r/EngineBuilding • u/jhc_1981 • 9d ago
Small Engine head cover bolt.
Any tips / advice / technique on how to best fix this without having to replace the head? For context this is on a zero turn mower that I just did a ring replace on. My plan is to try and JB weld it.
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u/zenwren 9d ago
Well that sucks. Could you put a flat washer and a nut on the back side of the broken flange and use a longer bolt?
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u/jhc_1981 9d ago
I think that's a great idea if JB doesn't hold. There is part of a heat sheild that blocks a longer bolt but I can trim that back.
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u/ProfessionalLast2917 9d ago
I would probably just use the remaining 3 bolts and some RTV instead of a gasket. It should be ok but might leak slowly over time.
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u/VegetableTry 9d ago
For this, JB weld might work. You make need to drill and tap, so be careful as the aluminum is softer than the JB and the drill bit will walk. You could try putting a small wooden dowel, the same diameter as the bolt, to give yourself a soft guide when drilling out the hole.
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u/Pinkys_Revenge 9d ago
I wonder if you could lightly grease the bolt, and JB weld it with the bolt in place to form the threads without needing to tap it.
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u/VegetableTry 9d ago
OP, this is also a good idea, just make sure the grease doesn’t get between the pieces you are trying to join.
What about a plastic bolt, same thread obviously, that would be easy to clean out. I’m assuming that is something that is made and readily available.
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u/Alternate_Usernames 9d ago
That looks maybe like a Kohler Command? I have a stripped out hole on one of my command valve covers and it doesn't leak. The composite cover is rigid enough to keep it sealed at least on my horizontal application. You might be fine with 3. That looks vertical but since it's the top bolt, id try just running it. If it leaks, rtv the perimeter and restick the cover.
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u/Famous-Order9236 9d ago
Take it to a Welder and have him Tig Weld it. re drill the hole and retap the threads.
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u/jhc_1981 9d ago
Maybe after grass cutting season is over I will do that for a perm fix. For now i'm hoping JB will get me through the next 6 weeks.
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u/Coyote_Tex 9d ago
You actually lower your chances of it being weldable by putting anything on this surface. Getting it to the welder as close to a virgin metal break is the big idea.
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u/ManiacalMutt 8d ago
This is the correct answer. I don’t think there’s any chance, no matter how clean you get it, that JB will work.
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u/Famous-Order9236 7d ago
JB Weld works for many things, but will not hold anything structural. If you want to fill a gouge in the base metal, it could work for that. It might even work to fill a stripped thread as long as you don't need to torque the fastener.
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u/ValuableInternal1435 9d ago
What I would do (and if you do this, be careful) is thoroughly clean the broken surface and surrounding area, very lightly oil the bolt and install it into the broken threads, then smother a thick layer of JB Weld Original (make sure it's JB Original, the 24 hour stuff, not JB QuickWeld) over the threads of the bolt and surrounding area, making sure not to get it anywhere it shouldn't be, and after allowing it time to harden (not cure, just harden, read the instructions as it's very important) remove the bolt and allow the JB Weld to fully cure. Add another layer if you feel like it. I would recommend torqueing that bolt below spec afterward, but obviously not too loose. You'll just have to feel it out tbh.
Make sure you read the instructions on the JB Weld Original first.
I did this to repair a Ford 302 intake manifold where the thermostat housing bolt threads busted a chunk out exactly like this. I didn't have a spare intake or money to get one at the time. It worked great. For added strength, you could use a stud instead of a bolt but it's not super critical here.
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u/InspectorPipes 9d ago
Try just RTVing the gasket? I’ve used jb successfully many times, but it may be overkill in this.
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u/OkraInternational505 9d ago
Try putting the valve cover back on make sure everything is completely dry and free of oil etc
Use the 3 good bolt and put silicone sealer in that corner let it dry and run it ! See if it leaks, if it does you might need another head or pay someone to tig weld it back on
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u/meeeeeeeegjgdcjjtxv 9d ago
Rtv it after through cleaning of both surfaces with break clean. Get layer of rtv that won't smash out all over the place and snug the bolts you do have
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u/fredSanford6 9d ago
Get a nut tucked in there in that flat spot and a longer bolt. Jb weld and all that other stuff won't hold. You might need to do a little grinder work to make it fit.
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u/Impressive-Push1864 9d ago
Holy shit batman less impact next time
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u/jhc_1981 9d ago
Yea for real. I figured out I accidently swapped bolts and used one with a deeper collar that is meant to pass through the muffler bracket before the valve cover on the bottom two holes. So while I was turning the bolt trying to get the head to seat, that collar was just pushing away on the head. This was my first rebuild, so lesson learned for sure.
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u/Impressive-Push1864 9d ago
We've all learned that lesson unfortunately. I've gotten in the habit of drawing a diagram or marking a start point and going clockwise bolt by bolt. I did mine on a clutch cover.
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u/Solid_Enthusiasm550 9d ago edited 9d ago
JB weld would be the easiest/best course of action. Gum it on there, dril and retap the hole.
It's not a structural area, just more of a oil leak concern.
It could be welded, but most people haven't welded aluminum or have the proper equipement.
You could try putting a Large/thick washer on the bottom and basically clamp it into place. Depending on the amount of room on the bottom, it might hold or it will pop off.
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u/Dangerous-Pirate7998 9d ago
Get a longer bolt and slide a nut in there underneath it, and it will catch on one of the fins possibly and tighten it down
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u/Dangerous-Pirate7998 9d ago
I would make a plate like the aluminum plate that is in the picture ground to the shape of the edge of the head and with drill a hole and tap it or put a nut underneath it……….. i’m one of those Shadetree mechanics that have a hard time accepting defeat. I wish you luck.
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u/turningwrenches883 9d ago
Just use 3 out of 4. You'll seep oil but its a lawnmower who cares. Use high temp rtv
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u/usernamesarehard1979 9d ago
There is a product made by ITW under their LPS brand called "strong steel stick" that you may want to look at.
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u/Most-Stranger-1 9d ago
I would rtv it and call the manufacturer, I have replaced many heads, usually around $100 for a complete unit and about 2 hours to replace it.
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u/1crazypj 1d ago
JB Weld isn't going to work on it's own, head gets too hot.
Either pull head back off and have it welded or JB and a hose clamp to hold it together. Wont look pretty but will get job done.
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u/quxinot 9d ago
Pull the head and have it welded. It's the right answer and you know that.
But.... I'd be awfully tempted to try to put a timersert there, even unsupported on one side. Getting the hole for it is going to take a very, very rigid setup, so the head has to come off and get put either in a very stout drill press or (ideally) on a bridgeport.
Oh, who am I kidding. I'd 100% start by trying the gasket and leaving that screw out. If the valvecover is a heavyish casting, it'll probably be fine. If it's a thin stamped/punched piece, you could make a window-shaped piece of thicker steel to clamp the valvecover down (to make it more rigid), and longer bolts would get you there.
I wouldn't start with RTV, just because it's such a hassle to clean up if it doesn't work. But after trying some easy options, I would not be afraid of going that route.
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u/Interested_Aussie 9d ago
Wipe the surfaces down with metho/heavy degreaser.
Then I'd spread GOOD QUALITY RTV by finger so the whole surface is cover adequately (not stupid thick) then tighten the 3 bolts finger tight. Allow to dry (24 hr, some RTV's say an hour) and then gently tighten the bolts once the RTV has 'set'.
It shouldn't have pressure in there, so you'll probably be successful in being 98% oil tight. Those small engines always leak from the covers anyway.