A 4" porthole has to be put in behind the rear crossbar.
I went through the suggestions that have been posted & it boiled down to wasted time. Plus once you get the bolts out the plate in the hull will fall out & you will have to put in a porthole anyway. it is a good thing to have the porthole for a spooge to soak up water in the future. Doug

Does the plate have to fall out if you put a bolt back into one or two of the other holes before drilling out the stuck ones? When I replaced the bow handle on a Sunfish (I know, a monodull, but still...) I made sure that I kept one bolt in at all times to keep the plate from falling down.

you can do that but you still end up with the corrosion problem down the road so the port is needed and quite handy to have for storage .

Drill it out and put a thread insert in. The hole location will be in the same place, you can still use a 1/4-20 bolt.

Use loctite on the insert so it's thouroughly attached to the backing plate and put anti sieze compound on the 1/4-20 bolt before you bolt it all back together.

You'll have to slap a little resin on the transom where you drilled oversize for the insert but it'll pretty much all be covered up by the gudgeon anyway

I thought about inserts - I'll have to see what material is available. In addition, it may be possible to simply drill two new holes in the existing gudgeon and drill and tap new holes into the backing plate, leaving the gudgeon in the same position. Not as desireable as using the same holes, but worth a thought. The machinist here at work suggested using a pre-drilled block to guide left-handed drill bits (going from smaller to larger sizes) to drill out the bolts. He said that occasionally the left handed drills will catch in the bolt, and will be turning in the right direction to back the bolt out. The vibration from drilling into the bolt might loosen some of the corrosion, and make taking out the bolt possible, he says. He also added that he only felt that I "might" be able to drill out the bolts. I ordered some left handed bits today - should be here tomorrow. We'll see..............

Peter your spending a few dollars on tools if that doesn't work take it to your local vehicle workshop and they will tap it out for you. It wont cost much they do it all the time on old motors. For attatching stainless fittings to aluminium get a tube of the anticorrosive gunk to put on all your bolts, rivets etc
regards

If it were me, I'd drill the bolt out (carefully) and re-tap with a slightly larger bolt. You'll probably have to enlarge the holes in the gudgeons (or tap them out too).

If that didnt work, I'd put in two port access covers and go back to the original size bolts and add fender washers and nuts on the inside. A little silicone in the holes before assembly will keep it waterproof.

Drilling holes in a new location sounds like a bad idea, lots of opportunity to for mis-alignment.

Bill

Looks like I've got my work cut out for me this coming weekend. I'll pick up some Blaster and my left handed bits and give drilling out the bolts a go. Hopefully using care and some appropriate guide blocks will do the trick, and I'll be able to clean up the threads in the backup plate with a tap and be done. If not, I came across a "broken screw extractor" today which could be used as a last resort. It's essentially a 3/8" diameter hardened steel tube with saw teeth milled into both ends, and it has a bore of slightly more than 1/4". I tested it, and it does cut aluminum, although because it has no set to the teeth, it has little clearance for the chips and has to be extracted every 5 seconds or so and cleared. Using a guide block with a 3/8" hole, I could cut down around the outside of the bolts, through the glass and the aluminum backing plate, and remove the bolt like a wooden plug in a hole saw. McMaster Carr catalogue has a stainless threaded insert for a 1/4-20 bolt which has an external 7/16" thread, which could be tapped into the hole in the backing plate and epoxied in place. Then I'd theoretically be back in business, once I fill the enlarged hole in the glass back up. But I'd rather go the other route, if possible. I'll let you all know how it turns out. Thanks for all the great brainstorming. This forum is great!

Peter

Got 'em out! PB Blaster and the bolt extractor worked on one of them, once I had a proper hole bored in the end of the stud using a cobalt drill bit. The bit that came with the extractor was useless. The other bolt was a lot more work. Using the broken screw extractor (see earlier post) and a wooden guide block with a 3/8" hole in it, I bored a 3/8" hole around the outside of the broken bolt. Since the extractor's ID is only slightly more than 1/4", it used the bolt itself as a guide once it got started. I drilled as deep as the aluminum plate. I then cut a length of 3/8" thin-wall steel tube, and inserted it into the hole in the transom, so that it protruded about 1/4". This gave me a reference fitting for my drill blocks. I set up a fence and stop on my drill press, drilled a 3/8" hole 1/4" deep into the block, and, using the same setup, drilled the guide hole for my bits to drill into the stud, exactly centered on the 3/8" hole. I used my Dremel with a silicon carbide grinding wheel to give me a flat on top of the stud, and used a spotting drill bit in one of my guide blocks to get a start. I then started with a 1/8" bit and worked my way up to a #7, and then cleaned out the threads with a 1/4-20 tapered tap. Trick is to drill SLOW, maybe only 100-200 rpm, with lots of pressure, and cutting fluid. If you build up heat, you'll work harden the stainless. Careful not to let the bit grab and snap off (don't ask). The relief I feel right now is priceless. Now to finally finish off this boat and get it into the water. Thanks to everyone for your ideas and support. Hopefully my experience will prove useful for someone else.

Peter Shapiro
P19MX

Fantastic! Congratulations, and once again we see the truth that persistence, time, and hard work sometimes actually pays off. <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />