Help please. regarding head bolt re-torque event

[roymil]

Hello,  Today after reading instructions pretty carefully I started to re-torque the head bolts on my 280 since it hadn't been done while sitting in storage for 20yrs.  I warmed the engine, removed the valve cover and water cap.   #1 went as expected.  It loosened with about 100ft-lb of torque and then re tightened to 80 ft-lb with no issue.   #2 loosened the same, but when tightening it back up, just as the torque wrench clicked, I immediately heard and felt a second click and then it was loose.  I feared that the bolt sheared but when I pulled it out it was fine and clean with no sign of thread damage or evidence of metal shavings.   I put it back and it wont tighten.   Seems the issue must be on the thread side but I'm not sure what that end looks like.

I've removed #2 bolt and stopped until I can get some feedback and advice from the team here.   A bad thing happened I think, but I have no idea what?

Any help or ideas appreciated.
thanks much,
Mark

[Cees Klumper]

Did it perhaps shear off, and although what came out looks ok, the bottom section is still in the block?
The only way to tell would be to compare its length to an 'intact' one.
When you put it back in, does it at least thread in for a bit, but then just sort of spin without resistance?

[roymil]

I was hesitant to pull out another bolt to compare length, but see attached picture of the #2 head bolt.   It doesn't look to be damaged in any way, the tip looks as I'd expect, but I've not seen one before either.   I tried again and although it threads in fine, it just wont tighten.   It backs out fine, but still no sign of metal shavings I'd expect if it had damaged the threads in the block, and I just cant think of another reason it would spin.  It seems those threads have to be shot, but I'm holding out hope there could be another answer?    Again, I really appreciate any ideas here because I'm thinking the only way to figure it out is by pulling the head.   I'm wondering about shoving a bore scope in there next.   thanks, Mark

[Charles 230SL]

Mark, I've got a 230sl/M127 so I'm not familiar with 280sl head bolt variations but appears there's (2) different lengths of head bolts; 115mm and 145mm. Has the head ever been rebuilt? If so, is it possible #2 head bolt is 115mm when it should be 145mm? how long is your #2 head bolt?

https://www.sl113.org/forums/index.php?topic=22550.0

[roymil]

thanks! I think thats a clue.  This head had a valve job in early 90's.   I just measured the #2 bolt at 105mm.  It's the shorter of the two on the head.  It's suspicious that at some point the factory decided to add 10mm to these bolts.   One has to wonder if they realized the bolts weren't engaging enough threads for the higher head torque (80ft-lb) on the 130 block.   

Now I have to wonder if a potential solution for my situation is to try a 115mm?   What have I got to lose at this point?  Really, I don't know the downside.   My concern would be even if a longer bolt torqued up, that means it would only be holding by 1cm of threads, and thats assuming all below my current bolt is fine and thats hard to know.

So, sounds like even if I have to pull the head to fix this I need to procure the longer head bolt set (115 & 145mm)?   Has anyone done this swap?   On the other thread there was an open question if there was room for the longer bolts but I assume there must be.

Lastly wondering if anyone knows a US source for head bolts?  I checked my usual go-to places but only found head bolts at the SLShop, which has a fair price, just takes longer.

thanks for the ideas!  -Mark

[ejboyd5]

Sometimes too late we remember the adage, "If it ain't broke . . ."

[roymil]

Yes, believe me I've thought about that, but I'm also thinking that if it was that close to failure then it was really just a matter of time, and I'd sure prefer it to fail in my garage on a nice afternoon than on the road with a blown gasket and billowing smoke, or worse, a gradual failure that I don't detect until the bottom end is effected.   I knew the risk but I'm lucky, I have no permanent damage here.  This is fixable, and when I'm done I'll know I have the right length bolts, new gaskets, valve guides, etc.

It's all part of the fun with these things.  I'm actually looking forward to pulling the head and doing preventative maintenance. (but I wont be heartbroken if I just need a longer bolt ;-)

To that end, I found a series of pagoda notes on head rebuilds and wondering if anyone has specific tips or checklist of things to do while I'm in there?  performance mods?
thanks much for the helpful comments. - Mark

[Charles 230SL]

.... wondering if anyone knows a US source for head bolts?  I checked my usual go-to places but only found head bolts at the SLShop, which has a fair price, just takes longer...

Mike at Metric Motors quoted me a price of $120.00 + shipping for a set of M127 head bolts. Appears they keep head bolts in stock. Metric Motors is in Canoga Park, CA.

[Cees Klumper]

You can just order the specific type and lengths of bolts from McMaster-Carr for example, and 'experiment' with different lengths. You can measure the length of thread that will engage in the block by just inserting a longer bolt until it meets resistance (= the block threads) and then you'll know how much thread depth that length of bolt would need. Hope I am sufficiently clear.
But perhaps just ordering a complete set is a good idea, because now we worry about the remaining bolts ...
If you replace them one at a time, no need to pull the head?

[Leester]

I think the head bolts are M12 so you could try using anything that is less diameter than 12mm  and longer than 115mm (like a long Phillips head screw driver) just to see how deep the hole is. If it will take a 115mm bolt I'm sure I have one and would be happy to send it your way. Whether you buy one or more new ones, you could at least determine (1) if the longer bolt will fit and (2) if the longer bolt will bite.  Lee 

[roymil]

Thanks for the good ideas!   I'll plumb the hole tomorrow and measure depth.   It was already mentioned these are M12.  Can anyone confirm they are 1.75 mm pitch?   That seems closest to what I measure.  I'll see if I can find some different lengths locally in any low grade, just to fit check, and then I can be exactly sure of what will work.

