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It sounds insane, maybe just crazy enough to work (Head bolt thread repair)


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RandomOriginalName
New User

Aug 21, 2015, 5:38 PM

Post #1 of 6 (1703 views)
It sounds insane, maybe just crazy enough to work (Head bolt thread repair) Sign In

1985 Mercedes 380SL (R107) 3.8L v8 m116 engine, 195k miles with a broken clock (probably around 210k by now) Aluminum block

Tl;dr at bottom

A while ago, I was working on replacing the intake manifold gaskets on my car. Wouldn't you know it, a washer dropped into one of the cylinders and I couldn't get it out without taking off the head. Taking off the head wasn't too big of a deal, but putting it back on is proving to be a much more difficult task. When I first went to put it back on, most of the head bolts torqued down just fine, but a few stripped so I took the head back off to helicoil the ones that wouldn't torque. Turns out all of the holes had already been helicoiled so I decided to go out and get some timeserts for the stripped ones, put them in and threw the head on again. Wouldn't you know it, some of the helicoils that were fine last time stripped this time. I decided I'd just replace all of the old helicoils instead of wasting my time torquing and untorquing, removing and replacing the cylinder head. Unfortunately, I think I screwed the pooch. Most of them are almost perfectly drilled and inserted, but there is one that looks like the angle is just a little bit off. I'm still going to try to put the head back on and torque it with it like this, but if it doesn't line up well enough I'm trying to find a fix.

Now here's my question. Would it be possible to refresh the threads on my block? I'm not talking about just throwing a helicoil or timesert in it, but fill it with molten aluminum and drill brand new holes/threads into that. I know it sounds insane, but I'm thinking that, if it comes down to either buying a new block or trying this, this might work. However, I'm not an actual mechanic, I'm just a college kid that enjoys wrenching around every once in a while, so I could be talking out of my ass.

Any insight is appreciate, feel free to tear me a new one if this is one of the most idiotic ideas you've heard of.
Thanks!

(Too long, don't read; I possibly screwed up my cylinder head bolt threads in an aluminum block and wanna try pouring new metal into the threads to redrill and thread it if they are. Think it'll work?)


Tom Greenleaf
Ultimate Carjunky / Moderator
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Aug 22, 2015, 2:09 AM

Post #2 of 6 (1688 views)
Re: It sounds insane, maybe just crazy enough to work (Head bolt thread repair) Sign In

Greetings: Out of the gate you have a lot of hurdles with this. It's old now, Euro designs are both great and fussy in areas or hopeless, plenty of miles and I think this may be a car special ordered for export to the US (many were) so would have some differences that are fine just harder to find details.


This is full of snags that may be stoppers. It's been messed up before if you found Heli-Coils in the block already. Dissimilar metals namely alloys and steel types of many sorts do not get along well over time. Can you fix the block with adding more metal and gain enough metal to have strong, lasting threaded holes - yes but cost and effort would probably be too invasive vs another block - my guess. It's been butchered already doesn't help.


Appreciate your vigor for the project. It takes at least that much then the tools, equipment and experience which is IMO not something you grasp out of reading tons on the web as well as "seeing things done, doing the same such that when you can teach it you really have the knowledge fully acquired" - That was from a commencement speech at Harvard Medical school 1948 and still stands!


Good luck. What's you end goal for this car?


T


So - At the start you found a problem to fix and made a mistake dropping a washer. It found it's way out of your reach to retrieve it. Have to guess but with the right tools you could have retrieved it without taking off the head with high chances as if it got there it could come back out but lacked the tools to do that. The benefit though is you found a block already messed with now that you might not have known.


From this as a starting point now what is your situation for handling this? Can the car stay where it is out of the weather? Do you have both the budget for this and the help from a high end machine shop also capable of high end metal work/fabrication? You may have to send the whole engine block out and actually improve upon the OE flawed design. That or try another patch job this time with the help of local machine shop up to having someone look at the situation and be able to guess at the costs for you so you can make decisions from there.
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Just happened that an '87 300E (is stored on my premises) and retired from this or not end up with some near impossible dinky work on the thing enough so owner can use it now and then. Speedo well researched by owner is totally fixable for your car. I have the printout only paper so would have to type it all out by hand with my computer as I don't have the devices to copy it from now wrinkled paper in print. Problem if speedometer works but odometer and trip odometer do not is a nylon worm gear can just back out and do that or strip out and need new. The access to tighten one last brass ring is a page long alone! No special tools just time and pay attention not to break anything along the way. New dash bulbs suggested while there are the only new item required unless already broken or worn parts in that case.


