When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Allow me to embarrass myself. Over 4 yrs ago, I did the bank 1 valve cover reseal on my 2010 C207 E350. It seemed like I was the only one on earth who had a previous owner ignore the pcv system to the point where blowby completely ate away at the sealant around the spark plug tube seals. Refreshing the famous pcv components meant little. Back then, there was NOTHING on the whole of the internet about this job other than 1 Pelican Parts article. I was much less experienced with wrenching than I am now, but either way I dug in.
The job went well and was 100% warranted when I saw there was in fact virtually no sealant left around the spark plug tubes. I cleaned mating surfaces to the point of obsession & used "The Right Stuff", following exactly what the can said along with the critically helpful Pelican article. My reason for this post is one small blunder made at the very end while in a sleep deprived stupor.
I listened to the torque wrench instead of my hand. A lifelong musician, most all I know is interpretation of life expressed with my hands. I knew the bolt was fully tight, but the lack of experience had me bowing to the almighty click of the torque wrench. A click that never came, & a bolt that snapped its head partially off. An almost nonexistent "seep" was observed for years & never addressed due to embarrassment and fear. I can't let this go any longer, it must be addressed. I change my oil every 5k mi & on average was going through 1L of oil during that 5k mi due to this bolt. A bit more now perhaps.
So, get the engine a little warm and possibly back the bolt out slowly just a bit, wait to cool and do the rest? Put a extracting socket on the bolt if the head comes fully off the get it the rest of the way out? Or be prepared with drill, various bits, etc? Possibly in need of thread repair? (Can't rule it out I suppose). Should I look into doing the valve cover reseal again, as the bolt only goes through the timing cover and valve cover itself? I look forward to replies from those smarter than I & who have hopefully been down this road before. Many thanks, and sorry for the novel. The culprit Head separated on the left side, still connected on the right Section of timing cover and valve cover which bolt threads into
If you're going to give this a go, then you need to be prepared to use an extractor of some nature. As its already compromised, the chance of removing it without it breaking are pretty low, but not 0% either.
I'd be hitting in with some good quality penetrating spray continually over a few days, something like Kroil to give it the best chance. Heat the area around the bolt (not the bolt itself) but not like it's cast iron - gentle heat only. If you can see the underside of the bolt, a few taps with a hole punch or similar to encourage it to move. Be careful heating anything alloy as its melting point is much lower than cast iron, as well as for any surrounding electricals.
Thank you very much. These were my thoughts as well. I was planning on getting some appropriate sized drill bits and the like. I have extractor sockets if the head snapped completely off and I was left with only threads, and new bolt is in hand so if needed I was also thinking of getting a helicoil in the appropriate size.
It happened while I was tightening and it's of course in a "clean" area free from any rust or corrosion so I'm hoping it being bound won't be an issue. The penetrating oil is still something I'll be including.
Given the valve cover itself is magnesium and the timing cover aluminum, do you think driving around to get it up to temperature would be enough heat? I do have a propane torch I could "kiss" it with.
I think you have one shot at it. Certainly the penetrating oil - and I'd overdo it with that - and then a warm engine won't hurt. Not sure there's anything else you can do until it either comes out or breaks. Best of luck
NO to the propane torch! If heat becomes necessary, use a heat gun with a small oriface that focuses the hot air.
Thank you! Once in there, I don't think I coukd've been foolish enough for the torch but is easy to type that up on a screen while simultaneously in a mild panic lol. The heat gun is certainly something else to add to the arsenal. I'm going to hope the heat from an operating temp engine block is enough given the small size of the bolt, it's low torque, and rust/corrosion not being in the picture.
There’s always the possibility that it comes out fairly easily, and the only reason it broke before torque is because there might’ve been sealant or something in the bottom of the bolt hole and it bottomed out before tightening. Ime
Ah, I hope so! Funny you should mention that. On the side that the head is separated, I can see little bits of sealant. I also stopped the second I felt/heard it crack. I'm definitely going to come prepared for the worst and hope for the best. I appreciate the responses. This has been eating at me for years. Like a teenager with pimples, every time I look at the car all I see is that staggered bolt head hahaha.
I will definitely update once accomplished in hopes it helps someone else.