[WRe]

Hi,
the M130 engines and associated cylinder heads were available in different versions, so that different cylinder head bolts were used. For example, starting with chassis number 16450, longer threaded bushings with longer screws (115/145mm) were used. You should therefore urgently check beforehand which variant you have in order to avoid tearing out the bushings or the screws sitting on (see workshop manual).
...WRe

[roymil]

Thank you for that info!   It's further complicated since I cant go by chassis number.  The engine in my 280 was rebuilt in the early 90's and is from a 280SE.  I did check the depth and there is ~119mm of room, so at least i know a 115mm bolt wont bottom out.   I will check the BBB before doing anything.  Also, i hope to get some advice from metric motors.  thanks all for the inputs, its really appreciated  -Mark

[roymil]

FYI, looks like Metric Motors is out of the parts business.  Just received this :

"Sorry but we are no longer in the business of selling the parts.
Due to time constraints, limited supply chain and the need of the parts for our own engine builds."
Regards, Mike
Metric Motors, Inc. ,MERCEDES-BENZ ENGINE SPECIALISTS

[Benz Dr.]

Which head bolt are you having trouble with? The cam bearing bolt or the one in between the cam bearings? 

[roymil]

It's the shorter one between the bearings.  It's the #2 bolt in the middle, passenger side.  It measures 105mm but I understand sometime in production these were changed to 115mm.   This is a rebuilt M130-980 280SE block (#6247) and it should be the early style "square" head but I don't know if that bolt length change to 115mm is correlated with the "oval" head change.   I did measure the hole depth at 119mm so there should be room, unless there is some other reason not to have a longer bolt, per WRe's comment above I was a bit concerned.  appreciate any thoughts or advice. thanks, Mark

[Benz Dr.]

You should have the early engine. The late engine has slightly longer head bolts but I don't think this is your problem.

Prepare to remove your cylinder head. Sounds like the threads are pulled in the block. Turn your engine over to TDC number one cylinder before you start removal.

I run a tap through all of the threaded holes in the block to remove rust and dirt. I also clean all of the screws before any of them go back into the block. This sort of attention to detail will result in great returns while doing assembly. A broken oil pan screw can be expensive to repair once broken off so use a bit of heat if they won't move.   

[roymil]

Yes, this is the conclusion I've come to as well.   I fished around in the hole with a magnet and picked up quite a bit of metal, but interestingly, none of it was from fresh thread damage, (sharp silver curved bits).  it was all quite small gritty chunks caked in oily grime.  Clearly not freshly damaged thread material.  I know, Ive messed up enough threads in life.  This really seems to be old corrosion damage, or corrosion that happened after threads were messed up during the rebuild in the 90's.   

So, my thought is that during its 20year improperly stored sleep, some liquids became acidic, probably coolant, and attacked the metals in the head.   I need to see what other issues are there.  I know the water pump vanes were almost completely missing from corrosion when I changed it.   I don't see how the head would have escaped this sort of corrosion, so it makes sense to deal with it properly now.  I'm kind of thankful to find out this way, with no overheating, blown gasket, or other nasty catastrophic damage. 

Has anyone experience with using Time-Serts for this type of thread repair on the head?   I've used them for a spark plug repair and was amazed at the better-than-new result.  When I pull the head I'm putting Time-Serts in the other 5 spark plugs and if it goes as I hope, I'll do all of the head bolt holes if they appear to have been corroded as well.

time to TDC#1 and break out the tools.  Thanks for the help!

[ja17]

I'll check to see if I have some 115mm bolt if you like.

[roymil]

I just received some today, actually 120mm which I just now cutoff to 115 and dressed up.  Now I have some extras too if anyone should ever need.   I sure appreciate the offer though!   And also many thanks to you Joe for of all your comments in that pagoda notes "cylinder head tour".  I've been reading it very carefully in case I do have to pull the head.

My plan tomorrow is to properly chase and clean the threads that are left below where the old 105mm bolt reached and then try to see if a 115mm will torque up.   if that works, I realized its only a temporary solution, but I want to try because everything else is in pretty good shape.   -Mark

[roymil]

I'm really happy to report that the 115mm replacement head bolt worked great!   It engaged the good threads that were down below where the old 105mm head bolt had reached and it torqued up to 72 ft-lb. (the cold spec)

Before I installed it, I thoroughly cleaned out the hole with a strong magnet and found that except for one partial ringlet of freshly pulled thread, the rest I would have expected to find simply were not there.  There was only a relatively small amount of obviously old and small oily metal bits that had to have been there a long while.   I even bought a new borescope to run in there and it showed a clean hole with good threads at the bottom.   I've come to the conclusion that this rebuilt block must have had the hole damaged before or during the original work and it wasn't noticed at reassembly since it did torque up.  Apparently it was hanging on 1 or 2 threads all this time.  When I re-torqued I pulled what was left.

There's no way to know the condition of the other bolts and block threads without pulling and inspecting, but I've decided not to for now.   All the plugs have good color, compression is like new, leak down is fine, and theres never any smoke.  I plan to monitor oil and water quite often and if it ever looks like my gasket is giving out I'll pull the head then. 

thanks for the help and advice during this little detour!