Zman's Outboard Motor Guides - Repairing thread hole

Bolt Hole Rethreading / Tapping

BROKEN BOLTHEADS

If you happen to break that bolt on the powerhead, you are in for some work. For this particular repair, my suggestion is for you to take to a machine shop or a reputable repair shop and have them drill the bolt out and rethread the hole or ................. if you insist, you can do the rethread. The pros have all the equipment for this particular job.

It is very hard for you to do this particular job, not impossible but will be beneficial if have a drill press. Make sure the drill press has enough room / depth for you to position the block so you can access the bolt hole. You may have to remove the carburetors and other components just to access the bolt in a press. The motor will more than likely have to be removed from the boat and will have to be laid with the bolt hole facing up.

Using a hand drill is not advisable for powerhead bolts, these drills tend to walk and you may end up destroying the powerhead beyond repair, thus that is why it should be left to the experts. If you insist on repairing it yourself, I must stress the need for a drill press. This will guarantee that the drill does not walk and it will hold the needed angle. If you drill the wrong angle, you may not get the seal you need and you may end up drilling through the bolt hole into the body of the powerhead. If you take the job and decide to do it yourself and find the repair to be messy or it did not go as intended, there are options for repairing that bolt hole for a second try. (Read On)

Start with a bit that has a smaller Outside Diameter than the bolt that is frozen. You want to initally try to preserve as much of the original metal on the powerhead as possible. When you have a hole that is the same depth as other holes, start grinding with a roto zip or dremmel at the remaining portions of the bolt, being careful not to grind threads. When you get to the threads, you will need to snake / push old bolt that is stuck on threads with a bent nail. It takes a while but is the best way and you get to keep original threads.

If you are not interested in all that work, obtain a Helicoil set for the bolt that you are trying to rethread and go from there.

Repairing bolt hole on powerhead with tap / brazing metals

First and foremost, if it is the powerhead bolt hole that needs repair, you must put motor on stable flat surface. This may require that you disassemble motor down to the powerhead. This of course will speed up your learning curve as it does require getting to know your motor. This will also give you a chance to replace all gaskets.

The picture on the left or above represents a mistake that I made. I tried drilling a broken headbolt out while the exhaust cover was still attached. I was hoping the cover holes would help guide me in, but the shaving blocked my view. This was my 6th bolt for the day and I was getting lazy and the result of my impatiences and its reward - more work and an almost worthless powerhead. I will go over repairing this mistake.

You will need a few tools. Here is a list:

Propane torch
Tap and Die set with the sizes you need
Drill bits for cutting steel / metal alloys
Compressor with nozzle attachment or compressed air in aerosol can
cutting oil for steel
drill press or hand drill if you are patient and careful
Possible carbide tip cutting bits (dremmle and rotozip)
magnetized screwdrivers (for collecting metal shavings)
Painters masking tape (covering up areas such as cylinder bores)
Safety glasses

It is best that you remove the powerhead, not absolutely necessary as I have done a few taps with the powerhead still on boat. It is imperative that you have adequate lighting around the area you are working on and have a workbench with all tools necessary. It is frustrating to have to look for items and you don't need any additional stress while doing this particular job.

If you are atttempting to braze, you can go to your local Lowe's, HomeDepot, Norther Tool, Harbor Freight store and obtain a propane torch or butane torch. Look in the welding area as it will have a wider selection of tools (try to avoid plumbing as they have basic torches). You will need to get a torch with a hose attachment as you will be moving the torch while it is facing down or at various angles. I believe the propane torch reaches a higher temperature while butane may be slightly lower. The propane torch will blow wider longer flame. You should be able to find butane torches that are suitable as they can reach temperatures high enough to melt the metal rods you use, but usually only cover a small area. After using both, I like the propane as it has a wider torch and gets so much hotter; make sure you wear gloves.

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