Double Trouble

If in doubt, or it doesn't seem to fit elsewhere - put it here.

Re: Double Trouble

Postby John H » Thu Mar 11, 2021 8:55 pm

After polishing off the welds and rechecking the balance 13g was removed and now I have two cranks that are perfectly matched. Still waiting for new con rod bolts and nuts and a second set of standard rod shell bearings. They were within spec but I decided to go all the way.
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Re: Double Trouble

Postby ClineDesign » Fri Mar 12, 2021 10:24 am

I keep wondering how much longer that engine would have lasted if John had built it originally. Thanks for posting all the photo of your craftsmanship!
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Re: Double Trouble

Postby John H » Sun Mar 14, 2021 8:18 pm

Jay, back in the day these engines were cheap and rebuilt with a limited source of aftermarket parts which weren't much better than factory parts. Today most all the parts are available in high grade materials, better lubricants and fuel. I don't remember who is responsible for the phrase "gas is for washing parts, alcohol is for drinking and nitro is for going fast". Nitro is also for destroying a lot of parts. Only a few racers back then tamed the stuff well enough to win races consistently.
Hope to have it finished this summer, maybe in time for a bbq??
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Re: Double Trouble

Postby ClineDesign » Sun Mar 14, 2021 10:56 pm

Would love to photograph it when complete! And at the BBQ.
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Re: Double Trouble

Postby John H » Tue Mar 16, 2021 10:05 pm

Sure thing Jay, photos would be great. BBQ ?? We'll see if we can make that happen too.
The rod bolts came today so dry-fit all 4 with plastigauge to check clearance. Glad I did as one was too tight on one edge. I dressed it with a bearing scraper to get the clearance needed. Next will be fitting bearings and cases.
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Re: Double Trouble

Postby John H » Sat Mar 20, 2021 9:12 am

Started to assemble motor #1 only to find there wasn't any end-play on the crank. I'm guessing it was caused from welding the reinforcing plates around the drive side main bearing. I had two choices, bore the main bearing area deeper or reduce the thickness of the main bearing outer race. I chose reducing the thickness of the bearing race by .006". That gave me .003"end-play which is within tolerance. Motor #2 will be checked for sure before assembly starts as I replaced the outer part of the crankcase.
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Re: Double Trouble

Postby John H » Mon Mar 22, 2021 10:19 pm

Made good progress this weekend. I was concerned that after resurfacing all the mounting lugs on the cases there would be some interference problems, and there was. The motor plates are now .080" closer than before so the tube spacers and the front frame member need to be narrowed by .080". The rear frame member will require two 040" spacers to go between the motor plates and frame lugs.

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The sump plates and brass screen plate also required narrowing.
Next up will be weld repairing the ring grooves in the cylinder wall.

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Re: Double Trouble

Postby John H » Sun Mar 28, 2021 11:18 am

This project came with two sets of cams. One is Harman & Collins and the other is Norris. Both were popular back in the day and were offered in several configurations. I decided to go with the Norris "D" grind set which is almost new.
My next problem is that the tappets are in such condition they would damage the cams. So I had to make a tool to regrind the tappet profile. Triumphs have two different radius specs depending on which cam is used. In this case, the "R" 1-1/8" radius is required. The other radius required is 3/4". I modified a jig block and made a shaft to hold the tapped while adjusting the radius / arc needed. The surface to be ground is carbide so took some extra time to grind all 8 tappets.
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Re: Double Trouble

Postby John H » Thu Apr 01, 2021 7:16 pm

I've been trying to time these Norris cams based on information in their book. Finally realized they were marked wrong. So now it's a guessing game as to what settings they will run best.
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Starting with 'valve lift' and duration the options narrow. Here is a copy of a cam profile from the valve timing program. I will be calling someone who really knows this stuff to get firm numbers.
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Re: Double Trouble

Postby John H » Fri Apr 09, 2021 7:43 pm

I spoke with Jim at Megacycle today and got the numbers I needed. Lobe centers will be as close to 105º as possible. To get accuracy for maximum performance is some instances offset keys are used. I will do the fine tuning at the valve adjustment.
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