Double Trouble

[John H]

After nitro engines have been run the oil is contaminated by getting past the rings, so it's usually
changed after every run. Also part of this process is purging the fuel system with with a less caustic fuel.
Drain plugs are added make this process easier.

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[John H]

The bearing bore is now centered perfectly on the cam so next step is to plug the fuel pump mounting holes and move them so the pump shaft will be centered too. I should have done this before finishing the bearing bore but got ahead of myself.

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[Lotus54]

I certainly appreciate all these posts. Including mentioning when you do it out of order, or find unforeseen issues.
Great stuff.

[John H]

Thanks Mark, We all make mistakes. Today was another one too. I drilled out the old pump mounting threads, heated up the cover and started to plug weld the holes only to find a huge amount of old oil in between the original timing cover and the round pump flange that had been welded in place years ago. I machined 3 plugs and pressed them in place and then welded just around the surface just enough to be sure they will never move.
Next problem happened when I was machining down the welds and relocating the counter bore and the carbide insert in the boring head came loose and dug into the cover. I've never had that happen before but it came close to a disaster.

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[John H]

The cover with the new bearing is finished. While still set up in the mill to drill and tap the 3 mounting holes for the old style fuel pump I decided to add 3 additional holes for the new hex drive pump. I have not yet find anyone who will flow test the old pump so may have to use the new pump after all. It just doesn't look correct on a vintage machine.

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[John H]

I did final inspection on both engine cases, cleaned them in white gas and then cycled them in the dish washer. They really look nice. Next step will be checking the balance factor on the #1 crank. I can tell from the extra drilled holes that it has been re-balanced, hopefully in the 85% range. The #2 crank is heavier so will probably need re-balanced. These 800cc pistons are quite a bit heavier than the original 650cc pistons so re-balancing is important.

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[John H]

The flywheel on the engine #1 appears to have been balanced different than #2. Rather than guess the balance I'm will make a pair of Bob weights. Triumph factory made these for 650 and 750 cranks to get a balance factor of 85%. The ones for the 750 were 689gm each so that's what I will go for. I scored a nice piece of 3x3 bar with a 1-1/2" hole through it. It was bored to 1.625" to clamp to the rod journals with pinch bolts.

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[John H]

The 'bob' weights are finished along with an assortment of small add on weights that can be used for fine tuning you might say. Starting with the setup Triumph would have used on the 750 engine I see crank from motor #1 isn't even close to 85%. This crank also has counter weights welded to the flywheels which cause some of the problem, I think. I'll know more after talking with someone who has balanced many Triumph motors.

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[John H]

With all the calculating done, I'm convinced that crank #1 was electronically balanced and checks out at 84.8% BF. It is the one with welded on counter weights. Crank #2 checks out at 62.7% BF. What's interesting is that both cranks weigh within 4oz of each other. Now the decision has to be made to add weld on counter weights. I want both engines to be happy running together, if they ever run, but is this an exercise in futility or just having fun. Maybe both.

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[John H]

Cut out matching counterweights from 11ga stainless I just happened to have. Welded them in place and peened the weld good before polishing out. All went well and back on the knife to see how close it was, 13g light. Not bad.

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