964 Engine rebuild questions

[ALEX P]

No, I think they strengthened the crank for the 993 so it's just the 964 that needs the harmonic balancer.

It must be a fairly substantial balance or weight difference between the harmonic balancers. If you look at the photos below, the first show a friends engine and his harmonic balancer, his has one drilled hole and the second photo shows mine with seven! Although the group of three tightly together don't look as 'factory' as the other group of four.

When companies offer a balancing service on a crank then surely it must be done with the flywheel and pulley in place? Anyone have any knowledge to how this is done?

[MBruns]

When doing the balance work on most engines (excluding externaly balanced) you want to zero balance all the components seperately, so if the FW or pulley need replacing you don't have to involve the crank to get it done, you can also zero balance the press. plate so it does not have to be indexed a certain way.
Your question regarding the 930 style cranks the main diff. is they have full size counterweights on all throws, take a look at a 964 vs. a pre 3.6 crank and you will see.

Mike Bruns JBRacing.com

[ALEX P]

Thanks Mike, it just surprised me with the amount of difference between the two balancers. Do you think it's worth putting the crank on a pair of parallells on a surface table just to see if there is any bias?

I don't expect any in the crank and very little in my fairly lightweight Patric Motorsports flywheel but that pulley with the harmonic balancer and those holes make me a bit suspicious!

[MBruns]

Alex I have a few of those units around here and both have 4 or more holes in them, my guess is the factory zero balances them as well, as far as the crank goes do a run out inspection to verify, Its very rare that a stock 911 crank needs much correction if any balance wise. In the past I used a shop that had the old strobe light system, the first 911 crank he spun up didn't even light it up, he thought the bulb was bad....Nope

Mike Bruns

[ALEX P]

Does anyone know what the part number is for the sealing ring between the oil pump and the flange on the pickup shown below in red?

[winders]

Originally Posted by ALEX P

No, I think they strengthened the crank for the 993 so it's just the 964 that needs the harmonic balancer.

I seem to recall that the 964 crankshaft is preferred to the 993 crankshaft in performance builds. Is that not correct?

Scott

[ALEX P]

Has anyone got any tips for removing the old exhaust gaskets from the head, some of them are completely stuck in there and I don't want to damage the edges of the groove by trying to prise them out with a screwdriver or similar?

[ALEX P]

After speaking to a very experienced engine builder, he recommended that because I've got a new harmonic balancer and new (Patric motorsports) flywheel I should probably get the whole lot balanced, whether that was done seperately or as an assembly I don't know but I'm glad I did as they had to take a reasonable amount from both the flywheel and the harmonic balancer as shown below.

[ALEX P]

The final spec for my rebuild is:

Modified / Flowed case
Modified / Mooned stock cylinders
ARP rod bolts on weight matched stock rods
Weight matched stock Pistons
Lightweight Patrick Motorsport flywheel
993 RS Inlet Valves
993 Stock Exhaust Valves
Race springs with titanium retainers
DC21 cams with 114 lobes
Head inlets lightly ported (done by previous owner)
1.750" dia Headers
Lightweight fibreglass tinware
Exhaust / muffler TBD, 2-in 2-out probably.

My engine rebuild is progressing but I've got a problem - There is no piston to valve clearance. I'm not sure whether the problem comes from the DC21 cam, the 51.5mm dia inlet valve or a combination of the parts I have used for the build.

I know the profile of the stock 964 pistons that I am using don't have the pockets that the RS valved pistons have but didn't think it would be that close. I think that machining the pistons for clearance screws up the compression ratios so I'm looking for advice or opinions what the best way forward is?

Anybody got any ideas?

[MBruns]

You only have two choices, either buy a set of pistons like Je with big enough pockets and trim dome if you need to acheive the CR you want or figure out how much needs to be machined from the stock pistons, but first you have to figure out where the center of the valve is on the piston then the depth and dia. take 2 heads both bare is fine, and a cam tower, place a piston at TDC with the 2 heads on say #1 & #3 with the tower all snugged down to position the heads, with the piston at TDC take a transfer punch that fits the guide like the valve (transfer punches have a point like a center punch) place it to the piston and make a mark for reference on each pocket, then you need to have some one with a piston vise set it up and machine a pocket big enough with at least .040 clear. on the OD. If you have zero V to P now or very little touch and cut .020 to start there. This all depends on how convienant the machine shop is, only to find out that you now have 9 to 1 and no dome thickness, I would buy pistons that are designed for more cam and CR

Mike Bruns JBRacing.com

[ALEX P]

Hi Mike, thanks for the detailed response. So the gamble is to machine the pistons and possibly wreck them or gain my required clearance and run the risk of ending up with a poor compression ratio OR put my hand in my pocket and buy a set of JEs costing around, what? $1k?

Damn, I really didn't plan or budget for that!

From my build spec do you know where it is that I screwed up? Was it always going to fail with that combination of parts?

[MBruns]

Alex, the big inlet valve and the cam is just too much for what you have, even when there is enough room its not much, 2mm on ex and 1mm on in. at bare min.
Mike

[winders]

Lesson for others: This is why you do engine projects like this with folks that "have been there, done that". You just can't pick a bunch of parts and expect them to work together.

Scott

[ALEX P]

Thanks a lot for the advice Mike, I'll have a think and see if I want to play the risky CR gamble or take the safe but expensive JE route.


Scott Winders - Dude, there are some things you should write and there are some things you should just keep to yourself.

[winders]

Alex,

I am sorry for your situation. But this is a great example for others to learn from as to why one should work with an experienced Porsche engine builder when contemplating non-standard projects.

Can't handle your project being held up an example? Don't post it.....

Scott

[Steve@Rennsport]

Originally Posted by ALEX P

Thanks a lot for the advice Mike, I'll have a think and see if I want to play the risky CR gamble or take the safe but expensive JE route.

This is one we do all the time.

Your OEM pistons can be machined for RS valve clearance by carefully widening the intake valve pocket. You'll need to make some measurements to know how much to remove, but its very doable.

[ALEX P]

Thanks Steve, I had a chat with my engine builder he wasn't too happy to do the machining to the pistons as if it lowered the compression ratio then the rest of the build would be kind of pointless as I may as well have just rebuilt it stock and I would have to then buy the JE pistons anyway and my original set would be worthless on top of having to pay the machining costs.

At least this way I'll get a bit back for my stock pistons, wrist pins, clips and new rings. I'll also gain a bit of compression ratio and if I want to go to throttle bodies at a later date then big numbers start becoming easier - If that makes sense?

Thanks again all.

[ALEX P]

Picked up my long block today, really happy with the work. Time to start getting the rest together now!

[ALEX P]

Can anyone help me with the torque figure for the nuts on the 18-studs that hold the inlets in place?

Also the torque for the nuts that hold the engine cover in position or doesn't this matter?

I've been through my books over and over and can't seem to find it anywhere!

Thanks in advance

[964Cab]

Hi,

How is the engine rebuild going ?