Head Bolt Mystery / 300D - PeachParts Mercedes-Benz Forum

Fitts07 · #1 06-03-2016, 09:32 PM

Hello all,

I recently acquired a 1979 300D. Its in great shape but the head gasket was blown (lots and lots of oil in coolant). I had the head milled and rebuilt. The block was verified straight. I am now ready to begin reassembly.

I apologize if this has been discussed, I searched but couldn't find anything.

So, in FEB of 1979 Mercedes changed the head bolt style and torque sequence for the OM617. Mercedes also shortened the head bolts by 1mm and cut deeper bolt holes in the block by 1mm. My car has a build date of SEP of 1978, so it has the old style head bolts. Or so it should.... When I removed the head it had a mix of new and old style bolts, which in the FSM is strictly forbidden, and is possibly part of the reason the head gasket blew. Along with the fact the head was warped.

The old style are HEX head bolts and the newer style are 12 point stretch bolts.

I would like to purchase all new bolts to put the head back on. Problem is the old style HEX heads are no longer available. In the FSM it states that if the engine originally came with HEX bolts it should be reassembled with them and vice versa for the 12 point.

So does anyone know if it is okay to replace all 22 head bolts with the new style that is still available? If I do that which torque sequence should be used? Are there any other things I should change or inspect when swapping to newer bolts, I.E. thicker washers?

Build Date 9/78
Engine # 617.912.12.056508
Chassis 123-130-12.111381

Thank you!

leathermang · #2 06-03-2016, 09:39 PM

Was that correct in your description that they shortened the prescribed bolts AND made the hole deeper ?

Fitts07 · #3 06-03-2016, 10:53 PM

Yes, I'm 98% sure. In the morning I'll check the FSM again. I think with the stretch bolts you give it something like 2 ninety degree turns after the final torque. The 2mm of extra space is to accommodate the stretch I presume.

jt20 · #4 06-03-2016, 10:53 PM

I think leathermang is on the right track.

You need to be certain (eg. abso fkn lutely certain) that the depths in the block were modified.

If that is the case, you will have to drill and tap farther into the block. (sorry I can't be of more help, i have not seen that mentioned.)

On top of that, you should be using the updated bolts and newer style headgasket - not only because they are what is available, but because they are superior.

Fitts07 · #5 06-03-2016, 10:57 PM

Jt20, makes perfect sense. I did purchase the most up to date non-turbo head gasket mercedes sells, their older ones have been superceded.

I wonder if instead of drilling and tapping, which I'd really rather not do, I could use thicker washers?

jt20 · #6 06-03-2016, 10:58 PM

I have to admit, I would try to cheat.

I would do the math on elongation / deformation and estimate how much the bolts would 'stretch'.

Along with some real world measurements of putting the new bolts into the block and measuring where they 'bottom out'.

It would be a comparative estimation that lead to an educated guess which ultimately culminated in a fantastic gamble.

...or you could just drill and tap them to be safe.

jt20 · #7 06-03-2016, 10:59 PM

Quote:

Originally Posted by Fitts07

Jt20, makes perfect sense. I did purchase the most up to date non-turbo head gasket mercedes sells, their older ones have been superceded.

I wonder if instead of drilling and tapping, which I'd really rather not do, I could use thicker washers?

I am an overcomplicated dolt.

that is a brilliant and simple solution. thicker washers. make sure they are hard enough and wide enough.

perfect solution.

try to get some measurements first.

nice work!

leathermang · #8 06-03-2016, 11:07 PM

I think you can use the later type of bolt ...and agree they all need to be of the same type. As long as they are not too long....
It is very very important that the holes you stick the bolts into are CLEAN and lightly oiled... that is standard machining procedure for accurate torquing ... which is only an estimate of the ' pull down force' on the head. So you will want to run a tap through it before installing the head. If you can find a spiral gun tap of the correct size you can put a plug of wax in it and it will push out and capture dirt and junk.

leathermang · #9 06-03-2016, 11:07 PM

Ok...as to the washers... they must be Grade 8 ......

Fitts07 · #10 06-03-2016, 11:08 PM

:

Well I guess that pretty much sums it up then. I'll get the new bolts on order. I believe I saw 1mm thicker head washers on one of the parts websites too. Now it makes perfect sense lol. When they come in I'll get my calipers out and get to measuring to be sure.

Thanks!

Stretch · #11 06-03-2016, 11:36 PM

As far as I can tell those washers are sold for a different reason.

Mercedes seem to have "standarised" the length of the bolts made so fewer bolts of different lengths are supplied from the dealership. They are now selling a spacer to accommodate the extra length of the new bolts.

Here's the part number for the spacer 1020160376

http://www.peachparts.com/shopforum/3324316-post466.html

I'm pretty sure that's the number you need - for your OM617 too - but please check before buying

Also I think there's a section in WIS about the problem of the hex head bolts not being available any more. (Sorry but I don't have access to it at the moment so I can't check for you - if you have a friendly mechanic at the dealership now is the time to go and visit)

Fitts07 · #12 06-04-2016, 09:02 AM

In the event the new bolts are too long, can yall see an issue with using the new spacer and the original washers?

97 SL320 · #13 06-04-2016, 09:25 AM

Before you go too far, define "blown head gasket".

The only way to get oil in coolant from a head gasket is for the cylinder head oil feed to leak to coolant. Be sure to carefully inspect the gasket for a path otherwise you are not fixing the problem. Pressurized oil leaking into coolant through a head gasket is rare for most motors, not sure on the one in question.

As for bolt length, as long as the torque specs are the same between both bolts, I'd grind the ends shorter to prevent bottoming out in the block.

DeliveryValve · #14 06-04-2016, 10:02 AM

Quote:

Originally Posted by Fitts07

..........I would like to purchase all new bolts to put the head back on. Problem is the old style HEX heads are no longer available. In the FSM it states that if the engine originally came with HEX bolts it should be reassembled with them and vice versa for the 12 point.....

If you have the time, ARP bolts can make a custom HEX/non TTY set of bolts for you. Contact them for details.
The Official ARP Web Site | Contact Us

.

Fitts07 · #15 06-04-2016, 12:06 PM

Quote:

Originally Posted by 97 SL320

Before you go too far, define "blown head gasket".

The only way to get oil in coolant from a head gasket is for the cylinder head oil feed to leak to coolant. Be sure to carefully inspect the gasket for a path otherwise you are not fixing the problem. Pressurized oil leaking into coolant through a head gasket is rare for most motors, not sure on the one in question.

As for bolt length, as long as the torque specs are the same between both bolts, I'd grind the ends shorter to prevent bottoming out in the block.

Well, I had large amounts of oil in the coolant. There were signs of external coolant leak at the head gasket, and the previous owner had punched out the thermostat. I had the head checked and it was warped 4 thousands out. I didn't see any obvious signs on where the leak was at. No coolant in cylinders or coolant in oil. No smoke. The small narrow passage between cylinder 1 and 2 was blocked and had made a large indentation in the head gasket. I'll take a picture when I get home.