Broken camshafts

[911korjaaja]

I was torquing up my right camshaft nut to 150Nm when it snapped in two pieces. It was cut just where the tread starts on the shaft.

I would like to hear if any one has had similar faults on their shafts.

Only luck here was that it happened on my engine mount not while firing up the engine.

Car is -73 2,4T

[svandamme]

i think you overtorqued things a tad

where did you get that value from??

this is from the Porsche workshop manual ,
911 early till 84

[911korjaaja]

I took the torque from the from the book How to rebuild and modify Porsche 911 engines 1965 - 1989. 150Nm came from section 6 Sprocket assembly.

Too bad, have to find replacement camshaft now.

[svandamme]

hmm

there are errors in the first print
http://www.101projects.com/911-Rebuild/corrections.htm

Page 154 - The cam tower nuts should be torqued to 75% of the value listed in Appendix A.

don't have the book with me now , so can't verify what the actual value in the book is , and but 75% of 150 NM , would be 112.5 NM, which is pretty close to the 12 from the workshop manual...


was this a new cam ? or an old one??

technically , with new cams, you also need new rockers
since the old ones will wear the new cam to fast
that might be a bit to much for a T, maybe you can score a second hand cam , with matching second hand rockers...

[Gunter]

Originally posted by svandamme
i think you overtorqued things a tad

where did you get that value from??

this is from the Porsche workshop manual ,
911 early till 84

Until about 1982, SC 3 liters had the big nut (150 Nm is correct).
After '82. the big nut was replaced with a 12mm center bolt plus big washer. (120 Nm)

Your picture shows a cam with the 12mm bolt, P9191 tool needed.
The big nut requires a 46mm crowfoot, and P202, and lots of oomph to get the 150 Nm. (120 ft-lb)

He did nothing wrong, just a bummer on material-failure.
I would try and get the later cams with the 12mm center bolts, much easier to handle. (Just noticed it's a '73 which has 3-bearing-cams, no center bolt available, has to stay with the big nut) Used ones might be obtained on the PP board.

[elflamo]

Maybe your torque wrench needs recalibrating?

Dennis

[shbop]

Look carefully at the nut. Both sides. Is it possible that somewhere down the line the nut was interchanged with one that had the eccentric for a fuel pump? Installing it backwards will do exactly what you see.

[thechiller]

The same thing happend to me today, it was the camshaft on the right side went in two pieces. I have a SC 3.0, 204hp. Now i need a new camshaft. I considering to buy a some this racing camshaft on e-bay
http://cgi.ebay.com/ebaymotors/Super-Cup-cams-Porsche-911-930-964-camshafts-cam_W0QQitemZ160023736695QQihZ006QQcategoryZ33614Q QssPageNameZWDVWQQrdZ1QQcmdZViewItem

Will these cams give me more hp? or can these cams just case me any other problems?


Kjell Robert

[88-diamondblue]

Give John at www.drcamshafts.com a call or email. The ebay link you gave was for DrCamshafts he posts here as Camgrinder. He did my cams and rocker refurb. Highly recommended and knows his stuff. Depends on what you want from your engine check out the website. Do a search on cams, lots of reading.

[kenikh]

Ditto DR Camshafts. John is the man.

[Gunter]

Originally posted by thechiller
The same thing happend to me today, it was the camshaft on the right side went in two pieces. I have a SC 3.0, 204hp. Now i need a new camshaft. I considering to buy a some this racing camshaft on e-bay
http://cgi.ebay.com/ebaymotors/Super-Cup-cams-Porsche-911-930-964-camshafts-cam_W0QQitemZ160023736695QQihZ006QQcategoryZ33614Q QssPageNameZWDVWQQrdZ1QQcmdZViewItem
Will these cams give me more hp? or can these cams just case me any other problems?
Kjell Robert

The cams on eBay may be too hot for CIS.
Get in touch with camgrinder for help.
If you keep CIS, you are limited with choice of cams.
I would put a WTB: SC cams, '81-'83 3-liter on the Pelican board.
After '81, the cams come with a smaller center bolt instead of the big nut; much easier to work with.
After you find used SC cams, have them reground to 964 profile which your CIS will tolerate. Ask John (Camgrinder) for advise.

[MBEngineering]

HI the reason the end came of is that the large washer was not located in the chain wheel correctly and when tightened up snap's the end off, to sort the prob' out you will require a bolt and washer from a later camshaft and a trip to the local engineer's to clean up the end of the cam and drill and tap the end to fit the bolt, then back to fitting the cam and timing with the late cam gear holder to tighten every thing up. good luck

regards mike

[Gunter]

Good thinking Mike; that could work because the end-play of the cam is not affected with this repair. It's worth a try.
Get the right center bolt and washer from the later SC-cam.
It has to be the right washer to hold the cam sprocket.

[MBEngineering]

HI Gunter it's not 'worth a try', IT works, i have repaired snapped cams and re fitted them OK with the late SC/3.2 washer and bolt with no prob', i did copy the end of a late cam shaft for the clearances in the bolt hole, have fun

regards mike

[Superman]

I have a pair of '83 cams that I will never use. Perhaps I should put them on the classifieds page.