Finding Top Dead Center, Seca Forks, And Prospector Problems


 Keith Fellenstein Tech Corner

Finding top dead center

Q: I’m having difficulty setting the timing on my Boyer-equipped 1966 Triumph Tiger T100SR. I’m using a Motion Pro degree wheel that measures 6.75 inches. I set the timing at 38 degrees BTDC as per the shop manual. No joy! I have also tried 19 degrees BTDC thinking of exhaust cam rotation. It’s been decades since I’ve done this, what am I missing?

Randy Randall/via email

A: It depends on where you have mounted the degree wheel. If you have it mounted on the crankshaft, the 38-degree measurement is correct. If you have it mounted on the camshaft end where the points cam sits, you cut that in half to 19 degrees. The best way to find exact TDC is by use of a piston stop or dial indicator. The piston stop is a rod that protrudes deep enough in from a spark plug sized adapter to stop the piston before it reaches TDC. You fit the degree wheel and stop tool and rotate the engine forward until the piston lightly reaches the piston stop. Make note of the position of the degree wheel and then rotate the engine backwards until the piston once again reaches the stop. Note the position of the wheel once again. TDC will be exactly between the two measurements. A dial indicator works also. The only problem is fixing it to the head in some way. Motion Pro sells a kit they market for 2-strokes, but I see no reason why it wouldn’t work on 4-strokes as well. It mounts in the spark plug hole. With a dial indicator you rotate the engine until the pointer reaches its highest point and then rotate the bezel to mark that as zero. Repeat a few times to home in on exact TDC, then use the degree wheel.

Seca forks

Q: I’m the original owner of a 1982 Yamaha FJ650R Seca. I resurrected it about 3 years ago after storing it for about 25 years. I love riding it again. The problem that I’m writing to you about is the uneven appearance of the front forks. It looks like some of the coating has worn off. This area can be polished, but the rest of the fork remains dull. I don’t care if the fork is bright or dull, but I would like a consistent finish. Do you have any suggestions?

Rich Borden/via email

A: Those forks were originally clear coated and the coating is worn off on most of the leg. The only way to get a consistent color across the entire leg would be to remove the rest of the clear coat, either with stripper chemicals or with steel wool. After it’s all removed you could then polish the whole leg to get a consistent shine. I’ve never found a way to reapply a good clear coat from a rattle can. After all that work, you just have to polish and wax it often.

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