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Purple Power 421 Serval


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Figured i would make a post on here after lurking for so long. Quick recap before getting into the details. Picked this bike up about 2 years ago when i was living in detroit. Bike allegedly had a fresh rebuild from a snowmobile shop up north and overall was in great shape. Picked up on a Monday night and first time really riding it was 4 days later at silver lake. Did a bunch of trail riding up in Grayling and at Mound during my time living up there.

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A few months later i moved down to Dallas and mainly rode trails throughout north texas and LSOK as well. Added Alba LT arms, Elkas, and a set of T6s too.   

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This past March, after about 120 gallons of fuel through it, i had a piston skirt shatter which commenced the current build. 

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Bought up a bunch of stuff from blackandyellowbanshee and been collecting parts for a Serval build. 

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Current setup includes Serval cylinders with a play port from FAST, Cases port matched by FAST, 24CC pump gas domes, 35MM PWK, Shearer inframes, VF4s, chariot basket/DD lockup, and a CAMATV promod. 

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Frame has decent powdercoat on it right now so i changed all the bearings, added chain slider kit from modquad, and cleaned up the frame by removing all the unneeded brackets. Also cleaned up the harness and added some nylon braided sheathing. This winter i will reinforce the frame and do fresh powder but i want to shake this setup down before the BHQ ride. 

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Crankshaft is the final piece to this puzzle before assembly but the one i received has some visible runout on the inner flywheel web and after measuring the width it was way out of spec (.025" of variation on web thickness). PTO side was also out of spec based on the clymers however only varied .002" when measuring in 4 spots each 90*. Welds on the pin for the flywheel side also had visible cracks about 60% of the way around and i could catch a fingernail on them. I am suspecting it was pressed together following welding and something got fucked up or it was supported incorrectly. Working on getting this resolved from the source and then i can slap it all together. 

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I rebuild a lot of cranks , those are very common on start/stops with either too much or not enough heat on the tig


I see, do you consider the cracks acceptable then? Curious on your opinion regarding the variation in the crank web width as well. Measurement B below varies from 2.111” to 2.126” on Flywheel side (side with cracks) and is 2.131”(+-) .002” on PTO side . Checked in 4 spots using a dial caliper.


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IMO no it’s not but I’m a lil bit anal. I’ve seen plenty worse than that sent out the door. They probably welded the pin , it walked from the heat then they tried to squeeze it back. What are you using to support the crank? It’s very critical when measuring. Once you get good at it you can leave it .002-.003 out and use the tig to walk it back true .

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Thanks for the input! I have not measured runout as i need to to grab my dial indicator from work. I also have a set of vblocks i will use to support the outer bearings. When spinning the crank in the cases i could see the inside web on the flywheel side wobble when compared to the edge of the case. Thats when i measured the thickness per the cylmer (measurement B) using a caliper (a nice one made by central, not some HF junk).


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When measuring runout support the center bearings only. That’s how I assemble and true them , working from center out both ways. I have a legit true stand from k&l but realized real quick that wasn’t the way to do it. If you support the outers and bring it within spec 0-.002 your center will jump that.002 and vibrate like a son of a bitch. Long story short support the center and work out 

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Can you post the pics here of how you do it? We have some vblocks and a granite table at work. I figure with the bearings on the v-blocks, i can use our test dial to see run out. The test dial measures in .0001" increments. We use them to check run out on some lathe work.

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21 hours ago, sleeper06 said:

If you want pm your cell and I can send you pics of the rig I use. It’s a lil unorthodox and I don’t feel like listening to the trolls. There’s more than one way to skin a cat

I get shit on at work for unorthodox methods. I get shit done, all that matters....

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Shipped my crank back today and they will be taking care of everything and getting one back to me asap.

Getting the chassis ready, bypassed the key and OEM kill switch and wired in the tether. Everything was done with crimped butt splices to avoid any issues from vibration. Broke out the good stuff on the tether wiring too!! Last year i had a bunch of random bogging issues due to the 6 pin connector near the radiator which i resolved using a ziptie to clamp the connector shut.

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Once the bike is up and running i plan on doing a CDI relocation and building a harness using all new tefzel wire and new connectors.


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Claude- I don’t do whatever I want measurement wise. I go by the book and a lil better. The different jigs I have to get the job done are not orthodox compared to a crank shop busting out 100s of these things. Same result different approach 

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