Author Topic: Senft "Poppin" engine  (Read 24503 times)

Offline b.lindsey

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Re: Senft "Poppin" engine
« Reply #30 on: March 14, 2018, 05:59:29 PM »
Graphite piston and CI cylinder worked well on mine Brian, but yes no oil needed if using graphite.

Bill

Offline Zephyrin

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Re: Senft "Poppin" engine
« Reply #31 on: March 14, 2018, 06:30:02 PM »
everything is going well and fast too, Brian, nice thread !
Poppin is a great plan, and a fine runner. Very useful instructions in the full paper by J. Senft.
a water cooled version do exist also, with a hoper instead of finned cylinder. your cylinder looks great.

Offline NickG

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Re: Senft "Poppin" engine
« Reply #32 on: March 14, 2018, 06:55:26 PM »
Same experience as bill, it worked well and no lubrication needed. If the engine hasn’t been run for a long time, you can feel the graphite lubricating the cylinder when turning over for the first few times. Then can audibly hear the suction of the piston against the valve. With your experience of both cast iron and graphite giving the same results I’d say either should work just as well. Suppose graphite has the advantage of being lighter too for the reciprocating assembly. I can’t remember on the plans how the gudgeon pin is, I just milled a slot in the graphite cross drilled and made the pin a tight fit in the rod and sliding fit in the piston. Also made it say 1/32” short on each side so it would never scrape the bore.


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Offline Tennessee Whiskey

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Re: Senft "Poppin" engine
« Reply #33 on: March 14, 2018, 08:57:42 PM »
Hey you old hot rodder, I’m following along with you. I’ve seen and heard Bill’ run and when it’s doing it’s thing, the audio is awesome.

Whiskey

Offline Brian Rupnow

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Re: Senft "Poppin" engine
« Reply #34 on: March 14, 2018, 08:57:48 PM »
Not a great deal done today, as I had a few hours of "real" work. I did however manage a pair of flywheel hubs and their accompanying nuts. (I cheated on the nuts---took a pair from my tool-chest and thinned them down on the lathe.) I have never seen flywheels made this way before, but it seems to work okay.

Offline PJPickard

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Re: Senft "Poppin" engine
« Reply #35 on: March 14, 2018, 09:07:24 PM »
Brian,

I made my piston from graphite, but I thickened up the walls on the sides and the end. If you do the same make sure you account for the the difference in length of the, either con rod assembly, or the attachment inside the piston for the con rod.

Offline Brian Rupnow

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Re: Senft "Poppin" engine
« Reply #36 on: March 14, 2018, 10:13:54 PM »
Thank you PJPickard. I plan on using graphite as well for my piston and will take the lengths and wall thicknesses into consideration.---Brian

Offline crueby

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Re: Senft "Poppin" engine
« Reply #37 on: March 14, 2018, 10:41:55 PM »
Neat setup on the flywheels, thats a new one!

Offline Brian Rupnow

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Re: Senft "Poppin" engine
« Reply #38 on: March 15, 2018, 12:15:51 AM »
Not a criticism, but an observation. Nothing shows up worse on a model engine than wobbling flywheels. When I make flywheels I generally leave a bit extra on the width and the diameter so that I can mount the finished flywheel on the correct size of arbor and give them a final "dressing" on the lathe to ensure that they are not wobbly as they revolve. Making flywheels with separate hubs that are not in any way "keyed" to the flywheel doubles the effort required to have the flywheels run true on the finished engine.

Offline PJPickard

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Re: Senft "Poppin" engine
« Reply #39 on: March 15, 2018, 01:24:34 AM »
Brian,

I usually have nothing to complain about Dr. Senft's designs, however I do not like his flywheel solution in this case. I made mine to print, but exactly like you I leave a bit on the diameter and sides to clean up. And in this case I'm glad I did as they need a finish cut to make them perfect. His solution just has too many fits and parts. I know mine were made well, reamed, all work done on collets, etc...but they still wobble a little.

Offline NickG

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Re: Senft "Poppin" engine
« Reply #40 on: March 15, 2018, 12:37:13 PM »
I know what you guys are saying re flywheels. On mine it was a different story. I usually struggle with flywheels but because I made the rims first then the hub, turned to a good fit for rim, drilled and reamed and thread cut all at same setting in chuck these turned out to be my best flywheels!!! Then as you did the flywheel can be mounted for a final skim.


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Offline Brian Rupnow

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Re: Senft "Poppin" engine
« Reply #41 on: March 16, 2018, 12:36:43 AM »
I can't swear to this, but my plan to address the flywheel issue is this. I will probably build the cam and cam washer and install them on one of the flywheels, then mix up a batch of J.B. Weld, coat the hubs with it, insert hubs into flywheels put cam and cam washer on one of the flywheels, then run the nuts down tight, and clean up any squeezed out mess. This should make each flywheel assembly a "composite unit". Then after 24 hours I will mount each assembly on a 3/16" arbor, tighten in place with the set-screws in the hubs, then true each flywheel individually. I am not concerned about balance here, just visual "flywheel wobble".

Offline Art K

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Re: Senft "Poppin" engine
« Reply #42 on: March 16, 2018, 02:30:40 AM »
I only have two engines that I have built. So that doesn't make me an authority on flywheels, but. I have turned all the essential stuff on the one side and then flipped it to turn the other side. My Upshur single I did the back side then flipped it and turned the front including setting the angle to bore the taper and then while that was set turning the taper lock portion. That idea straight out of the model engine maker magazine. That engine will run 7500 rpm. Quite happy with that. Although I am quite the opposite of you and am more likely to see how fast it will go rather than the opposite. :mischief: Although I did have it running 400rpm.
Art
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Offline Ian S C

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Re: Senft "Poppin" engine
« Reply #43 on: March 16, 2018, 09:08:16 AM »
An important thing with graphite pistons: there must be NO oil on it. This could with some engines be difficult if oil is thrown off the crankshaft from over lubricated  plain bearings.
Ian S C

Offline bent

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Re: Senft "Poppin" engine
« Reply #44 on: March 16, 2018, 05:48:10 PM »
ArtK,

Hmm...taperlock bushings for flywheels? Wondering how that would look on a 1/4" shaft...any pictures you could share?

 

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