Head rebuld - cam alignment

[rumb]

Hi ya'll, I've been reading here for some time, but have not ever posted. I am rebuilding the engine in my 67 250S, M108.920 which is pretty much the same engine in your SL's and you guys seem to have the best technical knowledge. I've always hoped to get an Pagoda someday, but am currently restoring a 6.9.  I have already read up on any posts here already regarding my issue.  I have already rebuilt the short block with new pistons and bearing.  The head is now in need of work. This head was rebuilt 40-80K miles ago, I had it done @35 years ago but my recorded mileage doesnt make sense to me so I am not exactly sure how many miles.  There were +100K when it was done the first time. +100K on original block, then I put a factory short block in and drove another +100K miles.  I am putting back in the original block that I have lugged around for 35+ years now. My dad bought this car new and I have driven it for 42 years now.

The rocker stud balls are worn @1.5 mm and show the little nub on top.  I have new ball studs and rocker arms. There is at least one valve that I was no longer able to adjust due to wear. All of the old ball studs show only about 1 thread left.

The head thickness rough measures 84.13   84.59    83.95 on one side and  84.17     84.56   84.20 on the other side.  The bottom surface is maybe .15mm out of flat, so it is pretty close. I think I read the spec is .1mm?   From the thickness measurements the top is curved. This is obvious as I cant turn the cam very easy at all.  The cam bearing journals quick measurement seem to be .5mm out of round, is this out of spec?  I would guess so.  I did find a new set of them I can get if needed.

Since the valve lash is currently nearly un-adjustable, I need to figure out the correct steps to get it into spec. It appears that the cam is capable of actually (slightly) bending on each revolution when forced to! It is currently quite stiff to turn and as mentioned the cam towers appear to be worn. I guess the shop that did the head the first time didn't catch that and I was quite young and didn't know the difference.

This is what I think needs done, your advice is welcome.

Mill bottom of head flat removing .15mm
mill top of head flat removing @.5mm (based on measurements above)
new valve guides since the old ones have to be removed anyway
replace valve seats and valves with new ones to restore sunken valves +.5 to 1mm?
grind end of valve stems .5 to .75mm
make cam tower shims of @1mm (take final head thickness and subtract from 85mm factory height)  based on measurements I should have 84mm head thickness when done. I assume the only source of these is to make them.
replace cam towers?
install 2.5mm valve shims instead of factory 4.5mm.

I need to compensate for the already worn ball studs 1.5mm and the 1mm head thickness and the .5+ valve seat wear.  If I do everything above I can gain around +4mm which would hopefully give an extra 1-2mm of adjustment.

Comment?  Suggestions?

Thanks!

[ja17]

Sounds like you have a good plan. Be aware that you can gain some adjustment by using thinner contact pads under the rocker end. Looks like your below min. thickness in one place however. You might see if the head could be straightened a bit to save from cutting more thickness. May not be possible since  your warpage is not that bad. Lots of expense and time replacing all the valve seats. You might want to consult your machinist and check the factory specs on the valve seats. All new valves would be less expensive and may gain some more room on the adjustment end along with the thinner contact pads.

[rumb]

Looking around I can get 1/16" = 1.58mm extruded aluminum bar stock to make shims out of.  Do you think that this is flat enough and is this too thick?  I think that I will be using an offset key on the cam already. As long as the the timing marks line up everything should be OK?

I re-measured my cam towers and they are only a few thou out of round so it looks like I can use them.

Any chance someone has the specs on valve seat depth?

[Benz Dr.]

You can buy ready made cam bearing shims so I wouldn't bother trying to make them. I use one or sometimes two pieces ( .015'' ) under each bearing depending on how much material was removed from the head or block.

[rumb]

Dr. Benz,  do you have a source for shims I can contact? or a part number?

Thanks!

[Benz Dr.]

Sure. Contact Metrics in CA.

[rumb]

I have the head at the machine shop and it is going well now.  They at first could not remove the ball stud bases, but manage to remove all without tearing any threads.

New question, they removed 3 @5/8" dia oil plugs from the block, I see that 2 go on the rear of the block, but cannot find where the third one goes. Anyone know where they go?

Thanks!

[ja17]

One is
 behind the chain sprocket on the front of the block.

[rumb]

Thank you!  I obviously missed that.

[rumb]

Finally found it! It is behind the lower chain guide. Removal of the pin with the large nut, the 2nd pin and then the guide finally revealed the location. The reason for the large nut pin is to access the plug behind it. I also noticed that the lower plug in the back lines up with a galley that run to the front of the block. The upper rear plug galley goes thru to behind the pressure relief valve.   

[Tyler S]

Just an FYI, You will most likely not need an offset cam key if you are replacing the timing chain and are using the cam tower shims. Though you still may need the thinner 3.5mm valve lash caps.

[Benz Dr.]

Possibly. A .015'' cam shim will raise the rocker arm position quite a bit and I don't think it's a one to one ratio - it may be more. When we refer to rocker arm geometry this what we are pointing to.

[stickandrudderman]

Fitting offset woodruff keys in the cam gear is a waste of time. There is ample valve clearance and you will not notice any difference in performance. Just get the timing marks as close as you can but make sure that any discrepancy is left to the retarded side (so cam timing is behind)
Believe me, I’ve spent hours with degree discs and DTIs getting it spot on and there is absolutely no discernible difference.

[ja17]

Good advice Stickandrudderman on those offset keys!

[rumb]

Hi all,
Progress on my engine has been delayed due to other parts of life. I do have my head back from re-builders now.

I found a used oring that I dont know where it goes. I also found a similar sized new one in the head gasket set. See picture.  Can anyone tell me where this oring goes? The old one is oily if that helps.

Thanks!

[mbzse]

.../...Can anyone tell me where this o-ring goes?.../...

Looks like seal ring for cam chain tensioner

[rumb]

Thanks!!!!

[Benz Dr.]

Don't grind the ends of your valve stems for any reason. We use cam shims or shorter lash caps to correct rocker geometry.

[Sead]

Sure. Contact Metrics in CA.

Hello,
ist there a source for those shims in Europe?

Regards
Sead

[Pawel66]

I just had them made in a machine shop. Took the pedestals to them and just, if I remember correctly, briefed wher the oil channels are that you need to be careful about.

[Benz Dr.]

Don't bother messing around with making cam shims. There are several different thicknesses to choose from and they're not expensive.

If you have a flat parting surface but your thickness measurements are all over the place, you should probably have the top of your head milled. Make all of these determinations BEFORE you do any other head work. Everything from the top of the head needs to be removed including valve guides, studs, dowel pins, and the threaded cover caps. If you already installed new valve guides you will need to remove them and may even need to replace them if they get damaged. Don't be that guy.   

[rumb]

An update and big thanks to this group. I have finally reassembled engine and set to reinstall shortly.

[rumb]

One more

[Tyler S]

Looking great! It is always nice when you can see the finish line in sight.