the spark plug was removed and went back to 666 rpm when the wire was reinstalled.

[RSOHC]

Ass additional back ground, I have tested all my new springs using 42 mm for seat pressure for both intake and exhaust, 30.5 mm for intake full pressure, and 31.5 mm for exhaust full pressure.

The target value for the seat pressure is 44 psi +/- 5%.
The target value for the intake full pressure is 176.5 psi +/- 5%.
The target value for the exhaust full pressure is 165.3 psi +/- 5%.

The seat pressure values for the new spring range from "in Spec to 6 psi above the high range" for the spring being acceptable.

The intake full pressures for both intake and exhaust applications are within the range for the spring being acceptable.

[RSOHC]

I have ordered from Summit Racing a "Proform Valve Check Spring 66793" which has a height of 2.000 inches and a spring diameter of 0.875 inches.