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Sounds like yer good to go then..

In my Experience... pistons are inexpensive, and a Commodity that can be recycled [if new] to someone who needs your particular size... but.. I have not sourced Dnepr Parts like the pistons..

Course... I do Not know any [Worthwhile] Shop around me that will bore and hone a Cylinder ...without Specs, and the piston in Hand...

Go to a Good... old, Greybearded, Independant shop for Harley, or British bikes...and talk to him about Piston clearance etc....

Cast piston is different from Forged..and the Ring Gap is as Important as any "measurement"..

In some instances... a bit More Piston clearance is a good thing... But, Not always...

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If you are looking for another .03mm clearance to bring this to .09mm total clearance than I wonder if honing is the way forward and if you have considered trying this yourself, or if the machinists would do this for you.

 

To take only 0.015 mm of a cylinder wall (.03mm total) would require that the cylinder is set up for boring in pretty well the exact same position as it was the first time it was bored, I don't know how possible this is. Then the cylinders will need to be honed again and a bit more material would be taken off. Maybe there is a risk that you will finish with more clearance than you need for those pistons.

 

Anyway, keep posting and let us know what you find out. Interesting thread. ND

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Thanks guys. I definitely don’t feel qualified to try this myself. Unfortunately I’m traveling for work and can’t make the rounds this week. There are some good shops up here near Seattle that work airheads I’ll see what they recommend. Could just be a quick home, but I’ll leave that to the experts!

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  • 2 weeks later...

OK. Cylinders are at the machine shop getting bored to the correct clearance. They should be back next week. In the meantime, I am looking over the block. I was looking at the oil passages and saw two areas of possible concern. Looking for some advice on these.

 

First, in the oil pump gear bushing, there is an oil hole that passes through to a small gallery. The existing bushing has a hole, about 1mm, maybe 1.5 mm, but it is well off center. i am assuming that is not that big of a deal, but the hole is basically at the very edge of the gallery. Does anyone have any input on making that opening a little larger?

 

 

 

1

 

2

 

3

 

4

Second, in front crankshaft bearing housing, there is a small oil tube that drips oil onto the gears. That small tube is fed from a channel cut into the block, with a weep hole cut into the channel from the face of the block. The weep hole in my block is not cut thorough the full depth of the channel. It results in an opening of only about a 1 mm x 2 mm oval. Same question...should this be enlarged or should it leave it well enough alone?

 

A

 

B

 

C

 

Thanks!

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In my personal opinion...if this was a Ural... increasing the size probably would not matter... on a Dnepr, however, they Operate on oil Pressure... ie the bottom end is suspended in high pressure oil... like a Car... the Ural is most like a Harley... Not much pressure at all...and dependent on Flow...Not Pressure..

Now...again, my opinion.. position, not Size, is important when looking at a pressurized system, and my biggest concern would be maintaining Pressure, while increasing the Volume by increasing the Oil passages size!!

bigger hole = less pressure...IMO...Keep making the oil delivery holes bigger, and risk the pump becoming unable to maintain required Pressure on the Big End....

I would Study the oiling system very carefully before I modified anything!!!!! ie Ensure the Big End, lubrication is Not affected!!

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Thanks Racepres, that's what I was concerned with. It's a Dnepr and I do not want to reduce the pressure by opening up orifices. However, if they just "forgot" to fully drill out these oil passages...I wouldn't be surprised.

 

Really, I don't plan to do anything unless anyone knows that they are supposed to be drilled differently from the factory.

 

Thanks again for your comments. It helps to know I am on track!

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I do believe you are on track... somebody who knows the system intimately, may be able to show us what safegaurds lower end Pressure, such that we can modify other parts of the system... That somebody is not me... but if you stay on track...it may well become You!!!!

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The russian side valve engines have the same principle lubrications as the Ural 650 engines, they don't relies on oil presure but on the flow and the oil mist. There is no significant difference between M72 engine and K750 engine. So, just check if yor chanels are communicating and should be ok.

 

Here is the lubrication chart:

 

post-43591-0-90300400-1579457468_thumb.jpg

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The russian side valve engines have the same principle lubrications as the Ural 650 engines, they don't relies on oil presure but on the flow and the oil mist. There is no significant difference between M72 engine and K750 engine. So, just check if yor chanels are communicating and should be ok.

 

Here is the lubrication chart:

 

post-43591-0-90300400-1579457468_thumb.jpg

 

You saying the Dnepr has Roller Bearing bottom end????

Mine does Not!!!!

All insert bearing bottom ends that I know about require more pressure than flow...while Roller bearings are certainly a Flow thing...

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You saying the Dnepr has Roller Bearing bottom end????

Mine does Not!!!!

All insert bearing bottom ends that I know about require more pressure than flow...while Roller bearings are certainly a Flow thing...

 

No, I am saying about the side valve engine (750cc engine) has roller bearing and needs only oil flow. Dnepr is not side valve engine,it is 650cc and it has shell bearings which operate with high presure oil.

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You saying the Dnepr has Roller Bearing bottom end????

Mine does Not!!!!

All insert bearing bottom ends that I know about require more pressure than flow...while Roller bearings are certainly a Flow thing...

 

No, I am saying about the side valve engine (750cc engine) has roller bearing and needs only oil flow. Dnepr is not side valve engine,it is 650cc and it has shell bearings which operate with high presure oil.

 

Oh... I guess I did Not know that the Flathead is Different!!!

Apologies!!!!

@Afcope

Please disregard my Insert bearing concerns...Rollers are very forgiving, and Will Benefit, from flow increase...ensure you do Not remove/divert too much "flow" from the bottom end..

Note, that on a hot rod Harley [Roller bearings] restricting flow to the top does Not affect lubrication/longevity..

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