6HP Johnson won't idle, runs rough and misfires - help!

[AlTn]

Re: 6HP Johnson won't idle, runs rough and misfires - help!

wellllll...that "scoring" is sorta subjective...if it's to the liner it's gotta be smooth to the bore and hopefully not so deep that the compression ring on the head gasket can't seal it...if the score extends to the deck of the block, some jb weld cured then sanded as uniformly to the deck surface as possible may provide a surface that the head gasket can seal from a water leak...again, a machine shop can provide specific advice upon inspection...unless you can provide a pic of the damage, then many here can provide further advice

 

[jay_merrill]

Re: 6HP Johnson won't idle, runs rough and misfires - help!

My plan now is to forget trying to remove the sheared bolt and drill and tap a new hole between the sheared bolt hole and the adjacent cooling duct. There's less material to work with so I'll go for a size down. I reckon it'll work just fine.

This sounds like a really, really, really bad idea! If the rest of the motor is in decent shape, take the powerhead to a machine shop and let them get the stud out.



???

 

[Swell]

Re: 6HP Johnson won't idle, runs rough and misfires - help!

I've attached a pic. I got the bolt out, and the sheared screw extractor, as you can see - bit of a hatchet job but I'll drill it out to a bigger diameter, tap it and fit a bigger bolt, which should hold just fine. There's enough material to do that.

Most of the damage to the block is to the outside edge so it should fill ok and I'm not too worried. The pic shows the scoring to the end of the cylinder bore - the inside surface of the bore is fine. This is my only worry. It really is a shallow scoring, but it will leak unless the head gasket can expand into it. I reckon I either fill it or grind the whole surface.

Is JB Weld the same as Chemical Metal? I have some of that and I suspect it's similar stuff. Already used some on the water pipe mount inside the leg.

 

[jay_merrill]

Re: 6HP Johnson won't idle, runs rough and misfires - help!

Put a helicoil in it, so you don't have to drill out the head too.



???

 

[jay_merrill]

Re: 6HP Johnson won't idle, runs rough and misfires - help!

Is JB Weld the same as Chemical Metal? I have some of that and I suspect it's similar stuff. Already used some on the water pipe mount inside the leg.

Why did you have to use Chemical Metal on the insertion point for the water tube?



PS: I have to catch a couple of hour break in rainy weather to go empty my crab traps. In the mean time, just a suggestion - you seem to be trying to fix things in ways that are more likely to cause problems than they are to be successful. For this reason, I strongly recommned getting advice here and thinking about it, before you act. You will probably save yourself a bunch of headaches.



???

 

[Swell]

Re: 6HP Johnson won't idle, runs rough and misfires - help!

Why did you have to use Chemical Metal on the insertion point for the water tube?



???

There was a chunk missing from the inside edge of the grommet mount, opposite the small hole to the outside where the lug on the grommet locates. There was never a good seal. At least that's how it looked - I assume it's not meant to be like that!

 

[AlTn]

Re: 6HP Johnson won't idle, runs rough and misfires - help!

the "score" looks pretty superficial, however, I agree with Jay, a helicore or thread insert of some kind, is your only option for that head bolt hole...it won't be an easy "drill" for trueness if you don't have a press and some way to hold the powerhead precisely, besides that, it seems some weld build up may be in order first...just sayin'...machine shops do this kinda stuff all day every day...at least the shops geared towards automotive and marine repair

 

[Swell]

Re: 6HP Johnson won't idle, runs rough and misfires - help!

I have to admit, I screwed up that bolt removal. I'm reasonably technically minded and have an arsenal of tools, but for some reason when I drilled the bolt I drifted off centre and rather than stop and grind it back to flat and start again I kept going - which is why it all went so wrong. However, hopefully I can at least retrieve the situation.

Is a helicoil definitely the best option? Threaded aluminium is fine provided the thread is not used regularly, which in the case of a cylinder head it won't be. However, I suspect in this case it is the best option as it makes makes the best use of the material available and reinforces it with steel.

If I use helicoils, what would be the best size? The head bolts are obviously imperial, and measure up at about 5.7mm. The bolt actually mounts reasonably tightly in the hole as it is - not suggesting that's ok to use, but that also suggests that an M6 helicoil would work ok - that uses a 6.3mm drill which should help clean up most of the damaged areas.

Any tips on this would be greatly appreciated!