Valve timing

[cfm65@me.com]

Hi Guys,
Please help with my valve timing issue.
With the bottom end on TDC (crank pulley on '0') I notice that the cam has passed the upper cam index by a few mm, in other words the valve timing is a few degrees before TDC.  I dont think it is enough to retard by one tooth.
Your opinions and suggestions are much appreciated.
Regards
Chris
Cape Town

[cfm65@me.com]

Hi Gents,
While waiting for your expert advice, I went down stairs and took another look.
With the cam indices ligned up, I found the crank pulley about 14 degrees BTDC. Obviously one tooth out. Slipped a tooth and now with the cam ligned up, the crank is about 4 degrees ATDC.
In other words, the cam is about 2 degrees late( crank TDC= cam 2 degrees before) Does this warrent concern, may be an offset woodruff key, or is it acceptable?
Regards
Chris

[Benz Dr.]

Each tooth is 18 degrees. If you are BTDC the valves will hit the pistons. You can be right a TDC or ATDC but never before TDC. An offset woodruff key could be used to line it up perfectly but that really requires a degree wheel on the cam gear and a dial gauge on one of the intake valves.

[cfm65@me.com]

TKS Doc,
I suppose I can live with a degree or two. Let's leave it as is, unless you can convince me an offset woodruff key would get me a few exrta horses.
Regards
Chris

[Benz Dr.]

TKS Doc,
I suppose I can live with a degree or two. Let's leave it as is, unless you can convince me an offset woodruff key would get me a few exrta horses.
Regards
Chris

I can't say it will and I won't say it can. Not that hard to check and it could be close or a long ways off. We aren't building F1 engines here............but it could give you a bit more HP.

[cfm65@me.com]

TKS again Doc,
Have a great weekend.
Chris

[Shvegel]

Any metal removed during machine work to flatten the head will make the cam late a bit.  If you are moving the cam closer to the crank it will create a little slack that will cause the cam to be a touch late.

[ja17]

The engine will run fine with some late valve timing. Off-set keys are a hassle and usually make no noticeable difference. Never allow the engine to run BTDC. If you were able to just "slip" the chain without removing the tensioner, then the chain is stretched way too much and it should be replaced.

[cfm65@me.com]

TKS Joe,
I have had dealings with off set woodruff keys in a previous life.  And no,  slipping a link  was a figure of speech.  I installed a new chain, just in case, and I had to loosen the tensioner to 'cut' me some slack in order to make ends meet.
I have put it all together, closed up and she is running just fine.
Thanks for the heads up anyway.
Regards
Chris
Cape Town

[Tyler S]

If material was removed from the head you can also shim the cam bearing towers the amount that was removed. This will locate the camshaft to its original height and bring the timing back to spec. No need to deal with an offset key.

[Benz Dr.]

If material was removed from the head you can also shim the cam bearing towers the amount that was removed. This will locate the camshaft to its original height and bring the timing back to spec. No need to deal with an offset key.

Yes, and sort of no.  All this is assuming that the crank gear and other gears are not worn which I can imagine they would be. The only way you can tell if your cam is in perfect time is with a dial gauge and a degree wheel.

I have my intake valve set to open at 12 degrees BTDC which is about as much as you can advance the cam and not run into trouble. I had to use an offset key to obtain this timing as the regular key was off about 6 degrees. On a regular build it was only off by 2 or 3 degrees but I wanted to advance the specs to max or similar to the euro 280 cam. 

[Howard Long]

Mr. Benz Dr.

I realize that this has probably been discussed but being an old hot-rodder, I an curious as to whether any after-market high-performance cams are available for the 280SL.  I am not thinking of a racing cam, just descent low rpm torque for normal driving and a little more horsepower for higher RPMs, if that is possible.  I am still couple of years away from installing my engine so I have time to consider other options. I do intend to install a 3.27 rear axle to reduce highway noise. I do not want to change from the original appearance.

Howard
71 280SL 4-speed

[DaveB]

I don't think there are any aftermarket versions but the european spec cam has a different grind for more hp. Or a 230sl cam may fit.

[Benz Dr.]

I used a 230SL cam as it's the closest to a euro 280 SL. I also advanced it up to 12 degrees for optimum performance.

[kampala]

Howard,

If you are serious about Cam Modification, contact Tom Colitt.    Tom has created specs to grind these cams for more performance.   I recently saw a 280 at a cars & coffee that Tom did this modification to and the owner was quite impressed with the power.  Here is one post about it, there are others.

https://www.sl113.org/forums/index.php?topic=16518.msg114357#msg114357