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Thanks for the comments everyone.

...So, just check if yor chanels are communicating and should be ok.


I guess that is what I was asking about, especially for the oil channel in for the crankshaft gear oiler. I just can't tell if the hole is supposed to be fully drilled out, or just barely opened up to the channel cut around the circumference of the hole in the block (like it shows in the picture). Based on the machining and casting of the block, I would not be surprised if it was improperly drilled from the factory.


How snug is the fit between oil pump gear shaft and bush? Wear in either? Can you pull that bushing, rotate and press it back in?

...looking forward to the results of your cylinder work. Are they honing ore boring?


I am thinking of driving it out, turning it, and driving it back in. Or just leaving it. I think it likely fine the more I look at it.


I just got a call from the machine shop today. The cylinders should be done tomorrow. He bored them to a .09 mm clearance on the piston which falls right in line with the 0.08 - 0.10 mm clearance spec I've been quoted. He also end-gapped the rings for me...what service! I'll post up same pictures when they're back.

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In regards to oil flow one cylinder is partly lubricated by the oil pump.


The passage for the oil is between the lower cylinder bolts, and one should notice that this doesn't always line up with the hole in the gasket - so this should be checked and the gasket cut to correct if it's not there.

The oil is supposed to run around the cylinder in a groove there and enter the valve area, and then go on the top of the piston through 3 holes.

You can see this on the lube chart too.


NEVER use liquid gasket on the bottom cylinder gasket.


(I'm only mentioning it because it's happened to people before that they don't notice this particular oil passage. And I think I actually burned a piston because if this when I was a K750 newbie back in 2011)

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  • 2 weeks later...

I drove the oil pump drive gear bushing out to Rotate it. On closer inspection the inside is pretty trashed.


Does anyone know where to get a new one? Looks like it’s steel which is weird - I would have expected bronze.


Any suggestions?



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That's a good link. I can't believe I've never seen that site! Unfortunately, they do not have that particular bushing (P/N 7201106). In fact, no one seems to have that part. Ural-Zentrale, Old Timer, Holopaw, East Highway...nothing.


The inside of mine is badly galled so I'd hat to have to reuse it.


Anyone have any ideas?

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  • 7 months later...

Hi Folks, I am back at it after about 7 months of school and work taking up all my time.  So, looking at my newly cleaned up cylinders at Autosport Seattle (awesome shop), and took the advice to just drive in a new bushing.  It's a steel bushing blank that I chamfered and drilled to match the original and that looks pretty good. 

Now, I am working the piston rings.  Unfortunately, I think I need some new rings.  

The gap on the left looks good.  0.55 mm gap (measured 25 mm down from the top of the cylinder).  The right side though is 0.75mm which I read as out of scope - too big.  I haven't messed with them, so maybe they shipped me a set for a different bore or something.  Has anyone seen issues running a ring gap that big? 

The other issue is that my pistons came with no directions on ring installation.  Here's what I have.  What order/direction do they go? 

First off, I think this is the order of rings from top to bottom (right to left in picture): Chrome, stepped black, oil, then oil2s.jpeg.60d12c826b93c260edb10599e72dd67e.jpeg

Then, if that's the right general order, which way is up on these rings?  They are asymmetrical. 

Here's the black ring, which I think is second from the top of the piston: 


 Here is a close up of the oil ring:


And here's a profile diagram of the rings.  Again, which way goes up?


Thanks everyone, trying to get this ting back together!

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  • 1 month later...

A pity I didn't see this thread when it started. I have C hang Jiang high performance pistons in my K750. I lightly honed the cylinders and threw them in. Better compression and much less oil consumption. They have much thinner rings. I would suggest it is not worthwhile going for exact clearances on the sidevalve motor due to the way the cylinders distort due to heat.

If you want to make a big difference then attack the ports with a high speed grinder and burr. Removing the sharp edges and streamlining the ports reduces the heat take-up from the exhaust gas plus it gets the hot gas out quicker. This makes the engine run cooler.

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