Cylinder Oil Line Screw

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Cylinder Oil Line Screw

Postby JerrryR » Wed Dec 08, 2021 9:00 pm

Hi All, I'm looking for your thoughts on something I ran into today, what you can tell me about why it exist and finally how should I proceed. It has to do with K model cylinders and their Cylinder Oil Line Screws. See picture below.

Cylinder Oil Line Screw, 16890-52, 52-56, #1.jpg
Cylinder Oil Line Screw, 16890-52, 52-56, #1.jpg (67.45 KiB) Viewed 1599 times

I had a pair of 54KHK cylinders sleeved, they were about .120" over and had been running stock Indian Scout pistons. The rods had even been polished. The shop that sleeved the cylinders even commented on the cylinder work that they could tell had been done. What they forgot to do though was to drill the cylinder oiler hole through the new sleeves so I set out to do it. What I discovered was that the oil hole screws were so long that they appear to be blocking off the oil feed hole coming up through the base of the cylinder? I grabbed a set of 56 cylinders and checked their screws, they were both short and would appear to let oil flow. I then grabbed a set of 52 cylinders and checked their screws, they were both also short, same as the 56. I did not check the 56 cylinders to determine if they were KH or KHK cylinders. See below pictures.

Cylinder Oil Line Screw, 16890-52, 52-56., #2.jpg
Cylinder Oil Line Screw, 16890-52, 52-56., #2.jpg (312.55 KiB) Viewed 1599 times

Cylinder Oil Line Screw, 16890-52, 52-56., #3.jpg
Cylinder Oil Line Screw, 16890-52, 52-56., #3.jpg (321.37 KiB) Viewed 1599 times

I have heard some discussion from folks that these oiler holes were unnecessary and even affected performance? So I guess my questions are as follows:

Why would someone want to block off this oil hole?

Were the cylinder oil hole screws for all KHKs the long blocking version?

Should I drill the holes in the 54KHK sleeved cylinders and use the shorter screws?

Thanks for your thoughts and Happy Holidays to you all.
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Re: Cylinder Oil Line Screw

Postby wz507 » Thu Dec 09, 2021 1:20 am

Regarding the correct screw to cover the piston squirter drilling in the cylinder, the factory part is a short ¼-28 fillister head screw (as you found in the early and late cylinders), with a generous relief just below the head, as shown below, and a complimentary brass or copper washer. When this screw is fully seated it does not enter into the oil gallery. It would make no sense to employ a longer screw than this, as you would clearly not want the screw protruding into the drillway and impeding oil flow.

piston squirter srews.jpg
piston squirter srews.jpg (27.5 KiB) Viewed 1567 times

The hole in the cylinder is obviously an early attempt at making a piston squirter. However, a jet of oil at the bottom of the cylinder oriented across it, is an example of an early, poorly designed piston squirter. Modern piston squirters, found on 4 stroke motocross, hog and most automotive engines direct the oil jet straight up the bore where it impinges on the piston crown to cool it, lubricate the cylinder, and carry heat away.

KRs had no piston squirters (but ¼-speed oil pump), but they were shorter stroke than a KH so shorter cylinder to lubricate, and they seemed to survive just fine. Likewise, all the consumer K Models with ½-speed oil pumps and piston squirters survived well also. Whether you choose to use the piston squirters or not, the full oil pump output ends up in the bottom end of the engine case and has to be scavenged out regardless of how it got there. With the piston squirters, the oil pump output partitions between the piston squirters (2 x 0.040” holes) and the pinion shaft (1/4” dia entry hole restricted down to 0.134” dia where oil exists the pinion shaft). The crank shaft is basically a centrifuge, so even though the pumped oil is under pressure it is also assisted through the crankshaft via centrifugal force, so the crank can accept lots of oil easily. In the absence of the piston squirters the full oil pump output is sent solely to the crank pin, and cylinder/piston oiling occurs via crankpin/connecting rod sling. Regarding partitioning of oil between squirters and crankshaft, given the fact that the crankshaft has significantly larger oil passages than the piston squirters, is closer to the pump than the squirters, thus sees more oil pressure than the squirters, and that the crankshaft also has centrifugal force working in its favor, it would be my opinion that the major fraction of oil pump output goes to the crank even when piston squirters are active.

Pinion shaft end.jpg
Pinion shaft end.jpg (22.47 KiB) Viewed 1567 times
Pinion shaft oil exit.jpg
Pinion shaft oil exit.jpg (16.27 KiB) Viewed 1567 times
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Re: Cylinder Oil Line Screw

Postby Tim The Grim » Thu Dec 09, 2021 10:02 pm

Excellent post Wz507.
I had my cylinders sleeved and chose to drill the oil squirter holes.
It was that way from the factory so I replicated that.
I have always knife edged and turned shallow grooves on my skirts to keep more oil there and splashing up inside.
Mine have the short screws and washers as pictured in Wz507’s photo.

Someday it will run again. Hopefully sooner than later.
54KHK (Current Build),2013 XL1200V “72” Hard Candy, 97 Honda Valkyrie
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Re: Cylinder Oil Line Screw

Postby panic » Fri Dec 10, 2021 10:49 am

It oils the skirt, as did the rocker drain in 1953-* big twins.
The poor design is "what you can do at almost no expense" to make up for the lack of front cylinder baffles used on the base 45 engine.
The KR crankcase interior is a hurricane of oil mist and droplets in the RPM range of use, which is what kept early 2-strokes alive for many decades.
[url=""]The Linkert Book[/url]
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