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Re: Broken Head Bolt Repair

Originally Posted by hawkfan9

If you find yourself doing this kind of work frequently enough, keep your eyes peeled for a horizontal milling attachment for the Bridgeport. I have one for mine, and while I don't use it often, as I have a Kearney and Trecker 2K universal horizontal mill for big work, it's still a nice tool to have access to when you need it. Nice work! Fixturing and holding work is always the main battle.

Thanks, I'll keep that in mind.

-Don

Re: Broken Head Bolt Repair

If you find yourself doing this kind of work frequently enough, keep your eyes peeled for a horizontal milling attachment for the Bridgeport. I have one for mine, and while I don't use it often, as I have a Kearney and Trecker 2K universal horizontal mill for big work, it's still a nice tool to have access to when you need it. Nice work! Fixturing and holding work is always the main battle.

Re: Broken Head Bolt Repair

plastic gear is in use here and there but never saw plastic cams!
as mentioned, the big end and crank need to be checked for roundness. probably all out of whack me thinks.

Re: Broken Head Bolt Repair

Originally Posted by farmshop

Kawasaki engine? Some of the Deere’s that ran Kawasaki’s had plastic gears known to fail

I asked John and he said that it was a Briggs and and Stratton engine.

-Don

Re: Broken Head Bolt Repair

That was quite the process; thanks for bringing us along with you.

I'd be concerned regarding the concentricity of the rod end; what with the loose bolts allowing it to pound back and forth on the crankshaft.

Re: Broken Head Bolt Repair

Kawasaki engine? Some of the Deere’s that ran Kawasaki’s had plastic gears known to fail

Re: Broken Head Bolt Repair

Plastic cams...I have never seen that before...Chinesium?

Re: Broken Head Bolt Repair

My buddy was a mechanic at a motorcycle shop, but he grew-up in his dads welding welding business and was an accomplished weldor. He would remove broken bolts of all sorts in an aluminum engine by blasting them out with an O/A torch. For whatever reason, he never disturbed the aluminum threads.... (you had to clean them out, but they were There)

Re: Broken Head Bolt Repair

Originally Posted by crab fisherman

Rod bearing condition? Crankshaft damage? The oil looks pretty muddy.

The cam shaft has plastic overmolded cams. The loose connecting rod bolts hit the plastic cams on the cam shaft and gouged it as shown below.

15. Gouged cam shaft
Attachment 1715372

Re: Broken Head Bolt Repair

Originally Posted by crab fisherman

Left hand drill bits are remarkably reliable when drilling out broken bolts or studs (if they are threaded).

I have purchased single left had drill bits for specific projects, but I never invested in a set. I didn't think that they would be effective in this case because the head bolt was over tightened and smashed into the imperfect threads at the bottom of the hole.

Originally Posted by crab fisherman

A big question is WHY did the rod cap bolts become loose? Rod bearing condition? Crankshaft damage?
The oil looks pretty muddy.

Yes, why did the rod cap bolts become loose? My friend John's theory is that the dirty oil caused excessive heat that could have caused the cap bolts to loosen up. Perhaps someone else on the forum has other better theories.

Originally Posted by MinnesotaDave

Really nicely done - I like the cleats too

If you make yourself a big 90 degree fixture, I think maybe your cleats could have been used there and saved you the trouble of turning the head?

Using a angle plate was my first thought, but as you can see the motor and cleats would require a large angle plate. I have some angle plates but they were way too small and I didn't have enough large scrap metal to cobble up one. It isn't a huge job to rotate the head and align it. I have the head alignment tool shown below that makes it pretty easy.

14. Bridgeport head alignment tool
Attachment 1715371

Originally Posted by John T

Nice job.
Its amazing how sometimes a 10 minute job turns into 3 hours....

Yes, exactly

-Don

Re: Broken Head Bolt Repair

Nice job.

Its amazing how sometimes a 10 minute job turns into 3 hours....

Re: Broken Head Bolt Repair

Really nicely done - I like the cleats too

If you make yourself a big 90 degree fixture, I think maybe your cleats could have been used there and saved you the trouble of turning the head?

Re: Broken Head Bolt Repair

Very nice job documenting your project!

Left hand drill bits are remarkably reliable when drilling out broken bolts or studs (if they are threaded).

A big question is WHY did the rod cap bolts become loose? Rod bearing condition? Crankshaft damage?

The oil looks pretty muddy.

Thanks for sharing and pictures!

Re: Broken Head Bolt Repair

Good job on the repair but for most it would cost more than a new engine.

Re: Broken Head Bolt Repair

Nice job. I've used that TIG trick a time or 2. The customer is always amazed

Re: Broken Head Bolt Repair

11. Drilling out head bolt
Attachment 1715333

Next I wound out the portion of the screw that was still in the female threads. (The portion that I removed looked like a Helicoil). To clean up the threads, I ran a tap through the hole..

12. Cleaning up threads with tap
Attachment 1715334

The Bridgeport allowed me to have the rigid setup and center the drill bit on the broken head bolt. As a result I was able to drill that bolt without damaging the original threads in the Aluminum head, for the first time. If the drilled hole wanders, which it often does, I have to drill oversize and use a Helicoil.

13. Tapped hole cleaned up
Attachment 1715335

-Don

Re: Broken Head Bolt Repair

Unfortunately my welded nut wasn't strong enough to extract the broken off portion of the head bolt. My welded nut broke off which meant that I would have to drill out the broken off head bolt. To support the motor I made some cleats to help me to clamp the motor to my Bridgeport.

6. Counter boring cleat
Attachment 1715328

7. Cleats done
Attachment 1715329

8. Cleats mounted to motor
Attachment 1715330

9. Motor clamped to Bridgeport
Attachment 1715331



The flat surface on the motor was 90 degrees to the head so I had to rotate the head of the Bridgeport to drill out the broken off head bolt. I used a 1/4” drill to remove the center portion of the broken off 5/16”-18 UNC head bolt, without damaging the tapped hole in the head.

10. Head of Bridgeport rotated
Attachment 1715332

Broken Head Bolt Repair

My friend John's buddy brought his lawn mower to a lawn and garden repair center because it was making a clattering noise. The center told my friends buddy that there was a broken connecting rod and the mower wasn't worth fixing. When John took apart the engine he found that the original problem was that the connecting rod bolts were loose, which would have been an easy problem to fix.

1. Loose Connecting Rod
Attachment 1715323

During the reassembly of the head, the center broke off one of the head bolts. In fairness to the center the bosses on the head are different heights and some of the holes are through and some were blind. To make up for the different heights, spacers were added to the shorter bosses on the blind tapped holes, to keep the head bolts from bottoming out on the imperfect threads on the bottom of the hole. I believe that the center didn't put a spacer under the head of the head bolt on a short boss with a blind hole and kept tightening the head bolt after it bottomed out and broke it. The broken stud is located on the upper right hand side in the following picture.

2. Broken off head bolt
Attachment 1715324

Here is a close up of the broken head bolt. you can see that the break is about 1/8" below the surface and you can also see that all of the holes are counterbored.

3. Broken off head bolt close-up
Attachment 1715325

My go to method for broken off bolts is to TIG weld an extension to the broken bolt as shown below and then to weld a nut on the top of it. This method works very well for rusted bolts because the heat from welding expands the bolts and crushes the rust on the threads, to create some clearance.

4. Head bolt built up
Attachment 1715326

5. Nut welded to head bolt
Attachment 1715327