Camshaft

[declanobrien]

I am rebuilding my 280SL 1970 engine.I think at this stage I could do a thesis on head restoration. I am trying to salvage the original head which was machined down to 82.5 mm in places. It had also bowed in the centre. I will hopefully write up a full report to the forum when complete.
I am having difficulty with the cam installation. Due to the bowing of the head, I have shimmed the pedestals, each requiring different shim thicknesses. After many trial fittings of the head, using an old gasket, I can just about turn the cam by hand, when the head is torqued down. However, when I unbolt the head, the cam binds, as if the releasing of the head bolt pressure affects the alignment of the pedestals. How critical is the cam pedestal alignment? Should the cam turn freely when the head is off the block? as I am finding that the torquing of the head bolts affects the alignment.
Any advice appreciated.

Declan
 

[steves sl]

Call Tim Kidder at K&K Manufacturing, they sell body sheet metal. I talked to him several months ago about my cylinder head, he told me that, he can or knows someone that can straighten a head. The web site is www.kkmfg.com, I decided to wait until I finish the body repairs on my 230sl, before starting the engine repairs. Hope that helps.

[ja17]

Hello Declan,

If the cam is binding too much, a cam bearing (holder) may overheat and seize from the stress. Your goal should be to be able to turn the large cam sprocket by hand when the head is torqued down. You can have fair amount of resistance, but the easier the better. I would not worry too much about the resistance when the head is off. Be sure not to close off the oil passage in the front cam support with the shims. Oil from the block flows around  the front head bolt, up through the head and into the front cam support to lubricate the whole valve train and camshaft. Also be sure to pre-lube the cam assembly before final assembly. You may want to go through a couple quick warm up cycles with the cam before going on a long drive. This will help the cam run in with the new configuration.

Take a compression check as soon as possible. An over-milled head like yours could have too much compression on the end cylinders causing other running problems.

[declanobrien]

Once again thanks for this great info.
I finished the bottom end today, so next big job is fitting the head. Had a slight binding problem with one of the big end shells, which I traced to the bearing cap. All checked out with plastiguage. I did check each combustion chamber, and ground out some metal from nr 6, as it was 1cc lower volume than the rest. All now read 39cc.
The crankshaft turns  (using a ring spanner on the crank bolt) with all 6 pistons in place.There is reasonable resistance which I think is caused by the friction of the rings. The crank turned very easily before the pistons were fitted.
I think I will torque up the head bolts before I tighten the 4 nuts which hold the cam pedestals, as I would prefer the head bolts to set the cam supports without interferance from any effect  the small nuts might have, if they were tightened first.
Declan

[ja17]

Hello  Declan,

Yes, definitely use the head bolts to check the camshaft rotation. The four little nuts holding the holders in place are basically  just decoration.  The head bolts do the real work of holding the cam secure and true. Also leave the rocker arms off until the head is torqued down. This will allow you to check everything for ease of rotation and will lessen the danger of damaging the cam or a valve until all is secure.