Semi race motor advice

[whitehause]

Working on the crank right now. Got the plugs out and cleaned. Now in GC's book he suggests tapping the plug holes. Is there a problem with replacing the plugs with new ones or is the thought that high RPM might cause them to come loose? I have taps, but it's a forged crank and I'd hate to break one off in there and cause bigger problems.

[fp55scca]

Working on the crank right now. Got the plugs out and cleaned. Now in GC's book he suggests tapping the plug holes. Is there a problem with replacing the plugs with new ones or is the thought that high RPM might cause them to come loose? I have taps, but it's a forged crank and I'd hate to break one off in there and cause bigger problems.

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--Tim, absolutely tap due to high rpm. Loss of a welsh plug would toast a motor immediately. Pay close attention to GC's guidance on tapping, and use liberal amount of lubrication when you do it (don't ask me how I know this). Follow all GC's guidance on cleaning and crank prep.

[fp55scca]

--Tim, also pay attention (page 93) to countersink big-end oil journals, and teardrop mains.

[friedman]

I'm waiting for Jim's motor build book.

[whitehause]

Gona have to get a new 7/16 x 14 tap. the one I have won't grab the hole at all. Guess I'll get a bottoming tap for this application

[vandor]

I broke 2 taps doing this. GC said that he has 3 different taps, a starter, a medium and a finisher, so the threads are cut in 3 steps. One really needs machinist grade tools to do this.

[whitehause]

Don't know what he used as the "step up" taps, but it's a bear. I've gotten about 1/4 inch of threads in each one but that's as far as I can get. If I can find some real shallow plugs, I might just loc tite the crap out of em, peen a couple spots at the rim of the holes so they can't back out and call it good.

[whitehause]

Welp, after a night of deep reflection I said screw it and put the hammer down on tapping the holes. Got two new taps and got all 4 holes done with only breaking one tap Luckily it didn't break flush so I could grab it and turn it right out. Used a 3/8 torque wrench and set the torque at about 30 Lb's. When it clicked I would back the tap out, clean the hole and tap, and go back at it. BTW about 45 Lb's is where the first tap finally broke, so I set the second tap at 35 Lb's and kept working it back and forth. Now I just need to find some 7/16 x 14 plugs since my local hardware store didn't have that size.

[beek]

I destroyed 2 taps threading my crankshaft. they were expensive snap-on taps. I feel it is the hardness of the crankshaft that does it, I was determined and finished it and just considered the destroyed taps an expense of the project

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[whitehause]

I got two Irwin taps at the local hardware store. They actually grabbed and cut very nice, well, till I got too aggressive with the first one.
I didn't go quite as deep as you did, but was able to find 3/8th inch deep plugs, so I should be fine. After all, the welch plugs are just thin metal so some loc tite and a couple peens on the lip should be good to go.