OM617 Head Bolts - PeachParts Mercedes-Benz Forum

pilot53 · #1 12-07-2019, 08:31 PM

Can you reuse head bolts on an OM617? Looking at new bolt prices, its several hundred $$.

ROLLGUY · #2 12-08-2019, 12:13 AM

Quote:

Originally Posted by pilot53

Can you reuse head bolts on an OM617? Looking at new bolt prices, its several hundred $$.

Some say yes, most say no. Being stretch bolts, they should be replaced. However, there is a specific measurement for them to be within spec, and I don't know what that is. My feeling is that it is NOT worth the risk of a bolt loosing it's tension. Having two torque values, and two 90 degree turns on each bolt, you won't know that one (or all of them) is out of spec until it is too late if they are not known to be in spec before starting the torque sequence.

Alex E · #3 12-08-2019, 02:56 AM

I reused my head bolts.
The acceptable measurement length is in the FSM, my used bolts were as new spec wise.
When I reinstalled the head it was scary as Hell doing the final 90° tightening as I thought no way... they're gonna bust. That's how tight they got to go.
So, look up the measurement specifications of acceptable length and that will determine if you need to purchase new bolts. If they aren't perfect get new.

ROLLGUY · #4 12-08-2019, 10:07 AM

Quote:

Originally Posted by 5cylinder

...........

Depending upon which bolt size is specified, OEM cost not from M-B ranges from US $2-$3 each. From M-B, cost ranges from US $5-$28 each.

https://www.pelicanparts.com/catalog/SuperCat/3390/MBZ_3390_ENGCYL_pg2.htm#item10

From our sponsor it is only $67.75 + shipping and tax for all 22 bolts. For me that is cheap insurance. I will never install a used head bolt ever again. The washers can be used over and over. Be sure to oil the threads and washer.

BillGrissom · #5 12-08-2019, 10:49 AM

I will reuse mine if I ever finish rebuilding my 1985 OM617 engine. I did a gasket change on my 1996 Plymouth 2.4L engine which has "torque to yield" head bolts and the manual says to use new ones. I figured I could just yield them a little more. That was 18 yrs and 120k miles ago (now 230K) and no leaks since and still perfect compression. The OE gasket had a strange problem where it leaked oil to the outside, the fix being a PN change to multi-layer-steel gasket.

I think the difference is more from assembly. I think "torque-to-yield" definition is that you snug them to a certain torque, then mark the head and turn a fixed angle (say 3/4 turn). If you know metallurgy, tough metal like in bolts increases in tension as it yields until the diameter starts to neck down appreciably. That is why the main criteria is the diameter of the bolt. Head bolts are so long that it might be hard to locate the min diameter, so they spec a length stretch. As I recall, the short flex-plate bolts are spec'ed for a diameter neck-down, to allow reuse. But, don't quote me, just speculating, and I never want nervous-nellies following me in things like silicone brake fluid, waterless coolant, HC refrigerant, and ignoring much of the M-B FSM special-tools and methods.

pilot53 · #6 12-09-2019, 04:50 PM

Quote:

Originally Posted by ROLLGUY

https://www.pelicanparts.com/catalog/SuperCat/3390/MBZ_3390_ENGCYL_pg2.htm#item10

From our sponsor it is only $67.75 + shipping and tax for all 22 bolts. For me that is cheap insurance. I will never install a used head bolt ever again. The washers can be used over and over. Be sure to oil the threads and washer.

Do you mean for aftermarket bolts? For genuine mb bolts just the 5 100mm bolts its $171.25, then another $65 for the 120mm, and 8 140mm that are nla.

What brand can I trust with head bolts? I would gladly just replace them if it were only $67.75.

ROLLGUY · #7 12-09-2019, 06:08 PM

Quote:

Originally Posted by pilot53

Do you mean for aftermarket bolts? For genuine mb bolts just the 5 100mm bolts its $171.25, then another $65 for the 120mm, and 8 140mm that are nla.

What brand can I trust with head bolts? I would gladly just replace them if it were only $67.75.

