PMR 1880'S HORIZONTAL MILL ENGINE KIT

[JRNYMAN2LMAYKER]

I just purchased a casting kit from PMR for their 1880 horizontal mill engine. The castings are top notch and the kit is very complete. I have been studying the drawings and have come upon a situation I found unique to the PMR kits. I was suprised to find that the crank actually runs in the iron casting mains and caps rather than in bronze bushings? ???
I have decided against the supplied cast iron crank casting and am going with either stress proof or 4140. Now in the machinist world we know that 2 like materials running against each other is not really accepted, except for cast iron, which is why the choice for a steel crank. Besides it will polish up better.
My question is should I alter the design to accept bronze bushings or is a steel crank running in cast iron as good or better??? This is the first time I ever came across an engine designed in this manner.

Thanks in advance for any suggestions or advice.

Greg

 

[gbritnell]

The steel crank running in iron would be fine. If you have the room I would make bushings anyway that way if there is wear you could just replace them.
gbritnell

 

[black85vette]

The only factor I can think of is how much you actually intend to run the engine. Most of mine run infrequently for short periods so I can get away with more than the ones that go to shows and run all day.

 

[Tin Falcon]

Many of the PM engines used to made with bronze castings. I think the CI will probably wear fine. So you can make to print and add bushing later if needed or add replaceable bushings later.
Tin

 

[JRNYMAN2LMAYKER]

Thanks guys !!! I have made the decision to go with bronze bushings. This, however, leads me to another question.
The bearing caps are drawn with a .030 step in them for alignment purposes to the bearing blocks. The step is .500 wide which is what I need to increase the journal diameter to allow for the bushings to support a .375 shaft. Are these absolutely essential? The only other alternative would be to move the step width out to a width of .750 and the step will then be located right on the cap bolt hole location. I hope you guys understand what I am trying to convey in regards to this feature. If my memory serves me correct, I do recall having seen engines designed with the step at the hole locations, but.........
Thanks again!!!

Greg

 

[bearcar1]

Greg, have you considered using replaceable bushings instead of an actual bearing block type of arrangement in that application? There isn't a great del of room to work with there as you know. When I did my engine I too thought about bearings but opted to not re-invent the wheel for once and left the shaft running in the casting. As previously stated, it isn't likely the engine will see that much service to begin with. A thin walled 'top hat' style bushing could be introduced in that location if you are dead set on a bearing configuration, good luck. (and don't forget the pictures)

BC1
Jim

 

[JRNYMAN2LMAYKER]

bearcar1, I did mean the "top hat" style bushing versus a seperate block. I am sorry if there was confusion in my explanation. I do not expect to use the engine for anything but display purposes and the occasional run at shows etc... In fact, I will only operate on low pressure compressed air.
I do plan on doing a build thread on her, however, I am on an MANDATORY immense amount of overtime at work and I have no ambition to start until after the Holiday Season has passed. I know, shocking isn't it with the amount of good folks losing their jobs and taking lay offs. It does make me feel a bit uneasy and somewhat guilty. :-[

I want to wish all of you folks a Merry Christmas and a prosperous New Year!!!!

 

[JKAG]

I am embarrassed to say I have an Oilite bearing on one side of my PMR mill engine. An error required boring out one side. I went with the "hat brim" style and put the brim on the outside.

When I take the engine apart for painting, I'll put a matching bearing on the other side.

 

[Mainer]

I'm glad to read JKAG's post and learn that I'm not the only one who has used bushings to correct an error. The first time I bored the bearings for ETW's "Unicorn" I didn't get the alignment very good and as a consequence bored them again, 1/16" oversize, then made a couple of 1/32" wall cast iron bushings to get the final hole diameter correct.

 

[ironman]

I am building PMR 3BI engine (horizontal). I did same as JKAG, drilled one Cast Iron Brg oversize accidentally, took a bronze bearing from a pile of Copy machine parts, bored it to proper size and reamed it for crankshaft and pressed it into oversized hole (top hat to outside). Will do other one in time. Ray

 

[Jadecy]

here is a log of my build of the 1880's drilling engine


http://www.modelmachinist.com/albums/Build_PM1BI/PM1BI_Build.htm

I made thin brass bushings and drilled a hole to line up with the oil cups.

 

[MikeR C]

Don't forget brass-backed babbit bearing shells!!