Semi race motor advice

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whitehause
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First Name: Tim

Re: Semi race motor advice

Post by whitehause » Sat Feb 09, 2019 9:07 am

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
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Re: Semi race motor advice

Post by fp55scca » Sat Feb 09, 2019 11:04 am

whitehause wrote:
Sat Feb 09, 2019 9:07 am
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.
------------------------------------------
--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.
Jim Scurria
Norfolk, VA

1972 Fiat 124 Spider
1971 Spider - SCCA FP-24
1974 CSA Abarth Replica
1981 Fiat Spider Ratrod
fp55scca
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Re: Semi race motor advice

Post by fp55scca » Sat Feb 09, 2019 11:13 am

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

1972 Fiat 124 Spider
1971 Spider - SCCA FP-24
1974 CSA Abarth Replica
1981 Fiat Spider Ratrod
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friedman
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Re: Semi race motor advice

Post by friedman » Sat Feb 09, 2019 6:06 pm

I'm waiting for Jim's motor build book.
Carl in Virginia
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whitehause
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Re: Semi race motor advice

Post by whitehause » Sat Feb 09, 2019 6:46 pm

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
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vandor
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Re: Semi race motor advice

Post by vandor » Sun Feb 10, 2019 6:56 pm

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.
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whitehause
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Re: Semi race motor advice

Post by whitehause » Mon Feb 11, 2019 5:27 pm

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
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Re: Semi race motor advice

Post by whitehause » Mon Feb 11, 2019 8:46 pm

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 :lol: 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.
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beek
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Re: Semi race motor advice

Post by beek » Tue Feb 12, 2019 10:50 pm

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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2018 Abarth Spider, Daily
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whitehause
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Re: Semi race motor advice

Post by whitehause » Wed Feb 13, 2019 6:01 pm

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.
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