1991 350SDL Timing Issue

[oilslick]

A friend of mine has been in the process of replacing the head gasket on his 350SDL. He had the head shaved 6 thousandths and reinstalled it. He told me that if he lines up the cam marks then the crank is at 5* ATDC. If he lines up the crank then the cam marks are noticeably off. I went and verified this myself. He installed a new chain and tensioner. Now it’s only 3* ATDC, but still off from what he told me. I haven’t verified it this time.

Could the shaving of 6 thousandths off the head be the problem? Would a thicker head gasket be the solution? I’ve replaced head gaskets on enough of these MB diesels to know how to set the cam and crank timing, but everything I tried yielded 5* ATDC. Any words of wisdom?

[torsionbar]

How about the IP? The crank and cam are only part of the timing equation.

[oilslick]

He removed the IP so it could be resealed. I loaned him a timing basket to use while the IP was missing. Even with the IP removed, he should be able to set the valve timing.

[dieselbenz1]

All I know is a standard gasket is 1.74 mm thick.
The thicker gasket is 1.94 mm.
.152 mm was shaved off.
The tensioner needs oil pressure to apply pressure.

[tjts1]

Originally Posted by dieselbenz1

All I know is a standard gasket is 1.74 mm thick.
The thicker gasket is 1.94 mm.
.152 mm was shaved off.
The tensioner needs oil pressure to apply pressure.

The tensioner has a spring. It doesn't need any oil pressure to set timing.

[Maxbumpo]

Originally Posted by dieselbenz1

All I know is a standard gasket is 1.74 mm thick.
The thicker gasket is 1.94 mm.
.152 mm was shaved off.

This is probably the issue. If material was removed, then a thicker gasket must be used to restore the original dimension between the crankshaft and the camshaft.

Another possibility is that the crankshaft position pointer on the front of the timing case is not calibrated.

I'd say that if his timing is off by only 3 degrees, leave well enough alone and motor on. He could see if the pointer is calibrated using a working fluid in a clear tube, that fills the pre-chamber and the cylinder, and determining top dead center by watching the rise and fall of the fluid. If 3 degrees off is not acceptable, the head needs to come back off and more material removed so that with the thicker size gasket (if it is even available) the correct height is restored.

[dieselbenz1]

I measured my cam sprocket at 110mm. Therefore circumference is 345.4mm. 360 degrees / 345.4 mm is 1.04 mm per degree. .152mm x 2 = .304mm total chain length longer. 1.04 mm / deg multiplied by .304 mm equates to 3 degrees retarted due to head shaved off .152mm.

Hopefully someone will validate my math and thinking.

[dieselbenz1]

Offset key Part #: 621-991-02-67-M22 will correct it.

[Diseasel300]

Unless the 3.5L engine was different, the OM60x engines don't use keys in the camshaft sprocket, they are indexed by a dowel rod projecting from the camshaft. There is no offset key available to correct timing like the OM61x was.

[dieselbenz1]

I see the dowel pin on the fsm hmmm guess peach have the off set key compatibility wrong.
Has me wondering now if one just has to live with it should a head be shaved a different amount than the repair head gasket size.

[Diseasel300]

Pelican and most of the other vendors show the offset key all the way through 1994. I suspect some supplier has wrong info and they just go with it. Would suck to buy the key and then find there's nowhere to put it.

The FSM gives a maximum depth for skimming, which corresponds to the repair gasket thickness. If the repair gasket can't be sourced, living with the timing being slightly off is the only real answer as there's no other way to correct it.

[dieselbenz1]

Diseasel300 when you had your head refurbished was it skimmed?

[Diseasel300]

Mine wasn't skimmed. The warpage was well within limit and the surface was still in good condition and pit-free. I got lucky.