I will be doing a head gasket on my 90 300E 2.6 shortly. I was talking with a friend of mine. He said that they make a specific lube for head bolt. I have heard many ways of installing the head bolts. This is the first I have heard of a specific lube for head bolts. Any help?

Never heard of using any lube on the head bolts. They have a very specific torquing procedure and as they are "strech" bolts, not sure if the lube would interfere.

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Just lube it with engine oil LIGHTLY.

What brand head gasket are you using?

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Actually the torque spec is for dry bolts. Lube them and you will overtorque and probably break them.

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+1 on no lube!

As always a picture is worth???

Always oil the threads with lightweight engine oil.

Attached Files

4050 - Examination and tightening of the cylinder head bolts Engine 104.pdf (46.5 KB, 284 views)

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Maybe a distinction without a difference but isn't the OP's 1990 300E 2.6 a 103 engine not a 104.

same procedure

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Yep. Lightly oil the threads and the bottom of the bolt head - the surface of the bolt that comes in contact with the cyl. head - it's all in the service manual.

Without the lubrication, the threads will end up galling.

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The light oil is the way I knew of, I had also heard dry. Never heard of a lube till my buddy told me. Seemed a bit odd to me also

Well that settles it. I had checked on my M113 and didn't see any requirement so assumed (yes, I know ) ...

It is an important distinction, though, since wet torque reuiremnts can be up to 30% less (see http://www.tpub.com/content/bridges/TM-55-1945-205-24-4/css/TM-55-1945-205-24-4_742.htm ).

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Just to answer the question if others are looking. There is a specific lube for Head bolts made by ARP. I ended up selling the car before doing the head job but used the product on a Rover when I did the head job.

actually, it's arp not apr. they are famous for their rod bolts, nuts and head bolt stud kits for racing. good luck, chuck.

I read through this thread and see that only the last few are current, the rest are pretty old. On the older engines, 102, 103, 104, you just use engine oil. I would dip them in clean engine oil them lay them on a shop towel to allow the excess to run off/soak off. First measure the length to make sure they are not overstretched, then I'd run a die over the threads and also run a tap through the holes in the block by hand, to make sure they were all in good shape. Then make sure the bolt holes were all clean, I'd use brake clean then shoot compressed air into the holes to make sure all the gunk was out.

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Just an additional comment: the M103 factory manual states to oil the threads and under the head of the bolts, but states no particular oil to use. So we could assume any light engine oil I guess. If the underside of the bolt head is left dry, It will gall the aluminum head surface - I know from experience.
Friction in the threaded area is probably not as critical in a torque-to-yield bolt as used here. The thread friction would affect the initial measured torque value, but it's only 50 lb-ft here. Then the major force is done by the 180-degree additional turn, which wouldn't be affected much by any additional thread resistance, since the stretch occurs on the bolt shank, not so much in the thread area. Anyway, clean threads and lubricant are the way to go, per the manual.

ARP does recommend a special lube for their torque-to-final-spec bolts, but they use specific final torque values and don't specify torque-to-yield measured-turn-angle procedures that MB specifies.
DG