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Like any battle what is your "exit" strategy? Keep this car or sell it off? Being an SL it would have more interest than most other models



RandomOriginalName
New User

Aug 22, 2015, 6:09 AM

Post #3 of 6 (1679 views)
Re: It sounds insane, maybe just crazy enough to work (Head bolt thread repair) Sign In

Thanks for the detailed reply! I've had some people tell me that my car looks like a gray market, but according to the vin and other information I've found it isn't. My end goal for this car is to just make it drivable. I originally bought the car when I was in high school because it had some problems and I wanted to learn how to work on cars. As for finding another way to get the washer out, trust me, I tried. I had the car sitting in the garage for about a month while I consulted my neighbor (a mechanic at a local dealership), other mechanics, and the internet. The washer was too big to take out of through the spark plug hole and the valve was only opened just barely wider than the washer so I couldn't fit anything down inside. I could've turned the engine by the crank to open the valve more, but I didn't want to risk scoring the cylinder in the washer was on the edge of the piston. Believe me when I say that taking the head off was the last thing I wanted to do.

The car is in a safe place out of the weather. It's been sitting there for going on a year now so my dad is starting to get a little upset with me, but aside from that it's fine. Budget is not something that I have right now (working with the income of a broke college kid) so a machine shop is a little out of my scope. I was thinking about doing this more as a DIY. It doesn't seem like it'd be too difficult to me. Except I'd probably need to have the block decked.

I know that the odometer is a common flaw with the 80s era Mercedes and I've already put new gears in there but it hasn't been on the road at all since I repaired that.

I have quite a bit of capital invested in this car, so my "exit strategy" is to bring it to a drivable state again, have some fun with it for a while, then sell it. The way it's sitting right now I doubt I'd be able to recoup much and I wouldn't feel right selling a car that doesn't run anyway. Also, when I had my neighbor over looking at the botched helicoils, he told me that my engine doesn't look like it's gotten anywhere near 195k miles put on it and that either someone must have replaced the instrument cluster with a high mileage one or the rolled the odometer forward. Either case sounds pretty stupid to me, why would you want to make it seem like you have a high mileage car?


Tom Greenleaf
Ultimate Carjunky / Moderator
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Aug 22, 2015, 6:44 AM

Post #4 of 6 (1674 views)
Re: It sounds insane, maybe just crazy enough to work (Head bolt thread repair) Sign In

I can't say for sure about the lost washer but if you knew and saw it in thru spark plug hole you could have cut it with a "nibbler" and taken it out! Water over the falls now.


OK - you still might need a machine shop. I don't know what it will take to make correct perfect holes for new threads for head bolts. I do have a clue the tools are unaffordable right down to the bits used. Think as doing it wrong could render it way too hard to make work?


Funny you chose or happened upon an MB for a car to learn on? As cars go you need more obstruction tools than most so not the easier of all to learn with + parts costly most of the time. Good news is most are always available!


Speedo? If you already did the nylon gears then check it by just spinning the speedo cable with a drill - that easy. Not running you should also be able to just hoist one (maybe both) rear wheels and spin by hand too and see it work.


Hey - if engine left apart for this long do cover things and I'd put some oil on pistons so rings don't lock up on you.


Good luck. If all fails and car out costs you, you might be surprised at what you could get for some parts and move on to something else,


Tom



RandomOriginalName
New User

Aug 22, 2015, 6:55 AM

Post #5 of 6 (1670 views)
Re: It sounds insane, maybe just crazy enough to work (Head bolt thread repair) Sign In

The speedo works fine, the gears that control the odometer were corroded and missing teeth. $20 for 3 new gears and 20 minutes later the odometer is fine. I spun the gears to make sure the odometer moved and it seemed to work fine, just haven't had a chance to test it for accuracy on the car. I have been applying oil to it every so often so as to avoid that and have been putting plastic bags over it to avoid things falling in.

I was more asking if this is actually a technique that people use to fix threads. I've been searching all over the internet and haven't been able to find any write ups or anything where people have done it.


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Aug 22, 2015, 7:15 AM

Post #6 of 6 (1668 views)
Re: It sounds insane, maybe just crazy enough to work (Head bolt thread repair) Sign In

Techniques for fixing threads? There are limits to the web. The real shop and person that would do this you probably need to go talk to with pics at first.


Mix of trades somewhat with that. Mechanically what would the engine require and welding then machine work possibly not a one stop fix with a chance prior attempt that failed is why you are in there to begin with? Can't know that from here.


Speedo. If it fit bet it's right ratio. If anything might read kilometers not miles or the other way? Laugh, if you want to know now measure the circumference of the tire's outside and spin one if not posi that is double speed and do the math for a mile 5,280 Ft. or a kilometer 62% of that!


Tom







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