Stripped cam gear

356 Porsche-related discussions and questions.
Message
Author
Mark Schumacher
356 Fan
Posts: 82
Joined: Wed May 21, 2008 9:15 am

Stripped cam gear

#1 Post by Mark Schumacher » Sat Nov 09, 2019 4:48 pm

Any ideas on what may cause this failure?
Engine is modified with dual valve springs.
Attachments
96B30685-407B-45E3-B0F8-1B1E5657A4DC.jpeg
96B30685-407B-45E3-B0F8-1B1E5657A4DC.jpeg (119.68 KiB) Viewed 389 times

Tim Berardelli
356 Fan
Posts: 349
Joined: Wed Apr 30, 2008 7:02 am
Location: Washington DC Area

Re: Stripped cam gear

#2 Post by Tim Berardelli » Sat Nov 09, 2019 5:42 pm

Mark,

More details, unless you enjoy wags! How many miles on the engine, any recent or last work prior to the gear taking a dump, the barrels look very "fresh". Hope you have a full flow oil filter, if not, you will need to dissemble to the last nut & bolt to find/remove the non-ferrous "pixie dust" that is everywhere in the engine.

User avatar
C J Murray
356 Fan
Posts: 7633
Joined: Fri Oct 23, 2009 7:24 pm
Location: 30MI WEST OF PHILA

Re: Stripped cam gear

#3 Post by C J Murray » Sat Nov 09, 2019 5:48 pm

What do the cam lobes and lifters look like? Were the valves hitting the pistons? How radical is the cam and how much spring pressure were you using? Who made the gears? Is that a groove in the crank gear?
'57 Speedster
'59 Sunroof
'60 Devin D Porsche Race Car - Finally Finished!
'63 GS 2133 coupe
'64 Elva Courier mk4T
'67 911 S Original Owner

User avatar
David Jones
356 Fan
Posts: 3745
Joined: Tue Mar 25, 2008 6:32 pm
Tag: I wish I knew as much as I think I know.
Location: Harrodsburg, Kentucky

Re: Stripped cam gear

#4 Post by David Jones » Sat Nov 09, 2019 6:09 pm

I think I am stating the obvious here but it looks like the camshaft became the immovable object as the crank kept moving probably as a result of the car still being in gear. I will do a WAG that the valve gear is at fault, maybe a seized or bent valve or broken lifter jamming the camshaft.
Bigtime teardown and cleanup regardless.
If I had known I would live this long I would have pushed the envelope a little harder.
Cymru am byth
David Jones #9715

Chuck Allard
356 Fan
Posts: 142
Joined: Mon Jun 01, 2009 2:55 pm

Re: Stripped cam gear

#5 Post by Chuck Allard » Sat Nov 09, 2019 6:24 pm

I've seen that on other grooved cam gears.

Mark Schumacher
356 Fan
Posts: 82
Joined: Wed May 21, 2008 9:15 am

Re: Stripped cam gear

#6 Post by Mark Schumacher » Sat Nov 09, 2019 7:39 pm

Thanks the response:
- This is a 1883 engine with Shasta cast iron barrels/JE forged pistons. I built the engine about 5 yrs ago. Has maybe 12,000 miles. I run 2-3 DE events/yr so it sees RPM’s. Rev limiter set at 6200.
- cam is Elgin 7208. Dual springs because that’s what Walt Watson said I need when he built the heads. Full flow Canton-Mecca oil filter
- Have not yet pulled the sump to inspect cam lobes/lifters.
- Cam gears are stock Porsche far as I know. There is a groove in cam gear, not in crank gear
I do admit to driving the engine hard, but you’re supposed to drive a Porsche hard. Just trying to avoid the problem on the rebuild.

Mark Schumacher
356 Fan
Posts: 82
Joined: Wed May 21, 2008 9:15 am

Re: Stripped cam gear

#7 Post by Mark Schumacher » Sat Nov 09, 2019 7:55 pm

The failure announced itself as what sounded like a valve leak. Car ran strong for a few miles.
Then stopped.
Yes, full rebuild ahead. I live in Minnesota and the winter is long.
Attachments
E8AB3E7C-1E43-4050-BF4D-76F76817D7E7.jpeg
E8AB3E7C-1E43-4050-BF4D-76F76817D7E7.jpeg (93.03 KiB) Viewed 324 times

User avatar
Vic Skirmants
356 Registry Member
Posts: 7154
Joined: Tue Oct 27, 2009 5:02 pm
Location: SE Michigan

Re: Stripped cam gear

#8 Post by Vic Skirmants » Sat Nov 09, 2019 7:58 pm

DON'T groove the cam gear! It only weakens it, and does not produce copious amounts of added horsepower.

