Broke an Exhaust Manifold Cover Bolt ...... HELP

[MokiCruiser]

I was farting around all day with this mighty 1975 Johnson 70 hp motor I recently acquired, trying to figure out why it wont start. Actually turning the key does nothing at all so when I say won't start I mean turning the key does nothing at all. So I found on the internet a step by step test procedure to isolate where the trouble is, and it turns out that it is connection between the solenoid and the neutral on the ignition or the safety switch itself ....................... unfortunately in the process of narrowing down where the problem was, the first step was to remove the small black lead from the solenoid that's grounded to the first bolt on the exhaust manifold, and as I was so foolishly (too hard) trying to back it out, it snapped off leaving about 2 threads. Now this bolt is about 1 1/2 inches of smooth before the threads, and as I said it snapped with just a bit of the threads. So my question is this. First I don't know how long this bolt was to start with so I'm not sure how deep to drill, but if somebody knows the length, can I drill and tap in a new bolt without doing any damage ........ damage as in shavings falling someplace that they shouldn't be. Thanks ahead

 

[Vic.S]

You might be able to look up the shank lengths for standard bolts and deduce the total length but there is no guarantee that it is a standard bolt.

You could remove one of the others and measure it.

 

[oldboat1]

Think there is a double ended screw up there on the exhaust manifold cover, and looks to be a likely ground point(?) -- maybe that is what broke off. In any case, you might lube up the bolts (soak them overnight) and remove the exhaust cover. With the cover off you might be able to remove the broken one with some care and a pair of vise grips. For a salt water motor in particular, it would be a good idea anyway to clean out any corrosion under there.

 

[MokiCruiser]

Yeah, I now I can remove the cover ............... I just don't want to mess with those other 18 bolts. It might open a bigger can of worms than I'm willing or able to tackle. I really have no clue but I'm guessing that this exhaust manifold cover was last off when this engine was built in 1975, and all I want to do is get this engine running and tuned up, not rebuilt. At this point, drilling and re-tapping in new threads sounds way easier. I suppose if I don't drill too far into the head, say 1/2 to 5/8 I'd probably be OK. Looking at the pictures in the manual it doesn't look like and shavings from tapping will go anywhere but out the hole.

 

[oldboat1]

might be fine as is, relocating the ground. If anxious to go fishing, think I would try it.

 

[StarTed]

I just removed a couple of broken bolts from my 1976 75hp evinrude. It was a bear but this is what I did.

Since I can't seem to keep in the exact center of a steel bolt in an aluminum thread I opted to try soaking them and using heat sparingly from a small propane torch. It took almost a couple of weeks but they finally gave up and came out.

They took drilling all the way through. I could tell when the drill went through because it dropped when exiting. The hole is almost always deeper than the bolt goes in.

Then I used a screw extractor carefully not to break it. They are very hard and brittle so any sideways thrust can easily snap them. Don't even think of breaking a screw extractor off. I soaked them with penetrating oil and alternated heated and cooled the aluminum with a small propane torch. It probably didn't get much hotter than a well warmed up engine.

Finally I tried using a mix of acetone and Marvel Mystery oil instead of ATF. More heating and cooling then finally they gave up and backed out nice and clean. It was a struggle and took lots of patience. Meanwhile I worked on my boat.

Hope this helps.

 

[MokiCruiser]

Thanks for the tips. After I wrote this yesterday I spoke to a mechanic that specializes in older Johnson's, and he said the same thing about just leaving it alone rather than trying to drill and tap out some new threads if it's not leaking exhaust with it missing. After all, It is only one bolt out of 18 on the exhaust cover. I think that I might just get a short 1" long 1/4" bolt, stick some wire between the bolt threads and the smooth bore in first inch and a half of the hole to give it some grip to thread itself in so I can re-attach the ground wire right where it was.

 

[sedaohr2]

Thanks for the tips. After I wrote this yesterday I spoke to a mechanic that specializes in older Johnson's, and he said the same thing about just leaving it alone rather than trying to drill and tap out some new threads if it's not leaking exhaust with it missing. After all, It is only one bolt out of 18 on the exhaust cover. I think that I might just get a short 1" long 1/4" bolt, stick some wire between the bolt threads and the smooth bore in first inch and a half of the hole to give it some grip to thread itself in so I can re-attach the ground wire right where it was.

Your situation is exactly what I have on my hands. I also looked up the pictures and have decided not to try to fix this since the manifold will like stay sealed without it. Messing around to take the others out and then still need to remove this and maybe others has high risk of more problems. I had a broken anode bolt on my lower unit and it resulted in som modification after many hours trying to drill and tap out.

 

[saltchuckmatt]

Do not repost old threads....a big "NoNo"

Start your own and explain that you've been reading.....