1973.5 2.4 cis top end rebuild !

gibran911 · 08-18-2011, 03:41 PM

Hello, My name is Gibran and I have posted here a few times for information about my 1973.5 T Targa which I am attempting to resurrect after about 18 years of hibernation in the Arizona heat. I Bought the car last November and have had several hurdles to over come with this car. Some have been remedied while others will still need tending to.

At the moment, I have pulled the engine and removed the top end in order to diagnose low compression and poor leak down numbers on #4 and #2 which hinted at bad rings. As the tear down progressed, it was clear that this engine was rebuilt just prior to it being parked as the parts and labor listed on the repair receipt dated 1991 detailed.

Upon inspection, the #4 and #2 cylinders have pitting on the bottom of the barrels. I attribute this to moisture getting into the cylinders as these two would be in the intake position perhaps when it was parked. The photos show this:

My question is, can these cylinders be repaired and reused? If so, who do I send them to? My attempts to find out more about these pistons and cylinders has come up NLA?
Any advise from the experts out there would be greatly appreciated.
Thanks You,
Gibran

E Sully · E Sully's Garage

I will be going through this soon also. My '73 cis engine will be taken apart this winter. There is no way to tell for sure by looking at them, you will need to have them measured by a machine shop.
You might want to post a question in the technical forum about who is a reliable shop in your area to go to. The machine shop can take a look at them and see how they measure up.
They are steel cylinders so if they are not worn you should be able to hone them and reuse them. If they are worn too far, they can be bored oversize. You could always get a set of JE pistons and rings to fit if they are worn out of spec. As far as '73 cis pistons and rings, they were a half year only item. I don't think original replacements are available anymore, unless you get lucky finding someone selling a set. There was an add in the classifieds a little over a year ago where a set of nos pistons, cylinders and rings were offered for $1,800.
Hopefully they will all be good and you can reuse them. I will be following this so I can get an idea of what I'm in for.

tom1394racing · 08-21-2011, 05:36 PM

84V58 are the Mahle 2.4 CIS pistons and are correct for your motor.

The cylinders are the cast iron 84mm cylinders and are also correct.

When these engine sit for a long time without being turned and lubricated, the piston rings corrode with the cylinder bores. If the corrosion pitting in the cylinder bores is not too bad, they can be honed and re-used.

If you need either replacement cylinders or pistons, contact me as I have some good shelf stock on both.

gibran911 · 08-21-2011, 06:35 PM

Thanks guys for your input. I live in Tucson, Arizona and have a good machine shop in mind.
I should know something by next weekend.
Stay tuned for more.

Gibran

deathpunk dan · 08-25-2011, 04:09 AM

Could you have them bored out to 85 or 86mm and just order up some JE pistons?

E Sully · E Sully's Garage

Would stock cis intake and cams work well with JE pistons?

gibran911 · 09-10-2011, 02:53 PM

I think with the CIS system, no alterations to the piston size , cams, or crank are possible. which leads me to my next question.
I am still trying to make it to the machine shop as family matters took up most of my time the last few weeks. So I do not have an answer as to whether or not the cylinders can be reused, but.....
Is it possible to use 2.4 mfi cylinders? The cis pistons are fine and the rings are available, as far as I understand the 1973.5 cis piston is the only difference. Would this be possible?

Flat6pac · 09-10-2011, 04:19 PM

All the cylinders are the same for the 911T from 70 through the 73.5cisT. Cast iron.
Bruce

gibran911 · 09-13-2011, 01:08 PM

Thanks Bruce.

Just dropped off the top end at Machine Works.
Looks like just honing the cylinders should solve the issue.
Having the heads checked and new valve guides and seals installed as well.
So far it looks like it should be good to go next week.
Stay tuned.

jyporscheboy · 09-15-2011, 08:22 PM

Hi Gibran
Do you plan on using the CIS ? Before the tear down did you have the motor running ? I have a 1973.5 T and have had nothing but trouble with the CIS since i got it 10 yrs ago . Do you have someone to help with it in Tucson ? I live in Phoenix . Is Machine Works doing the valve guides ? Were the guides worn ? later John

gibran911 · 09-16-2011, 05:59 PM

Hi John, Yes I am using the CIS and the car was running prior to tear down - aside from a problem with the fuel distributor which was repaired ( there is a thread on here about it.). the reason for the rebuild was low compression and leakdown #s.
Chris at the volkstop is a good friend and so far we have figured out what to do.
Yes, Machine works has the jig to rebuild the heads. putting new guids and seals in now, while its open.

jyporscheboy · 09-16-2011, 08:19 PM

Hi Gibran ,,
Thanks for the info,, I hope that the motor goes back together quickly ,, Are you going to do the assembly ? Do you know how to do the cam adjustment ? later John

E Sully · E Sully's Garage

Glad to see it didn't need new cylinders and pistons. Are you installing new rings? The rings for the 73 cis are unique and I am wondering about their availability and cost.
I had the valves done when I first got mine when a chain tensioner failed and it jumped a few teeth, bending the valves. I went with the carrera tensioner update.

gibran911 · 09-21-2011, 10:52 AM

Hello,
Just waiting to get the parts back from Machine Works. I Plan on assembling the engine with the help of my friend Chris. Have not timed cams before, so it will be a big learning curve. The great people on this site will surely be needed.
I am looking into rings. The pelican site lists them as well the local dealership. will let you know what they end up costing.
My car already has the tensioner update. Will probably need to go through the brakes before I hit the road.

Gib

gibran911 · 09-22-2011, 11:50 AM

Hi,
Ordered rings from Pelican today $232.50 for all 6 cylinders.
Machine works will have the top end ready next week.
Then the fun begins!

LakeCleElum · 09-22-2011, 08:18 PM

I have a set of like new '73.5 pistons/cylinders/rings....Can still see the factory hone pattern.....Would let go of them as I went with a 3.2 instead of a rebuild...

gibran911 · 10-05-2011, 07:05 PM

Sorry for the long pause.

LakeCleElum, how much for your parts?

Still waiting for mine to come back from the machine shop.

Also, the cams in my car are S spec 143 and 144 if my memory is correct. thought this was not possible to change the T cams with CIS - any Ideas?
The PO stated that he thought the engine was built to S specs at some point by the person he got the car from.

gibran911 · 10-05-2011, 07:45 PM

Hello,
According to the 911 cam table I found at Carquip, the 1973.5 911 t w/cis came with 911 105 141 00 on the left and 911 105 142 00 on the right.
My car has the cams that came in a 1974-77 2.7 S and carrera 911 105 143 00 left and 911 105 144 00 right.
The only thing that seems interesting is that the lobe of the T cam is 38mm on intake and 37.48mm exhaust and the S cam is 38.43mm on intake and 37.38mm on exhaust.

maybe it works as is or perhaps it was ground to stock.

Intrigue!

E Sully · E Sully's Garage

Gibran911,
It sounds like the engine was modded a little bit. Was their a problem getting the piston rings and that is why you need LakeCleElum's parts? I am curious what I will be in for when I start the engine work.

LakeCleElum · 10-06-2011, 07:54 PM

Was thinking $900? PM me please...