The things we do for the cars we love. Ive broken plenty of NEW aluminum bolts using a proper torque wrench. Usually its valve cover bolts, or cam cover bolts. When reinstalling my magnets for the camshaft I think I broke three new bolts. Anything that stresses the bolts on install will break them. Ive learned to really inspect the threads well and even chase them with a tap for good measure. You can even hand thread the bolt before install to see that it will seat right when you are ready to mate surfaces. Off topic and not that its the same, but in some recent work on a friends old land cruiser that has some rust, I retapped every thread I came in contact with. In that scenario I broke lots of bolts that had been rusted for the past twenty years, which is why you'll see me recommend fluid film when people ask.
The things we do for the cars we love. Ive broken plenty of NEW aluminum bolts using a proper torque wrench. Usually its valve cover bolts, or cam cover bolts. When reinstalling my magnets for the camshaft I think I broke three new bolts. Anything that stresses the bolts on install will break them. Ive learned to really inspect the threads well and even chase them with a tap for good measure. You can even hand thread the bolt before install to see that it will seat right when you are ready to mate surfaces. Off topic and not that its the same, but in some recent work on a friends old land cruiser that has some rust, I retapped every thread I came in contact with. In that scenario I broke lots of bolts that had been rusted for the past twenty years, which is why you'll see me recommend fluid film when people ask.
That's good advice, especially as these cars get older. I almost always insert any bolt by hand as much as possible. To think you could be stopped for days just by cross threading a small screw on a cam sensor is just mad but the alloy these engines are made of is softer then we think it is.
You're both right and that certainly is good advice. I run everything in by hand and almost always run it down as far as I can by hand, but putting in the hardware before surfaces are mated is a nice extra bit of information. Whatever my eye misses will certainly be felt. The only time I've done that was to "store" hardware in place for a quick reinstall.
Getting in the habit of chasing threads regularly is also a good habit to form. Funny you mention those cam magnet bolts. Those things feel so fragile. I treated them like I was handling a 2 wk old kitten hahaha.....and I can sympathize with your friend's old Land Rover experience. I look after my mom's 3rd gen Acura TL (230k New Jersey miles, never garaged) and it's like working on a 40 yr old car sometimes. It is certainly no where near as "sealed up" as my C207 or sister's W203 I also look after. I basically replace every bit of hardware I touch on that thing.
I blew it with my can of Fluid Film, as in, it's already cold and wet. I always heard and read it's best when applied during the end of summer/early fall when still warm out for a proper bond?
I can't see anything wrong with the bolt head, is it on the lower part outside the photo ?
I would put some gentle heat from a gas torch on the piece where the actual thread sits, then try to loosten. Back and forth until it starts to turn more easily.
If it does snap, don't try drilling it freehand - it's only a small bolt (M6?) you won't be able to keep the drill straight & central. And with a small bolt like this, be very careful if trying any extractors, they easily break & then you'll have a worse problem. Use new sharp HSS drills if you must drill it; you'd need to make up a guide for the drill to ensure it goes down the centre of the bolt only.
Once removed, clean the thread of all residue with an M6 tap.
I can't see anything wrong with the bolt head, is it on the lower part outside the photo ?
I would put some gentle heat from a gas torch on the piece where the actual thread sits, then try to loosten. Back and forth until it starts to turn more easily.
If it does snap, don't try drilling it freehand - it's only a small bolt (M6?) you won't be able to keep the drill straight & central. And with a small bolt like this, be very careful if trying any extractors, they easily break & then you'll have a worse problem. Use new sharp HSS drills if you must drill it; you'd need to make up a guide for the drill to ensure it goes down the centre of the bolt only.
Once removed, clean the thread of all residue with an M6 tap.
Well, you were very correct on your analysis of the bolt head. Earlier this eve I found out the hard way why I thought the head was partially snapped off and why the bolt head was at a slight angle. Upon what seemed like an easy, slow, gentle extraction after getting the engine up to temp turned out to be a bolt broken halfway....deep inside the hole. All because I didn't listen to my hands and instead the torque wrench all those years ago. This is exactly why I left it alone for nearly 5 yrs! Time to gain some new experience....
Thankfully, the bolt is broken far enough in that I can (once again) remove the valve cover all together and deal with it that way which I'd much rather do for the sake of access and sight. I do have some fresh cobalt bits but perhaps will pick up some HSS bits tomorrow if I can find some locally. I appreciate your reply. I definitely won't drill it freehand either and may also try to get some reverse threaded drill bits while I'm at it. Good eye also as far as M6, and I do have thread chasers and taps for it. Total mess, but it'll be a great feeling to finally sort this out.
