901/01 Engine

chris_seven · 02-27-2009, 06:30 AM

Have just obtained a Twin Plug 901/01 motor with a very odd combination of heads.
It has the following fitted:

4 x R901.104.304.05 also marked 8-65

2 x 901.104.304.0R also marked 5-70

all heads are fitted withTwin Plugs but all plugs are 12mm diameter and the original plug holes don't seem to have been welded up!!!

Dizzy is a Marelli S121 with 4 x sets of contact breakers and a three-lobed cam.

The difference in the heads is a bit confusing.

304065 · 02-27-2009, 08:48 AM

Chris, how does the engine RUN?

It has four 2,0, 39/35 valve 1966 model year heads, and two 2,2 heads with larger valves! They have different cylinders and mating surfaces too!

Can't wait to see some pictures of this. I am surprised that engine ever worked.

chris_seven · 02-27-2009, 09:14 AM

Grady,

Valve sizes are all the same as heads have clealry all been modified.

Mating faces have also been machined and ports are nominally the same.

Engine was running quite well and it wasn't obvious that there was any major issues.

kenikh · 02-27-2009, 09:20 AM

Correct me if I am wrong, but I thought that the 914-6 always used the deeper 2 liter head, even after the 911 went to flatter domed head. This could account for compatibility and dates on the heads.

Grady Clay · 02-27-2009, 09:29 AM

Chris,

Are there any other differences in the heads other than the numbers?
Was there a head gasket?
What is the top (sealing surface) of the cylinder like?
Is it 80 mm bore?
What kind of cylinder?
What piston?

An important test will be to measure the combustion chamber volume of all the heads.

I suspect those may be a run of new spare parts racing 2.0 heads built in ’70. Keep in mind that people raced 2.0s for a long time (and still do). It is only the current crop of ‘bean counters’ that don’t value customers.

Best,
Grady

304065 · 11:09 AM

Chris, while you have the caliper out I would be interested to see the valve head diameters. Those heads have been heavily flycut- you can see the casting marks have been worn away on the fins. I bet they have fairly small combustion chambers as a result-- I am guessing on the order of 70cc. By '70 you would think the heads would have an MFI boss in the center, not the '68-style angled air injection boss- so I'm with Grady, these are probably special production replacement parts.

cgarr · cgarr's Garage

If that stamp 84.2 is the flycut then they took off the max allowed at .25mm

Flat6pac · 02-27-2009, 04:22 PM

the 70 is a 914,6 head sealing surface. The later 2.0 heads had larger valves about 1968
Bruce

chris_seven · 03-04-2009, 12:08 AM

Have been away for a couple of days but in answer to some of the questions;

The heads/cylinders have a head gasket as per 2.0 litre engine as is the top sealing face.

Bore is 80mm.

Barrels are Nikasil

Pistons will be custom 906 style made in UK with moly coated skirts etc.

Will measure valves a little later today.