Double Trouble

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

Re: Double Trouble

Postby Lotus54 » Thu Sep 02, 2021 1:38 pm

Always lots of projects to finish!
I’m trying hard to not start another until the sei is done (or at least mostly done).

I am speculating that you would like to be able to start it up and run, but not race?
1974 OSSA Explorer- 78 Benelli 750 sei, 73 Benelli 250 SuperSport, 68 Benelli Dynamo trail, 76 OSSA GPII Phantom, Beta XTrainer 300, 2020 Electric-Motion Escape ‘R’
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Re: Double Trouble

Postby John H » Sat Sep 04, 2021 11:28 pm

More projects than I'll ever have time to finish. Maybe that's what keeps us active. The Double was originally going to be for show but once I got into it I knew I had to hear it had to run. Will it ever see the drag strip? I don't think so. Pistons are unobtanium unless special made. Had to draw the line at some point.
For the Vincent race motor, CP charged $700 for programing and two pistons and another $300 for two additional pistons.

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Re: Double Trouble

Postby John H » Sat Sep 18, 2021 10:53 pm

The Double got some attention today. After soda blasting the heads I noticed a crack where the intake manifold attached to the head.
Crack.png
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The old weld was removed and the head pre-heated to 300º to cook out any oil that might contaminate the weld. It went well until a sudden puff of black smoke and what appeared to be some type of epoxy came out. More cleaning, grinding and welding. Not pretty but will have to do. The valve guides have now been sealed off in preparation for vapor blasting.

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Re: Double Trouble

Postby John H » Tue Sep 21, 2021 8:14 pm

I set up the rotary welding turntable to hold the scrap cylinder and made a few test welds in preparation for repairing the extra cylinder that has grooves caused by rusty cast iron piston rings. Once I start the silver brazing I don't want to stop until the groove in the bore is filled. I can control the rotation and speed with the foot pedal which lets me concentrate on the weld. Temperature is pretty critical since the repair is close to the flange that was furnace brazed in the fabricating process. The silver I'm using melts at 1100º to 1200º so the preheating and welding should go quickly. I spread the flux paste which you can see and will leave it overnight to hopefully kill any rust deposits I may have missed. Will give it a go tomorrow.

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Re: Double Trouble

Postby John H » Wed Sep 22, 2021 9:10 pm

The silver brazing went well. I did miss one small spot but overall it will clean up ok. I machined off the excess material to within .002" of the original bore, using a carbide cutter due to the crystalized flux.
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Chipped off the remains of any flux then used a bearing scraper to take the weld down to the original surface. Next will be honing the bore to the final finish. Glad this part is finished.
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Re: Double Trouble

Postby Lotus54 » Wed Sep 22, 2021 9:14 pm

Wow- looks great! Great way to salvage those cylinders.
1974 OSSA Explorer- 78 Benelli 750 sei, 73 Benelli 250 SuperSport, 68 Benelli Dynamo trail, 76 OSSA GPII Phantom, Beta XTrainer 300, 2020 Electric-Motion Escape ‘R’
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Re: Double Trouble

Postby John H » Sat Sep 25, 2021 8:59 am

Next job will be honing the cylinders to fit the pistons. The trick will be getting the bore round again without going oversize.
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Re: Double Trouble

Postby John H » Tue Sep 28, 2021 10:14 pm

Unable to find a long 3" x 12" Sunnen mandrel that would be ideal for truing up the bore, next best is to use a vertical cylinder hone machine with an 3" x 6" extra wide stone set. This should help to get the bore round again without going oversize.
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Re: Double Trouble

Postby John H » Fri Oct 01, 2021 9:17 pm

The cylinders are finally finished and turned out better than than I had hoped for. With the right tools in the right hands the bores are now straight and round.
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Re: Double Trouble

Postby John H » Thu Oct 07, 2021 9:30 am

A milestone reached! All major components in house. I picked up the heads from Mark who vapor blasted them and they look great. Next step will be setting up the valve train. Lapping the valves, measuring the valve springs for seat pressure and coil bind and shimming so are equal. It would be nice to use new beehive springs and keepers here. The fact is these motors will never be run hard so will stick with stock springs.
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Last edited by John H on Sun Oct 10, 2021 6:54 pm, edited 1 time in total.
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