Well, the fat man and the elves are back at the north pole, New Years Eve drunks are once again well sober (maybe), and all of the oil is once again staying inside my M272 where it belongs.
Baltistyle, you were 100% correct. There was a little blob of sealant at the bottom of the bolt hole which the bolt of course hit before reaching torque. As mentioned in previous post, what I thought was a snapped head due to crooked angle, etc was actually a bolt snapped about 70% and I finished the break while try to gently turn it out.
A gift from God was the location of the bolt as well as being deep enough in the valve cover to remove the cover, have it in hand and easily extract the broken ******* via center punch, drilling a small hole with a carbon steel bit, then performing literal surgery with an HSS left hand threaded bit. I'm talking 1/84 (or something) of a turn at a time. Naturally, the bolt was broken jagged, so regardless of a decent center hole, that bit wanted to walk. I practiced with some rusted junk old hardware and scrap wood as this was my 1st time doing anything like this. Nothing like the pressure of knowing you can't screw it up.
Honestly, I'd rather drill out one bolt every week for the rest of my life rather than deal with cleaning sealant off of the cylinder head mating surface ever again. I will honestly sell this car before touching that again and buy an M113 car perhaps. The pictures look worse than they are and I had plastic bags EVERYWHERE to ensure nothing fell in there, but at the least there's far more shop towel lint than I care for. My fault for not getting something properly lint free. Lesson learned. I gently dabbed spots of lint with a fresh microfiber and lightly poured oil over the cams and cam adjusters before putting the cover back on. More hours of brake clean and plastic scrapers than I'll admit. Should've planned a month or so in advance and ordered some Loctite 7200 (I think it is?) & am curious how effective that stuff is.
Been about a wk now, and it's looking good. Thanks again to everyone who responded. I plan to make a separate thread on the valve cover because I still cannot believe how little mention there is on the entire internet about that job. Hopefully it means that few people have had to go through it.
Enough sealant?! Talk about lessons learned. Actually glad I re did it. Chased the threads and was good to go. Thankfully, there was nothing but bits of dirty sealant and not shredded metal. Huge stress. I never feel like a mating surface is good enough. Zoomed in, the surface looks like Hell, but doesn't appear so in person and all was perfectly smooth to the touch w/ fingertip and somewhat long nails I use on my right hand for guitar.
Thanks guys, I appreciate it! Bloxham, it was a steel bolt actually. The fact that it was in the valve cover itself & I could still remove it and have it in hand for drilling was seriously a gift. I couldn't imagine if it was one of the lower bolts in the cylinder head.
I definitely did laugh too when I saw that tiny thing finally come out! To think of the trouble that 1 half broken M6 bolt can cause! I haven't fully confirmed this, but I heard of at least two people mention the M272/273 valve covers themselves are paired perfectly to each cylinder head? As in, if you need to replace it for whatever reason you'd need to also replace the entire head to have proper fitment?! Again, no clue to the truth of this. I didn't see the covers available anywhere new, but used ones are floating around. Given the integration of cam journals in the cover and the specific loosening order to ensure it doesn't warp, I'd never trust those used ones. Very greatful it didn't come to that whatsoever!
To think of the trouble that 1 half broken M6 bolt can cause! I haven't fully confirmed this, but I heard of at least two people mention the M272/273 valve covers themselves are paired perfectly to each cylinder head? As in, if you need to replace it for whatever reason you'd need to also replace the entire head to have proper fitment?!
Yes, this is true. Doesn't mean you can't get away with 2nd hand valve covers but MB does specify if the covers need replacement, then the heads do too. Crazy stuff.
Last edited by BlackML550; Jan 13, 2025 at 05:22 AM.
Good God man, that is crazy. Sometimes things like this make me think that having a later M156 with a plastic valve cover isn't such a bad thing after all hahaha....
I will say this. Yes, I have saved big on brakes, suspension, and rear tires, but besides those items I'm not sure I did myself many favors passing up on 211 E55's that were very near the same price as this 207 E350 was in early 2020. It hasn't been bad at all really, but seems like it's basically the same diagnosis and work at the end of the day. Or 207 E550's for that matter.
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
