Getting ahead of myself, but: Cam timing?

911hillclimber · Post by **911hillclimber** » Sun Nov 28, 2021 12:48 pm

Soon be putting the Kent GE60 cams into my 3.2 which will be twin spark (if that has any bearing on this question).

I've timed stock cams on 3 911 engines, all ok, but they were all stock (911E and 2 x 3.2).

I am asking how to time the GE60's.
Do I follow the same factory sequence for stock cams or should I do something else, ie take it to Greatworth Classics etc??

Kent themselves will only say 'discuss with your engine builder' so asking for advice please.

PeterK · Post by **PeterK** » Sun Nov 28, 2021 1:39 pm

AFAIK, the sequence is exactly the same. All that may vary is the value you choose - 1.1, 1.4 or whatever

Kneeslider · Post by **Kneeslider** » Sun Nov 28, 2021 1:48 pm

Thats a very good question! And an important one.

I think its also a bit like the endless "What jetting is correct for my engine" questions...

Its probably something that you can play with endlessly to try and get where you want to be. If it were me, I would start with the inlet cam centerlines somewhere about where the stock ones are, and then its a question of how much time you want to spend on a dyno dialing them back and forth. I've never played with 911 engines, but thats what I used to do with SOHC 2v Ducati engines.

MikeB · Post by **MikeB** » Sun Nov 28, 2021 1:51 pm

Graham, it would just be the same procedure, but obviously using the different lift value (5.00 mm) at TDC for Nrs 1 and 4 cylinders.

911hillclimber · Post by **911hillclimber** » Sun Nov 28, 2021 2:28 pm

Thank you all.
I suspected to go stock alignment but adjust for the lift of the GE60.
There is/was folklore about one end of the timing envelope for torque, other for power. Bob Watson held some respect for this but not sure if it really matters.

On this 3.2 I've gone for middle position both rebuilds.(and had 261 bhp)

hot66 · Post by **hot66** » Sun Nov 28, 2021 5:03 pm

Mike B always sets the timing to allow for it to change as the new chains bed in and stretch .

Kent cams

https://www.kentcams.com/part/GE60?manu ... engine=302

https://forums.pelicanparts.com/911-eng ... -spec.html

911hillclimber · Post by **911hillclimber** » Sun Nov 28, 2021 5:30 pm

Interesting James.
This engine in 5 years has done about 250 miles, not sure how much the chains may have stretched over that time though.
My general guide will be the Dempsey book for the rebuild.

Might treat myself to a digital DTI gauge as I'm getting too old now!

Wish those pistons and rods would appear.

andytat · Post by **andytat** » Mon Nov 29, 2021 2:31 pm

From the Kent spec sheet it looks like you set the cam timing to 5.0mm intake valve open at TDC
on overlap. I would definitely check the valve to piston clearance when done just to be safe.

Andy

911hillclimber · Post by **911hillclimber** » Mon Nov 29, 2021 3:30 pm

Thanks Andy, that is the plan, but late Dec as no sign of them yet.

What would be a reasonable clearance, 2.5mm?

Gary71 · Post by **Gary71** » Mon Nov 29, 2021 3:38 pm

Not sure about the clearance, but other than machining those new pistons you haven’t got yet and losing compression ratio how do you fix it?

I’d certainly check the clearance +/- 10deg from where you are planning to set the timing to allow for drift and/or you wanting to change the cam timing on a dyno.

911hillclimber · Post by **911hillclimber** » Mon Nov 29, 2021 5:36 pm

I doubt this engine will see a dyno, though I have looked the other day at Neil B's set-up.
I imagine the cost to be 'big'. Only worth it if you can delete the need for a rolling road/map.

I plan to dry build one side to check piston to head and piston to valves and really don't expect to have to touch the pistons, BUT to be sure of this I need to know what typical clearances are.

There is a cracking series on youtube from a guy in the USA rebuilding his 2.2S and he has 2.5mm clear of the piston sides to head chamber, but he was fitting S cams to JE low compression pistons (9.5:1) as he can only get 92 ron in his state.

He used modelling clay (could be plasticine?) but I've seen a DTI gauge used instead and super light valve springs (have those).

For the 911 engine hand tight cylinders 1 and 3, piston on #1, cam carrier on the heads and cam in, no chains
You set #1 to tdc and turn the cam to set the valve clearance to 0.4mm on the heel.
You then turn the cam gently to peak of the inlet lobe, zero the dti and then press the valve down by finger so the valve head touches the piston. That is the gap you have.
Do the same for exhaust.

People say 80 thou for inlet, 100 thou for exhaust, ie 2mm and 2.5mm min

I'm down at Greatworth Classics tomorrow so will ask Angus.

PeterK · Post by **PeterK** » Mon Nov 29, 2021 5:48 pm

FWIW, Wossner recommend 1.5 inlet & 2.0 exhaust valve to piston minimum clearances

911hillclimber · Post by **911hillclimber** » Mon Nov 29, 2021 5:52 pm

Worth a lot Peter, thank you. IIRC you went through all this on your thread?
I value your opinion anytime.

More people checking my moves the better.

PeterK · Post by **PeterK** » Mon Nov 29, 2021 6:36 pm

MikeB · Post by **MikeB** » Tue Nov 30, 2021 11:41 am

An easy way to check the clearance to the valve is by screwing in the tappets, they are a 1.0mm pitch, so bring the car up to TDC and see how many turns you get before valve touches piston, or you reach the point where you know you have enough clearance

DDK - Die Deutschen Klassiker