964 Engine rebuild questions

[ALEX P]

Hi

I'm in the middle of rebuilding my early 964 engine to install into a 1985 body and I'm carrying out a few upgrades whilst in there.

The reason the engine is being rebuilt is because of a snapped head stud, poor leakdown figures on a different cylinder and lack of history with the engine.

At the moment the engine has been disassembled and I'm in the process of cleaning up the various parts to see what needs replacing and what can go back in. I had my local specialist look at the heads, pistons, cylinders, cams, and rockers - The good news was the P & C's were fine, the bad news was both cams and 5 or 6 rockers had wear and slight pitting on the lobes.

The cams and all rockers will be resurfaced and the profile changed possibly to a DC21 with a 114 lobe centre.

I've been mainly working Wayne Dempsey's Engine rebuild book but this only covers up to the 1989 3.2 engines. I'm just getting round to checking the amount of wear on the valves to see if they need replacing and a quick measure of the crank so I guess my first questions are:

All the measurements in the Wayne Dempsey book are for earlier models - Does anyone know where I can get all the measurements and tolerances for a 964 engine, the first thing I was going to measure was the crank?

Similar question regarding the valves - What measurements and tolerances do I need to take to ascertain whether the valves are reusable or need replacing?

The engine has certainly been fully rebuilt before as the case, pistons, con-rods etc have all had machining work carried out on them.

Thanks

[Flieger]

Sounds like someone was using inferior oil to cause the cam and rocker wear. Not enough zinc, phosphorous, and/or molybdenum.

[ALEX P]

A few people have said the main reason for the wear is inferior oil.

As I said, unfortunately the engine came with no history so I have no clues what sort of life it's had - some of it is in good shape and some of it is 'disappointing'.

It's clearly been fully rebuilt in the past so what I'm trying to work out is whether items like the valves were replaced or just re-seated. The safe option is just to replace but there is obvious cost involved and if they are still well within limits then maybe keep them?

[brads911sc]

Always replace exhaust valves. Regardless of how they measure. Every good engine rebuilder recommends this...

[ALEX P]

Okay, thanks brads911sc, new exhaust valves it is, I've been toying with the idea of replacing the inlet valves for the larger 993 RS ones but need quotes for re-machining the heads for the larger seats before I take the plunge.

I had a measure of the crank at the weekend using digital vernier as I don't have a micrometer that size. I put the results against the dimensions in the book but the main bearings and the rod bearings while being consistant, don't measure up as per the 3.2 crank unless mine is undersize?

On a seperate note - Does anyone know what the part number is for ARP rod bolts to replace the standard items?
I've had a look and think it's 204-6005 but want to confirm before I order the wrong ones!

Also - What sort of difference is there between steel and titanium valve spring retainers? (apart from about $300!)

[AlfonsoR]

I don't know what material the new steel ones are made of, the old one was supposedly sintered steel that had propensity for cracking on over reved or high mileage engines. I have seen the titanium material recommended several times on this forum. Besides being an alloy and not having the propensity to crack as the originals, it is also significantly lighter.

Since these would weigh so little, it might be worth to get a quote from Steve Weiner at Rennsport systems: Welcome to Rennsport Systems, Porsche Performance Products for the 21st Century

He is very competitive in price because he knows little tricks like, use 993tt heads studs with 964 nuts so you don't have to buy separate washers, they are built into the 964 units. He is very knowledgeable.

I imagine you will probably have your heads rebuilt in the UK, but if you are considering someone here in the US, in no particular order and based on comments I have seen here (not personal experience):

1. again Rennsport systems
2. William Knight : Knightrace Performance-About and Contact Us
3. member on this forum by the user name: cgarr

[ALEX P]

Thanks for the recommendations AlfonsR, I will try to get the work done in the UK if possible as I think shipping and tax on re-importing it make it too expensive otherwise.

I went for the Supertec headstud kit in the end as it came highly recommended and seem a better deal than the 993TT or Raceware ones.

Quick bump for earlier question:-

Does anyone know what the part number is for ARP rod bolts to replace the standard items?
I've had a look and think it's 204-6005 but want to confirm before I order the wrong ones!

[EBS_Don]

Correct, 204-6005. These fit 3.2/3.3/3.6 air cooled motors. 204-4206 for the head stud kit if you're looking for alternative there as well.

[ALEX P]

Thanks Don, even ARP wouldn't give me a straight answer when I emailed them!!! If there's not a lot in it then I'll certainly put the business your way.

Couple of new questions:

The pins that hold the alternator strap in place - do they simply tap out and if so is there a specific direction they need to be tapped?

Some of my case studs have corrosion on them. This varies from simply not having the plating on them anymore to being completely white or having rust patches. Is it common practice to replace these studs or would I just get away with cleaning them up?

[Spenny_b]

Hi Alex, sorry can't be of any help with your questions, but like you, I'm working my way through Waynes excellent book in anticipation of getting a particular 964T that I have my eye on, that's probably in need of a rebuild...up to Chapter 5 so far ;o)

Did you establish whether or not your crank journal measurements are in accordance with earlier <89 specs?

