Valve Clearance on a 2.0S

914obsession · 02:14 PM

I am rebuilding my 914-6 motor and doing a few upgrades. Among them are a set of 2.0S pistons and cylinders and E cams. I was told that the 914-6 heads were the same heads used in the 1970 911T cars. After finishing assembly of the short block yesterday I tried to measure the valve clearance. The Bruce Anderson book says that you need a minimum of 2mm clearance between the piston and intake valve at TDC. I have much more than 2mm clearance. Is there an issue using the 1970 style heads with the 1968 911 S pistons and cylinders. The 914-6 heads were the same as the 1970 and later heads in all respects except for the fact that they accommodated the early style cylander gaskets. Also, does anyone know what the spacing is supposed to be on the hydrostops for the chain tensioners? I thought it was 1mm. Any advice would be appreciated.

Thanks!

kenikh · 02-10-2008, 04:12 PM

My recollection of the facts are different than yours. 914-6 heads, by my recollection are an early "deep dome" head, which is identical to 1969 'T' heads, not 1970. If your heads were the later shallow dome heads, the issue would be valve angle. The lower lift of the E cam might afford you enough clearance, but in all likliehood, you would need to clearance the pistons for different valve pockets to accomodate the shallower valve angle. Post some photos; I can tell by looking at the combustion chambers which heads you have.

one914racer · 02-10-2008, 04:27 PM

pictures of dan.s engine

914obsession · 02-10-2008, 04:56 PM

There seems to be too much clearance between the pistons and valves. At TDC I tightened the valve adjustment screw (counting started once the valve adjustment screw was actually touching the intake valve) in as many rotations as I could, 7 full rotations without the valve hitting the cylinder. That should mean that I have at least 7mm of valve clearance. Somebody had once posted a thread stating that the 914-6 heads where actually identical to the 70 and later heads except for the cylinder gasket groove. Does anyone know what the valve clearance for the intake valve should be at TDC for a stock 2.0S?

Eagledriver · 02-10-2008, 06:55 PM

It's not clear from you description that you are talking about the valve to piston clearance at TDC on the INTAKE stroke. This is not the same as the clearance with no valve lift at TDC on the compression stroke. This check is done in conjunction with the cam timing operation. You set the cams with the appropriate lift setting at TDC on the overlap of exhaust to intake stroke. Then you check to see how much valve to piston clearance you have in the vicinity of that TDC. The closest approach for the exhaust valve is around 7 degrees BTDC and the closest approach of the intake valve is around 7 degrees ATDC.

-Andy

kenikh · 02-10-2008, 07:33 PM

Those are almost assuredly deep dome heads and those pistons don't look like 'S'; the look like 906 (w/ 10.3:1 CR)! 1-69 cast date confirms that, not to mention the massive gap between valve margins.

914obsession · 02-10-2008, 08:10 PM

I believe I measured the intake valve to piston clearance at TDC and at a bit past TDC. Is there a measurement that I should be close to assuming the pistons I have are 2.0S? I'm pretty sure I saw a similar set of pistons for sale on ebay advertised as 2.0 "S" and they looked identical to mine. I'll see if I can find a picture of one of the pistons to post. If it is a 906 piston is it possible that I would have to use different length rods or a different crank? The pistons were mahle's and did have the "S" piston cer clips in them. I'll try to get a photo posted. So the heads are definitely the earlier style? I know that the date stamp is 69 but I was pretty sure that I read that the factory used later style heads for the 2.0 six engines. If these are the early style heads, what sort of horsepower reduction am I looking at? Everything in the engine was balanced by at a machine shop, the oil bypass modification was made, the case was bow-tailed and the cylinders moored. I have a set of headers and webers with higher PMO intake manifolds.

kenikh · 02-10-2008, 08:19 PM

Quote:

Originally Posted by 914obsession

I believe I measured the intake valve to piston clearance at TDC and at a bit past TDC. Is there a measurement that I should be close to assuming the pistons I have are 2.0S? I'm pretty sure I saw a similar set of pistons for sale on ebay advertised as 2.0 "S" and they looked identical to mine. I'll see if I can find a picture of one of the pistons to post. If it is a 906 piston is it possible that I would have to use different length rods or a different crank? The pistons were mahle's and did have the "S" piston cer clips in them. I'll try to get a photo posted. So the heads are definitely the earlier style? I know that the date stamp is 69 but I was pretty sure that I read that the factory used later style heads for the 2.0 six engines. If these are the early style heads, what sort of horsepower reduction am I looking at? Everything in the engine was balanced by at a machine shop, the oil bypass modification was made, the case was bow-tailed and the cylinders moored. I have a set of headers and webers with higher PMO intake manifolds.

There is no loss in power with earlier heads. Thats said, they do better with twin plugs. If those are 906 pistons, you will need twin plugs anyway (not optional) due to CR. For reference:

906:

2 liter 'S':

Now do you see what I mean?

914obsession · 02-10-2008, 08:33 PM

I see exactly what you're talking about. My pistons are definitely like the 906 pistons. Are stock rod lengths and a 66 mm crank correct for these pistons? My cylinders are the same as the standard biral 2.0 E/S cylinders. Here's a few photos.

kenikh · 02-10-2008, 08:36 PM

See comments inline...

Quote:

Originally Posted by 914obsession

I see exactly what you're talking about. My pistons are definitely like the 906 pistons. Are stock rod lengths and a 66 mm crank correct for these pistons? Yes My cylinders are the same as the standard biral 2.0 E/S cylinders. Sort of. You can use Biral cylinders and yours look like Biral, but these originally came in Cromal cylinders. One other twist: these pistons usually came in 81mm diameter, but 80mm was not uncommon

914obsession · 02-10-2008, 08:39 PM

How rare are these 906 pistons? if I did run twin plug and this setup what sort of horsepower would this engine put out?

kenikh · 02-10-2008, 08:50 PM

Quote:

Originally Posted by 914obsession

How rare are these 906 pistons? if I did run twin plug and this setup what sort of horsepower would this engine put out?

Not super rare; can still be bought new from Mahle, I believe. Still, not super common either. How much power? I just reread your first post and would definitely NOT recommend using E cams. With their lack of valve overlap, you are going to get a dynamic CR (to this point we were talking about static CR) way too high for a street motor, even with twin plugs on street gas. That said, with a higher performance cam (S or bigger), it would be no problem. All things being equal, you can expect about ~5% more power with 10.3:1 vs. 9.8:1 pistons, with significantly better throttle response on the higher CR.