I replaced the stretch bolts for non stretch metric m12 allens on my m104. After some thought, I dont think it would be wise to use the same torque specs for the stretch bolts that call for 55 N-m followed by a 2 additional 90 degree turns.

After some reading of various other engines, I have came to the conclusion of a reasonable figure of 70ft lbs followed by an aditional 10ft lbs after the engine has been cycled for 500 miles. but this is total guess work!

Does anyone here have a torque figure that can calculate the difference in head bolt torque between OEM stretch bolts and aftermarket non stretch?

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Where are you using them - head bolts, flywheel?

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Jim

Ya, they are cylinder head bolts, sorry. Should of mentioned it. m12 I think stands for Metric 12mm. IIRC they are 12.9 grade.

With the flywheel bolts, I just went with new standard stretch bolts.

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Why the change? Why not use the proper fasteners?

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Jim

piece of mind has something to do with it. from what I have read, the introduction of stretch bolts eliminates the need of re-torquing the cylinder head down after 500 miles of heat cycles. As every engine that has stretch bolts.. is a mass produced engine.

now that the m104 is in my hands, I really dont mind opening up my valve cover and re-torquing the head bolts as some have done in the past.

most people just re-use the stretch bolts if they are within spec. which I think mine were still good, but this is my first time rebuilding a motor and I just thought the stretch bolt was a head ache.

ARP studs have also been mentioned, and the sound nice, but not for this m104, at least not yet. =)

also... I figured since I was buying new head bolts anyways... for the same price, I would buy non stretch so I dont have to worry about buying new ones ever again.. as I am sure, that I will be taking the cylinder head off again in the future for whatever reasons.....

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Just out of curiosity, do you think fasteners that you have to go in there and torque are better than stretch bolts that you don't have to mess with? I have never really had any issues with the stretch bolts and have re-used them. Never have used ARP studs. Are they an improvement? I don't have any experience deviating from oem head bolts.

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Jim

I have heard a story of cylinder head floating on top of the engine block in a high performance application with forced air. The thought of that + stretch bolts = sad face lol

The 3.2 m104 is for a 1992 190e, and I also have a 717.411 and 717.432 5spds, LSD, Megasquirt 2 v3, and a holset HX40. and I have a mindset of 350 moddest rwhp out of my setup with 10lbs of boost.. and with alcohol injection 400-450rwhp goals. 10-20lbs of boost should be reasonable.

The OEM stretch bolts... may do the job...

Serious engine builders use crazy fancy fasteners and they are not stretch spec. There is a youtube video of a mechanic using ARP and some fancy measuring devices to check the load of the bolts with the use of oil additives for the threads and yeiled a few different results.

Things start to get a little more critical at this point.

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Thanks for the explanation. Some of the automobile shows where they build engines up seem to always use ARP fasteners. It would be interesting to see if they have some for Mercedes application.

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Jim

Good info in their catalog:

ARP-bolts.com | ARP Quick Catalog Viewer

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Jim

I forgot about my original post for head bolts..

thread can be found here, reguarding various m102 m103 and m104 engines

stretch bolts modification - 190 Revolution

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thanks

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Jim