Does anyone know if Wayne is planning on updating the book for 964/993 owners?

Anyway good to know that somebody pretty local to me is also taking the brave pills and having a go themselves (...ie, I may well be in touch at some point in the future!!)

Cheers
Spencer

[Spenny_b]

Meant to say, wrt to Ti valve retainers, my natural reaction would be to do it, whilst you've got the engine in bits....but...my only experience with that is when I had 2 cracked retainers on my Vaux 2ltr "redtop" in my Westfield, some years ago...at the time, the internals were stocks, but even so, didnt want to just replace 2 of the 16 leaving 14 suspects (if a dodgy batch), so IIRC the head was whipped off (easy) and I fitted Ti replacements. Refitted cams, head, re timed, and I have to say it did feel a smidge different (stock internals but SBD taper throttle bodies, MBE management, 4-1 exh man, 209hp). Was then able to reuse them a couple of years later for the "special build" (272hp) that revs to 8750

So, if it were me, I'd go for it.

[ALEX P]

Originally Posted by Spenny_b

Did you establish whether or not your crank journal measurements are in accordance with earlier <89 specs?

Hi Spencer, I'll find out the differences between the earlier specs in the book and the 964 at the weekend and let you know.

I am tempted with the titanium jobbies just not the extra $300 or so! Then it's a case of which ones to go for as there seems to be quite a few to choose from.

I think I'm going to tackle the rebuild in two parts and concentrate on the bottom end first then when it's all together start looking at the top end as that's where all the real tuning options seem to be depending on the size of your cheque book!

Nobody got any advice on my case studs??

[vmisquez]

I replaced all of then when I did my 930. They had no rust but were 20 years old.

[ALEX P]

Originally Posted by ALEX P

Hi Spencer, I'll find out the differences between the earlier specs in the book and the 964 at the weekend and let you know.

Hi Spencer, found out the crank dimensions:-

For 3.2 d1 (std main bearings) = 60.020 - 60,059
d2 (std rod bearings ) = 55.020 - 55.059

For 964 d1 (std main bearings) = 59.971 - 59.990
d2 (std rod bearings ) = 54.971 - 54.990

My rough vernier measurements really aren't even close to being accurate enough, I just took them to get a rough idea. I'm going to measure it properly tomorrow at work if I get time.

Thanks vmisquez, they're going to be replaced as I have no idea how old they are, just not sure which ones to replace with!

On a seperate subject - Has anyone changed their valves to the lighter 993 ones with the 8mm dia shaft when rebuilding a 964 head. If the guides are shot and need replacing it seems a sensible enough 'upgrade' to do???

[Flat6pac]

I had a particular 993 valve needing replacing and it was very expensive, several times the 964 prices.
Your 3.2 numbers are flawed, not correct. All standard sizes end in the .971 to .99

Bruce

[Flat6pac]

Cqrrera used 964 main bearing and the 964 uses 930 rod bearings.
Different cranks, same bearings judging by the part numbers.
Bruce

[ALEX P]

Originally Posted by Flat6pac

I had a particular 993 valve needing replacing and it was very expensive, several times the 964 prices.
Your 3.2 numbers are flawed, not correct. All standard sizes end in the .971 to .99

Bruce

Hi Bruce,

I thought that replacement valves were quite reasonably priced as per the link below, well, the Intervalves ones not the Porsche ones, they are VERY expensive!!

Porsche 911 Pistons, Cylinders and Heads - Page 2

I've stuck the crank info below but will check the dimensions with my specialist at the weekend anyway, hopefully your right as mine then falls into tolerance
Had a quick look at one of the big end shells and it had the number 930 147 01 which seems to be missing three numbers to me.

[ALEX P]

Quick question to anyone who might know - The previous owner has either cleaned up or enlarged the inlet ports on my heads. I gave them a quick measure and they are around 42mm dia, is that the stock size?

[ALEX P]

I was reading a thread about harmonic balancers and it got me thinking - When I bought my 964 engine it had no harmonic balancer so I sourced a secondhand one and was planning on simply fitting that.

One thing that I have noticed about them is that they have different amounts of drilled holes in the front presumably for balance.

This must mean that the one I have bought is balanced to a different crank and needs to be rebalanced.

Does this mean that the best way to balance it is to dummy mount the flywheel and the pulley with harmonic balancer to the crank either in V blocks or in the case half and try to find a 'low point' where it settles then carefully drill the harmonic balacer a bit at a time until it seems weight matched or is there a better way that anyone knows of?

[Flieger]

I thought it was the 993 that had the external balancer. Either way, I would not try to do my own static balance on a harmonic balancer. It needs to be done by someone with the right machine to spin it up.

Flat 6 engines are naturally pretty balanced without a harmonic balancer so I doubt you would be able to do anything statically- it would seem to already be balanced. The harmonic balancer is meant to quell the harmonic vibrations that result from all the various small vibrations interacting and resonating at certain rpms.