Killer pinion bushes 25593-52

Production K Models

Killer pinion bushes 25593-52

Postby John R » Wed May 05, 2021 3:09 pm

These engine killer bushes are out there for 52-56 Ks. The repro has everything wrong except outer diameter and bore. The killer is that the groove down the outside on the original is missing on the repro. It's the supply to the end of the pinion shaft for the big-end. The oil hole isn't needed and serves no purpose. The good news is 'they're something to work on', and can be used when modified.
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Re: Killer pinion bushes 25593-52

Postby sportsterpaul » Thu May 06, 2021 12:32 pm

Good to know, thanks for the tip. I will be tearing into my 1952 engine this year, so it is important to me. Major problem is that the cam cover has been chromed. I am pretty sure that stripping chrome off will ruin the bushings. I am thinking I might try to sand the chrome off, if the bushings are OK. They have ruined the cover twice anyway, once by sanding and polishing, and then by chroming it. I am just trying to get the bike running, not do a 100-point restoration.
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Re: Killer pinion bushes 25593-52

Postby Monti » Thu May 06, 2021 4:25 pm

Dear john

Thanks a lot for this information. What does the original pinion shaft look like? Does it have a hole like the ones of the big twin Harleys or does it get the oil from the end of the shaft like the later sporsters?
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Re: Killer pinion bushes 25593-52

Postby John R » Thu May 06, 2021 5:35 pm

Hi Monti, Feed via the end of the pinion shaft, not the side. Big Twins get a shot of oil to the big end once every revolution. K Models get a continuous flow. The Big-Twin oil pump from Pan-Heads up had to send to top end as well as hydraulic tappets. I guess if the big-end got continuous feed the oil pump wouldn't have enough capacity for both.

On Ks, no top end, just a 40thou jet in each cylinder wall. So opposite problem - what to do with the oil supply. Feed it continuously to the big end, not that it needs that much. But a good flow does help carry heat away.

And Paul, I used to work at a plating plant. Yes, stripping the chrome but more particularly the copper will affect the bushes, but hard to say to what extent. You can ask them to put bungs in all the holes, including oil supply holes, or paint the bushes with 'resist'. The ali could end-up looking eroded. Or... if getting it running but you hate chrome, fine grit blast the chrome till it looks matt, if that floats your boat. Or paint!

Pinion bushes can be worn quite bad if flywheels out of true by hard riding. Then most of the oil supply escapes from the back of the bush through the clearance and into the gearcase. Make sure flywheels shafts are running true, and clearance in the bush should be half to one thou. The standard bush reamer is 5/8", so can measure the shaft to check what the clearance would be.
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Re: Killer pinion bushes 25593-52

Postby Monti » Fri May 07, 2021 3:49 am

Hi Jon,

Thanks a lot for this information and your explanation which makes sense for the OHV twins. What about the W and U side valve engines? In these, the oil goes to the crank and the timing gear housing only.
Would it be possible to check the original pinion shaft and let me know what size the hole at the end of the shaft respective the internal restriction (I know that the restriction in the aftermarket shafts has a diameter of about 3/16”)?
According to my knowledge there is no oiling system diagram for the Ks in which one could see the flow of the oil through the K engine. I ask all these questions because I would like to understand the oil circulation of the K engines.
Thanks a lot for your help in advance
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Re: Killer pinion bushes 25593-52

Postby John R » Fri May 07, 2021 4:59 am

Yes, the K's are like the older flat-heads other than the addition of a .040" oil-jet drilling in each cylinder wall, and new-style oil-pump. A Pan-Head diagram is the same in principal other than no oil to tappets and head, that oil just goes to the cylinder jets. The tappets are oiled via each having a drilling to the crankcase - that way oil mist is pushed to them and surplus pulled back due to breather timing.

Can't say if my pinion shaft is original H-D. The main drilling is 3/16" but at the flywheel it reduces down to 1/8", and big-end (crank) pin. I'm unsure but think original pins had just one hole feeding the bearing. Later pins, whether repro or not can't say, have two or three holes.

A word of warning. I have seen repro crank pins (for another model) with the key-way at the wrong end. That would cut-off your oil really good! Never trust anything - check and check again.
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Re: Killer pinion bushes 25593-52

Postby Monti » Fri May 07, 2021 5:59 am

Thanks a lot for checking your pinion shaft and also your warning.
I wonder if somebody still has an original pinion shaft on which this could be checked.
I have actually changed the oiling so that the oil goes from the side into the pinion shaft to the crank (like in the older-flat head engines I haven been working on). I think that this will reduce the bushing wear and improve the cylinder oiling. Furthermore, I think that too much direct oil to the crank pin can be a disadvantage (this is not a plain bearing).
This is just my opinion and there is no guarantee!
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Re: Killer pinion bushes 25593-52

Postby hennesse » Fri May 07, 2021 6:40 am

Out there? From whom would you suggest we not purchase these bushings?
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Re: Killer pinion bushes 25593-52

Postby John R » Fri May 07, 2021 6:49 am

Keep in mind that if flywheel shafts are running true there is no significant load on pinion shaft bush in cover. When I'd trued my flywheels (they came within half a thou), and installed in cases I used engineer's blue on the end. With cover fitted and flywheels turned, removing cover showed only the slightest hint of blue on the bore of the bush (which was the new modified repro bush, line reamed 5/8"). This shows that the pinion shaft runs central in the bush when everything is right, rather than running on it. It 'floats' anyway, so lots of oil isn't vital. Maybe some load on bearing if engine rev'd really high and flywheels flex.

I would say that continuous oil to crank pin plus with that lashing around, plus the oil jets in the cylinders, together ensure that the cylinders/pistons are well oiled as standard. Having said that, I have put a 3/32" metering plug in the end of the pinion shaft. This is more in mind of getting the oil pressure light out at riding speeds below 40mph! I've also given close attention to the oil pump to ensure it's as it should be. A lit oil light is never reassuring. :shock: In '59 Sporty manual, oil pressure at 20mph in top gear is supposed to be 6lbs+ . I can dream!

Some say that too much oil to the crank bearing can make rollers skate. All I can say is that on my used motor the rod fit was fine and everything looked very healthy when stripped, so reassembled with same parts.
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Re: Killer pinion bushes 25593-52

Postby John R » Fri May 07, 2021 6:53 am

Who has the bad bushings? Just enter in Google - Harley "25593-52" - (use the quote marks) and straightaway you will see some of them, starting with The Good Old Motorcycle Parts Company. Not blaming anyone in particular.
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