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Discussion Starter · #1 ·
I recently purchased an Accucraft C-19. The engine looks great, but was poorly timed right out of the box. I followed Dave Hottmann's thread, C-19 tuning, no pics


http://www.mylargescale.com/Communi.../1/view/topic/postid/22294/Default.aspx#24739


I Found that it stopped hadr at the 9:00 position on the Left side. I adjusted the eccentrics until it would stop at this location ony when the throttle was turned down, but neverthe less it would still always stop at the 9:00, left side. With the engine upside down, and moving the drivers back and forth, I noticed that the bushings on the connecting rods and side rods were loose beyond any reasonable amount, and deducted that the lost motion between the connecting rod, where it connects to the second set of drivers, the side rod on the second set of drivers, and the side rod connection to the third set of drivers, where the eccentrics that control the valves are located, was enough to throw the timing off, and any amount of adjusting the valves would be futile until this exessive play was removed, thereby cleaning up the motion between the cylinders and the valves. I checked around and located some sealed ball bearings, with 5mm ID x 8mm OD x 2.5mm width. Perfect for the second driver crank pin, so long as you ream out the connecting rod and siderod to 8mm to accept the bearing. Yes there is enough material on the connecting rod and side rod for this. I put thread lock on the bearings as they are pressed into the rods. Then comes the third drivers. that have a 4 mm crank pin. I also got some 4mm ID x 7mm OD x 2.5mm width bearings for this, and this siderod location is reamed to 7mm. With all bearings installed, there is no delayed reaction between the piston and the valve, greatly increasing timing. I planned on adjusting the valves after this mod, but it ran so well, I think I will leave the valves right where they are. I did not put bearings on the first or fourth drivers, because this has nothing to do with the timing.

When you do this mod, you will find out how good the drivers are quartered, and the quartering may need to be adjusted if you experience a hard spot that wasnt there before. Mine was quartered just fine, so i didnt have to do this. This is another reason not to do this mod to drivers not associated with timing, as then you would need all 4 driver sets perfectly quartered, multiplying your chances of creating a hard spot to fix.

Bearings were found at www.vxb.com

part#67422 10 shielded bearings 4 x7 2.5 for $19.00


part#RC85 10 shilded bearings 5 x 8 x2.5 for $15.00



Reamers were found at Enco.com HSS 7mm and HSS 8mm.

Tim
 

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What would be the benifit be of installing ball bearings on the rods and not just making new correct bushings? Adding ball bearings to the axles, now that would make a difference in my eyes.
 

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Discussion Starter · #3 ·
I could of put correct bushings instead of ball bearings, and then replaced them again when they wear out. Its just another way to skin the cat. i even have the bronze rod and lathe to make bushings with. Just thought that the tightness of the ball bearing system was worth the effort to clean up the slop so the cylinders work in unison with the valves.

Tim
 
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