I have used the bolts from our sponsor (V.R.) many times, and never a problem.

barry12345 · #8 12-09-2019, 07:00 PM

I think that if a stretch bolt has not elongated at all. It has recovered the stretch it produced when in service. It is not damaged. Any elongation remaining evident means that it has not and should not be reused. You are too likely to work it into the true over yield area. With the engine in service. Mercedes gives a tolerance yet for this to be really valid the material those bolt where made from would have to be kept to a very tight standard. Especially for a cast iron head.

Buy a known good brand of aftermarket bolts. I think engine builders where forced to go to variable pressure bolts in service. Because of the expansion and contraction coefficients with aluminium heads. I think this is far less critical on cast iron heads.

In the grand scheme of things I would use new at 67.00 a set. At hundreds of dollars a set I would have to think about it. For a cast Iron head I would be less concerned. If they show no evidence of retained stretch they go back in. As there is then no evidence of distortion.

jsp300D · #9 12-19-2019, 03:53 PM

Just go buy new one, peace of mind and not that huge of a price.

5cylinder · #10 12-19-2019, 04:06 PM

Quote:

Originally Posted by jsp300D

Just go buy new one, peace of mind and not that huge of a price.

LOL.
After 19 years and 231,000 miles, the power steering pump on my first W123 failed. A replacement was $200-something dollars. I bitterly complained to my parts guy about the outrageous price. His response? $200-something divided by 19 years is...yeah well. I chose to stop whining and replaced the pump.

Dan Stokes · #11 12-20-2019, 04:44 PM

Another option on the head bolts: Get the dimensions (diameter, pitch, length, etc.) and contact ARP for a set of non-torque to yield bolts. ARP bolts are way beyond aircraft quality. I installed a set in my Ford V6 (3.8L IIRC) in a Windstar and put an end to the constant head gasket failures. Torque the head, warm the engine, retorque, and drive it.

Dan

t walgamuth · #12 12-21-2019, 07:37 AM

The torque stretching bolts are made that way because it is a more reliable and accurate way to get the clamping force needed for good service. The book specifies dimensions to be checked for stretch. Have your machinist do that and you should be fine if they meet the spec.

Of course if you want new bolts you cannot go wrong that way.

Dan Stokes · #13 12-21-2019, 11:00 AM

Quote:

Originally Posted by t walgamuth

The torque stretching bolts are made that way because it is a more reliable and accurate way to get the clamping force needed for good service. The book specifies dimensions to be checked for stretch. Have your machinist do that and you should be fine if they meet the spec.

Of course if you want new bolts you cannot go wrong that way.

I fully understand the theory behind the TTY bolts. But I also know that in practice engines with TTY head bolts tend to lose head gaskets, some more than others. The OM617s seem to hold up really well while the Ford 3.8s lost head gaskets right and left (literally - they're a V engine).

My explanation is that TTY bolts experience cycling thru thermal excursions and those cycles eventually elongate the bolts slightly which relaxes the clamping force. I'll admit up front that I haven't done any research on this but this is where my Einstein-like thought experiments take me. Because the ARPs solved the gasket failures on my Ford 3.8 I can add some experimental data though admittedly with a sample size of 1.

All in all, I'd say either TTY or tough conventional bolts can work and if I was replacing the head bolts on Mutt I'd go with ARP studs because it's a race engine now and I can reuse the ARPs indefinitely. If Mercedes wants stupid money for a set of head bolts ARPs are at least worth considering.

Dan

t walgamuth · #14 12-21-2019, 11:21 AM

Are the arp bolts more or less expensive than the Mb bolts?

Yeah, on a race engine studs are the way to go.

Dan Stokes · #15 12-22-2019, 11:39 AM

You would have to contact ARP as far as price. IIRC I spent under $200 for the ARPs for the Ford - a bargain given that it stopped the head gasket leaks.

BTW - Just because ARP dowsn't list s kit for any given application doesn't mean they don't have the bolts. Send them the dimensions and they'll put a set together for you.

Dab