Mark Schumacher
356 Fan
Posts: 82
Joined: Wed May 21, 2008 9:15 am

Re: Stripped cam gear

#9 Post by Mark Schumacher » Sat Nov 09, 2019 8:20 pm

I am sure the groove was added or recommended by either a Competition Engineering or by the vendor of the engine parts. I am not smart enough to have come up with that mod myself

Martin Benade
356 Fan
Posts: 4072
Joined: Wed Nov 23, 2011 10:52 am
Location: Cleveland, Ohio

Re: Stripped cam gear

#10 Post by Martin Benade » Sat Nov 09, 2019 8:33 pm

Could that somehow have caused this failure, or is it just a waste of time for the three flypower it gained?

User avatar
C J Murray
356 Fan
Posts: 7633
Joined: Fri Oct 23, 2009 7:24 pm
Location: 30MI WEST OF PHILA

Re: Stripped cam gear

#11 Post by C J Murray » Sat Nov 09, 2019 9:08 pm

Yes it could have caused the failure. Continue to look for anything that could have been binding the camshaft also. Your cam does not require excessive spring pressure but call Dema Elgin to confirm that. If you want longevity you must use as little spring pressure as possible. Often a machinist will spec excessive spring pressure so that the parts don't bang into each other but a well designed cam can often work with stock springs.
'57 Speedster
'59 Sunroof
'60 Devin D Porsche Race Car - Finally Finished!
'63 GS 2133 coupe
'64 Elva Courier mk4T
'67 911 S Original Owner

Mark Schumacher
356 Fan
Posts: 82
Joined: Wed May 21, 2008 9:15 am

Re: Stripped cam gear

#12 Post by Mark Schumacher » Sat Nov 09, 2019 9:21 pm

Dema was very helpful in specing this cam some yrs ago. Go to hear he is still active.
I will do more tear down and investigation in the next few weeks and will post results

User avatar
Don Gale
356 Fan
Posts: 168
Joined: Wed Jul 26, 2017 6:27 pm
Location: Albuquerque
Contact:

Re: Stripped cam gear

#13 Post by Don Gale » Sat Nov 09, 2019 9:31 pm

Just curious, what does a grooved cam gear supposedly offer? Less contact friction, better tooth lubrication, trivial reduced rotating mass?
1958 1600 Super Sunroof Coupe
former 1966 Euro 912 Sunroof
former 1978 Intermeccanica Speedster w/'68 912

User avatar
David Jones
356 Fan
Posts: 3745
Joined: Tue Mar 25, 2008 6:32 pm
Tag: I wish I knew as much as I think I know.
Location: Harrodsburg, Kentucky

Re: Stripped cam gear

#14 Post by David Jones » Sat Nov 09, 2019 9:51 pm

F Vee engine builders did it supposedly to help oiling/lubrication of the gears and to channel away excess lubrication. Kind of catch 22 situation. Sometimes there are many conflicting stories on reasons for doing things. I thought it silly as the cam gear is soaked in oil.
I also question double valve springs. I can hit in excess of 6500 rpm with single springs and the right amount of valve spring shims. Extra seat pressure can easily result in tuliped valves which can break and make everything crater. The sound of a valve leak? before hand could have been a valve sizing in a guide.
If I had known I would live this long I would have pushed the envelope a little harder.
Cymru am byth
David Jones #9715

User avatar
Ron LaDow
356 Fan
Posts: 6558
Joined: Wed Mar 26, 2008 11:45 am
Location: San Francisco

Re: Stripped cam gear

#15 Post by Ron LaDow » Sat Nov 09, 2019 11:00 pm

Don Gale wrote:
Sat Nov 09, 2019 9:31 pm
Just curious, what does a grooved cam gear supposedly offer? Less contact friction, better tooth lubrication, trivial reduced rotating mass?
Supposedly relives trapped oil, but I really don't see an escape path.
To be honest, if you had spent many hours on a dyno and optimized everything else, it would be worth testing one. It wouldn't take long so you should have pretty good A-B comparisons.
Ron LaDow
www.precisionmatters.biz

Post Reply