broken transmission, any ideas?

[TopsailBeach]

Which shop do you use? If you want a second opinion, Triangle Import Auto on Capital Blvd in Raleigh is awesome. Not cheap, but honest, reliable, and highly knowledgeable and skilled when it comes to Porsches. They have done work on my 911 since 1987. Highly impressive folks.

Good luck!

[brittbolen]

I use Millersport in Hillsborough. I went by and looked at my motor, and that cam tower is definitly damaged. There are chunks missing. Both ends of the rocker shaft had broken off, and part of the rocker arm was missing too. So I'm definitly getting that replaced.

I'm thinking that now might be a good time to get the carrera tensioners installed, especially since chuck will have to disassemble one cam tower anyways.

I'll keep Triangle Import Auto in mind, thanks!

[jluetjen]

Britt;
I've got at least 10 or more cam towers that I don't need. I'm going to be in Greensboro on Tuesday and Wednesday, I could most likely bring one or two down with me. Drop me an email and we can work the details.

- John

PS: Grady, thanks for the great history. BTW, the factory shop manual suggests that Porsche made some slight changes to the 911 gear box starting in 1970 related to the gear and shaft assemblies, I believe to make to make it more robust. They don't say much more then that. Do you know what they did? Are all 901 and 911 gears interchangeable?

[brittbolen]

cool, lots of cam towers are out there, so which ones fit my 2.2L 70E motor?

Here are some photos for those interested... warning somewhat gorey engine damage follows

Here's my broken rocker arm shaft



Diagram, you can see i broke both ends off...


Just look at all the scoring around the bores in these 2 shots, the tower is really torn up...



And here's a (sorta lousy) shot of a non-broken rocker shaft...


Britt

[brittbolen]

The saga continues. It appears that as the rocker arm was flailing about on the broken shaft this caused it to dig into one side of the #4 intake lobe on the camshaft, the grooving is bad enough that the cam probably won't even touch half of the rocker arm when the rocker shaft is fixed.

So this leaves me with the delimma of probably needing a new cam, finding and old cam, or having my cam welded and reground.

My mechanic said that if a got a new cam it would require all new rocker arms. His explaination was that the cam and rockers really need to be broken in together so that the various contact surfaces on the cams and rockers are even. By this logic it would seem that using a used cam would also require new rockers?

How much would it cost to fix my cam? who could do it? (I know of Web Cam) Anybody got a 4-5-6 camshaft for a 1970 911E that they want to sell? I did some reading and Bruce Anderson's book says that 70 and 71 cams are the same, and I didn't see any mention of a change in 70, so possibly 69 cams would also work...

Thanks!

Britt

[Grady Clay]

Britt,

Good that you caught this. Had the valve gotten stuck open, bent, and broken off would have been a major disaster.
This is where some careful research of the prior (poor) repair needs to be done. Sounds like your good mechanic has a handle on things. Check everything reasonable on both sides. Do a cylinder leak test. It sounds like the previous failure was the cam jumped time and broke all the rocker arms. Careful inspection of the sprockets and the aluminum gear on the jackshaft is in order. Has the right chain been replaced (has a removable link)? I would certainly replace all six chain ramps, and rebuild the tensioners. I think Jerry Woods Enterprises makes a safety device that prevents the tensioner from collapsing all the way. Our host may sell that. There is an update for the chain idler arm and idler sprocket.

The right (4-5-6) cam is the same ’69-’71 911E. If you found a good pair of ’72-’73 911E cams, you couldn’t tell the difference.


John,
Sorry I didn’t see your question earlier. We were out of town and the thread escaped.
Yes, there was a change in ’70. Porsche widened 1st and 2nd gears by 0.6 mm and consequently changed the intermediate shaft bearings clamping plate and retaining bolts for clearance.
Yes, all 901 and 911 gears are interchangeable with the above update. Many of the special gear ratios have 904 part numbers as they were first available as race parts for the 904. All the gears also fit the 906 transmission. There is also an entire series of gear ratios that split all the 901/904/906/911 ratios that were designed for the 910. They are all under-cut and cross drilled for weight reduction and had oiling holes drilled to better lube the needle bearings.

I think the reinforced input shaft was introduced in ’67. There were also early and reinforced versions of the 904 input shaft (2nd gear splined onto the shaft.) The 904 shaft was Factory installed in all 901/911 transmissions that were ordered with special gear ratios such as 901/80, 901/81, 901/82, 901/83, and 901/84. There are only two input shafts with 2nd gear cut on the shaft; F (18:34) and GA (18:32).

Best,
Grady

[brittbolen]

Grady, I had already planned to do the carrera tensioner upgrade while the cam tower was being replaced, so I take it you'd agree with that plan?

I had talked with Chuck about making sure that the other 9 rocker shafts were installed correctly, I'll follow up on that Monday (I'm going out for my weekly take photos of broken stuff trip )

Thanks,

Britt

[Grady Clay]

Britt,

I’m not totally convinced that the Carrera tensioners are ideal for all circumstances. The earlier tensioners with a Factory rebuild kit and aftermarket safety device seem to work just fine for a huge difference in cost.
Do a search on the pros and cons of each.

As I understand it:
The pros for the Carrera tensioners are there is constant supply of engine oil under pressure to maintain the tensioner oil level.
The cons are the flow brings in contaminants and the system is more complicated (Murphy’s Law.)
The pros for early tensioners is less expense and less complicated.
The cons are it can run out of oil. When it fails a safety device can prevent any large malfunction.
I would like to hear other’s input on this as clearly even Carrera tensioners fail.

This is a minor issue for you.

You need to find each and every problem or flaw from the prior hack work and age. Of course you can rebuild the entire engine with lots of new parts. The “Art” is to do just what is necessary and prudent and not just throw money at it. This is where careful testing, measurement, and diagnosis are important.
As I said above, the first is a cylinder leak test. Next would be to measure the actual cam timing on both sides. Inspection of the chains, sprockets, idlers, ramps, and jack shaft gear are very important.

After you summarize all the issues, I can give you a reasonable list of “while you are there.”

Best,
Grady

[brittbolen]

Ok, checked out the engine today. The cam is slightly messed up. I'm going to ship it to web cam and they will weld and regrind the one lobe. I'll replace that rocker. The rest of the cam and rockers will be left alone as they're fine. This gets me back on the road without having to get all new rockers and a new cam.

I was pleasantly suprised to see my chain tensioner already had the collar installed. I'm not sure which way to go on tensioners, I have ready some threads about the pressurized ones failing, and not many about the old school ones, but I think that could be due to a skewed sample base... I dunno.

My mechanic will be taking things apart on the other side to make sure nothing is failing there, so far the rocker shafts are installed correctly. He's also going to do a compression test on #4 and pull out the valve spring to make sure the valve guide is ok.

Britt

[brittbolen]

I picked my car up today, and after a bit of excitement driving it home (I apparently lack heat with which to defog my windshield) it is now in the garage!

In the end I got 7 new rockers and shafts, a reground cam, a new cam tower, and the carrera tensioner upgrade.

He also refreshed the clutch pivot mechanism as mine was 35 years old and on the verge of failure.

And I have a new (to me) air cleaner assembly to replace mine, which had one of the cold start drip lines broken off, I'll need to find a replacement or fix mine at some point...

The car is MUCH quieter now, which makes sense since I had that broken rocker clanging around in there. Now my car sounds like a car, and less like a psychotic lawnmower...

Alas I didn't get it back in time for the holiday laps at VIR today, but I think I would have gotten rained on anyways...

Now to get new tires for my new refinished 16x6 wheels, no more dinky 14s.

thanks for all the help and info everyone!

Britt