early and late model SC cams in my 78?

[Brown747]

Just did my first drop to go after a broken head stud. I got the cam covers off and found that it has early and late style SC cams.. Car is a 78 with good records from the PO. I can see where it was torn down before for a broken head stud but the work order makes no mention of any cam work. Could the car have rolled out new with both types? I've got the 46MM crows foot and the P202 tool but now have to get the P9191. Anyone in the Seattle area have one I could borrow or rent?

TIA Thor

[tom1394racing]

Thor

The bolt style cams did not come out until '83 so it is not likely that the engine came from the factory with the bolt style on one side.

Your chain boxes were opened up at some point to install the Carrera tensioners. Probably had worn or pitted cams lobes and the PO decided to change out the cam.

[Flat6pac]

You can probably buy the cam you need for less than the price of the tool.
Bruce

[fred cook]

I have read that the cam nut to bolt change came in late 1980? Yes, no, maybe??

[Brown747]

I pulled out all the old receipts and work orders and find no record of a cam ever being replaced. I do have a record of LT side teardown for a head stud and record of the tensioner upgrade but nothing about cams...particularly on the right side????

PO owned the car for 27 years and I've sent him an email asking if he has any recollection
of a repair.
TJ

[BURN-BROS]

One possibility...The snout of the cam broke off and was "updated" to the later style. It happens when either installing or removing the big nut, The other cam should have been modded for symmetry.

[Henry Schmidt]

Give me a call. I can exchange the one you don't want, or modify the early cam to match the late style.
If the engine was repaired with Supertec head studs, the engine would not be coming apart for a broken stud a second time.

[boyt911sc]

Originally Posted by fred cook

I have read that the cam nut to bolt change came in late 1980? Yes, no, maybe??

Fred,

The '78-'81 SC engines use the crowfoot tool (P-203) while the later '82-'83 SC use P-9191 tool also used for the 3.2 Carrera. HTH.

Tony

[tom1394racing]

Tony is correct....I just checked my PET. The change to the bolt type cam was in 1982.

[Brown747]

Got an email back from the PO who claims that he has no knowledge of a cam ever being replaced in the 27 yrs that he owned the car. That would leave the period from when it was new up to 40,000 miles in 6 yrs.. Not likely is it that there would have been a need to open it up then and the records from his time period do not reflect any major work. Leaves me wondering??? And in need of a P9191.
Thor

[Walt Fricke]

I have a 1982 3.0 motor. Stock US type. In preparation for rebuilding it I bought the tool for the bolt type cam. When I opened it up I found big nut cams. Which was fine with me, as I have got timing those down pat. But a surprise.

When did the cam journal size change? And when did Porsche go back to 4 bearing cams? I know the 3.2s used the 4 bearings, with the larger journal. What I am getting at is the question of whether you can just swap SC cams back and forth between nut and bolt types, using the same cam carrier.

Porsche is (or was) notorious for using up old stock it had on hand. Maybe it came from the factory this way? They ran out of the new cams that week, but had old ones and carriers? In some ways, older 911s are a bit like the human body - we all know our hearts are on the left side, but occasionally a physician finds one which is on the other side, but is working fine.

[boyt911sc]

Thor,

I also have a '78SC engine with broken head studs that I bought from a Pelican Parts member. See pictures below:





Do you want to trade one of your cams? Sorry, I forgot that I already dumped the old worn-out SC cams for 964 cams.

Tony

[BURN-BROS]

Originally Posted by Brown747

Got an email back from the PO who claims that he has no knowledge of a cam ever being replaced in the 27 yrs that he owned the car. That would leave the period from when it was new up to 40,000 miles in 6 yrs.. Not likely is it that there would have been a need to open it up then and the records from his time period do not reflect any major work. Leaves me wondering??? And in need of a P9191.
Thor

If the snout broke off, the cam can be machined to accept the later bolt setup. During the early SC period there was a bad batch fo valve springs that may have led to a early valve job? Work was done on that motor and it was not at the factory.

Compare the rust on the 123 sprocket/hardware vs the 456....

[Brown747]

Originally Posted by BURN-BROS

If the snout broke off, the cam can be machined to accept the later bolt setup. During the early SC period there was a bad batch fo valve springs that may have led to a early valve job? Work was done on that motor and it was not at the factory.

Compare the rust on the 123 sprocket/hardware vs the 456....

Aaron,
The pictures that I believe you are referencing are from Tony's post. No rust evident in the pictures of my cams at the beginning of the thread. Is it possible this could have been early factory experimenting before going into production use? The cam bolt/gear would not need to come apart for the tensioner upgrade would it?
Thor

[Brown747]

Thanks for all the input BTW..

Thor

[BURN-BROS]

I just checked your photos and although you do not have rust you can see a visual contrast between the cam sprockets and hardware between the left and right side. This contrast is also in Tony's picture. The left sprocket and nut are brown with oil deposits and the right is relatively clean. Your second pic shows that contrast between the idler sprocet and the cam sprocket very well.

I have witnessed cam snouts break off at least 3 times....

The cam nuts would not be removed when changing tensioners.

In my opinion Porsche would have never delivered an engine with different cam designs.

There are other scenarios in which you could have a differnt cam but this is most probable.

I would take Henry up on his offer to mod the left cam so that it matches the right as it is a better design than the old big nut setup.

[Brown747]

Thanks Aaron for your observations.

Thor

[Flat6pac]

All three liters and larger use the cam carrier with the 4 bearings, including the 76/77 Carrera 3.0. The lobes are larger and made it necessary to make larger bearings.
Years ago, I had the machine shop cut the bearings down to work in 3 bearing journals and the lobes wouldnt go in through the journals.
Bruce

[BURN-BROS]

Originally Posted by Brown747

Thanks Aaron for your observations.

Thor

LOL, no worries. In the end it's not really important how it happened.

Good luck with your project!

[Henry Schmidt]

One more quick observation: As you can see the tensioners were upgraded but not the tensioner arms. The greatest threat to tensioner life (save excessive heat of course) is tensioner arm binding. That is why Porsche updated the arms when they introduced the pressure fed tensioners.
Our host sells the updated arms.

If they are not available through our host you can get the Supertec arms from us.