Shadow Build

[John H]

Thanks, sometimes photos say more than words.
I started to ream the valve guides today but the reamer wouldn't cut as it should. It felt sharp and looked sharp but cut very little. I suspect it was used on cast NiResist guides at some point. I will use a new reamer and hopefully get the finished bore needed. If it's close I'll see if I can borrow a Sunnen hone to get it perfect.

[John H]

Scored a valve guide hone, so after reaming to .371 the Sunnen P-180 finished the job. Sure is nice having the right tools.

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The next step was truing the valve seats. A special pilot fits into both the lower and upper valve guides.
This is to make sure the finished valve seat is concentric with both guides.
Next will be cleaning up the taper/scraper end of the guide and installing the guide retainers.

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[Lotus54]

Looks like a nice setup.
Yes- nothing like having the right tools

[ClineDesign]

https://www.cycleworld.com/story/motorc ... Jqavj1Vn7s

[John H]

This story is similar to the last Vincent I rebuilt/preserved. Now in new mechanical condition but looks just as found at a garage sale. Not my choice.

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[John H]

These tools are made to bevel the top of the valve guide and to hit the bevel to make it slightly undersize. This thin sharp edge reduces any excess oil on the valve stem. Too much oil on the intake valve can foul spark plugs as well as carbon up the rings. Excess oil on the exhaust valve can cause carbon buildup on the valve stem causing excess wear and possible valve sticking open of course causing major damage.
Note! The photo shows the lower part of the valve guide. The tools are used only on the top of the valve guide.

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The spark plug threads were marginal so this is the time to replace them. Time-Sert makes an excellent insert that is installed with the special tool kit.

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[John H]

The last step on the heads, other than paint, is mating the surfaces to the cylinders. The head must fit to the top of the cast cylinder liner while leaving .003" gap between the head and the cylinder muff. Since Vincent doesn't use a head gasket the torque from the head bolts is what creates the seal. The .003" becomes .0" clearance. This also eliminates warping or breaking the head. The cylinder liner lip is set nominally at .125" above the muff so the recess in the head is .122". One cylinder was .125" and the other one was .1235" so made the adjustment with the mill.
Still haven't decided what paint process to use. Back in the day, they were dipped in hot stove enamel.

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[John H]

Back to the flywheels. The flywheel is bored oversize to fit main shaft. I gambled on having enough tonnage to press fit .0045 without galling. I will still drill a dowel pin hole, half in the flywheel and half in the new pin just to keep it from ever turning as it did before.

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Now the new drive shaft is locked in a fixture on the mill. The boring head is then located 90mm from the center of the main shaft to the crank pin bore. The std bore/stroke is 85x90. Now the flywheel is bored to fit the new crank pin. It's a heavy press fit also so both flywheel bores must be perfect.

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Before assembly, the new bearing races are pressed in the rods. The small end is reamed and honed to size and the big end is Sunnen honed to a half thou clearance. Nothing here is difficult, just take a lot of time.

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[John H]

Ouch!! The first cut to clean up the original crankpin bore didn't clean up So plan B will be to exchange the new pin for one that is .125" bigger diameter. I went this way on the last crank I built, I understand now why.

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[Lotus54]

Do the big end rods use uncaged rollers?
Good you can get oversize crankpin for a reasonable price.
Was it common for the cranks to get out of true by moving on the pin? Or you just making absolutely certain it will not.

Looking good!

I have two projects I may start soon, not sure which yet.
1. Install four shoe drum, with matching forks on 73 Benelli SportSpecial. It is off the 250 two-stroke road bike, I had one of those new when I was a dealer and the brakes are fabulous. Stock is not so hot.

2. 70 Benelli mini- I got this a number of years ago, went through the ‘ownership in doubt’ (easier then, since local inspection) - and didn’t want to start on it until I got the title. Needs restoration, but all there. Kickstart shaft is sheared, but it runs (or did a few years ago). Might be interesting finding the little street tyres.