Author Topic: 25 hp fairbanks gas engine  (Read 3964 times)

chuck foster

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25 hp fairbanks gas engine
« on: November 20, 2017, 03:32:17 AM »
I have not worked on a model for just over 4 years so this weekend i figured i better get doing something .
So i decided to rebuild this engine that i originally built 10 or 15 years ago .
It is a model of a 25 hp gas engine and i think a guy by the name of tom stuart produced this kit.
The engine has run for many years but when i took a good look at it i soon found out i did not do a very good job so i hope to fix all the problems.
I will list some of the problem that i found , compression ratio was way too high and the engine would jump every time it fired. To fix that problem i chopped about .100 " off the top of the piston .
I then shortened the stroke by making a new crankshaft and i think the compression ratio is now 4 to 1 instead of 7 to 1 .
We will see if that works as it might be too low to run well .
The timing gears didnt lighn up with each other and the main bearings are worn out .
So over the next few months i hope to rebuild this engine and if you guys like i will take you allong for the ride .

Thanks
              Chuck

Offline Ian S C

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Re: 25 hp fairbanks gas engine
« Reply #1 on: November 20, 2017, 09:07:49 AM »
Chuck, I'll be following along, this sounds interesting.
Ian S C

chuck foster

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Re: 25 hp fairbanks gas engine
« Reply #2 on: November 21, 2017, 01:03:28 AM »
hi guys  :D
i think i just figured out how to resize my photos and post them so lets see how this goes  :o
these pictures show the engine as of the past weekend i will go into more details a little later .
there are several things that i did on this engine that make me wonder what the heck i was thinking when i built it. now having said that , this engine has run at shows for many years but it was just never right.
so as of last week i thought it is going to be the first victim in my new shop , so we will see if i make it better or not  :o

chuck
« Last Edit: November 21, 2017, 01:09:32 AM by chuck foster »

Offline b.lindsey

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Re: 25 hp fairbanks gas engine
« Reply #3 on: November 21, 2017, 01:12:48 AM »
You have the picture thing under control now Chuck. You could actually go up a size too 600x480 and still have small file sizes with slightly larger pictures. Nice looking engine too. Should be fun to follow along.

Bill

chuck foster

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Re: 25 hp fairbanks gas engine
« Reply #4 on: November 21, 2017, 01:18:17 AM »
i just reset the file size so the next pictures should be a little bigger ...... thanks bill


chuck

Offline kuhncw

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Re: 25 hp fairbanks gas engine
« Reply #5 on: November 21, 2017, 01:29:51 AM »
Chuck,

I'm looking forward to your Fairbanks N thread.  I have a set of these castings laying around.

If making the parts to print gives a 7:1 compression ratio, that is good to know beforehand.

Regards,


Chuck

chuck foster

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Re: 25 hp fairbanks gas engine
« Reply #6 on: November 21, 2017, 11:05:14 AM »
good morning folks

chuck : when i first built this engine the drawings were way off cause if you followed them exactly the compression ratio was out of this world. when the piston was at t.d.c there was .090" clearance between it and the cylinder head  :o  ( just a tad tight ) so check your drawings before you build .

the first two pictures are of the cylinder head and the small 3/16" hole just above the intake valve is were the fuel mixture travels to meet the spark from the ignitor. i always thought that the hole was too small so i opened it up to 3/8" . the hope is that this will let the fuel mixture into the ignitor area much easier and the engine should run better.
the third picture shows the ignitor hole on the outside of the cylinder head and i think it is 7/16"

the last picture is of the ignitor itself and please excuse the bad picture but my cell phone does not take the best pictures . in the future i will be using my proper camera instead of my phone . the ignitor is another bag of tricks that needs addressed and it will be in due time .

thanks for reading my ramblings  :)

chuck

Offline DD805

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Re: 25 hp fairbanks gas engine
« Reply #7 on: November 21, 2017, 06:15:50 PM »
Chuck,
Yes, that engine kit was from Tom Stuart who is a good friend  of mine. He sold that engine all over the world. He talked me into building one as my first gas engine project. That was one heck of an experience. Turning those large 10 inch flywheels on a 10 inch lathe was scary but I got it done. I only had to get help from Tom a couple of times. I built mine at about the same time you built yours. It has been a great running engine and I have never had to work on it at all until this year. It quit on me at the Great Oregon Steam Up and I have not got around to finding out why. Anyway I will be following your rebuild with interest.

Karl


chuck foster

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Re: 25 hp fairbanks gas engine
« Reply #8 on: November 22, 2017, 02:43:18 AM »
hi karl

i was told that some of the first engine kits that tom produce came with a cast iron base , is yours iron or aluminum like mine? i think the iron base would weigh the engine down and it would sit still and not jump like the aluminum based engines do .
when i turned the flywheels for my engine i was able to use the big lathe at work ( it will swing 30" ) so it was no problem for me .

i should mention that my shop is about an hour away at a friends house so i only get time to work on my models on the weekend . bit of a pain but while i am there i can drive another five minutes and look at vintage airplanes like these :)

chuck

Offline DD805

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Re: 25 hp fairbanks gas engine
« Reply #9 on: November 26, 2017, 09:32:26 PM »
Chuck,
Yes, Tom Told me that some of the original engines had cast iron bodies. By the time I got mine the bodies were aluminum. I have lifted Toms engine a few times and wow is it heavy. I have seen his running many times and I never noticed it jumping. Mine will bounce some depending on what kind of surface it is on. On my bench it is stable but on some kinds of tables used at shows it does jump a little but not enough to bother me. I personally prefer the aluminum body.

The ignitor is a neat device and has an interesting story. Because it is fairly difficult to make and Tom got so many calls about it, he made one that worked and started sending it out to builders upon request so they could see how it was built. For many years he sent it out all over the world and always got it back with thank you notes. Unfortunately not too long ago it didn't return and he didn't make another. I don't think this engine is available any longer. Several reasons but a primary one is that all of the smaller cast iron foundries in Western Oregon have shut down and he cant find a reliable source for the flywheels.

Karl

chuck foster

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Re: 25 hp fairbanks gas engine
« Reply #10 on: November 29, 2017, 11:49:39 PM »
well i managed to get a little bit done on the week end  :insane:

the first picture is of the rocker arm that i made all those years ago , it worked but it was ugly  :facepalm:

so i set out to make a new one and i think it turned out a bit better ( second photo )

some were along the line i have lost the drawings for this engine so now i have some photo's of the original full size engine to reference . i just hope i can make the engine better .

the one good thing about this engine is the cylinder bore is perfect , there is no wear and if i remember right it was straight honed and the end gap on the rings is still  right around 2 thou. so all is good  8)

chuck

chuck foster

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Re: 25 hp fairbanks gas engine
« Reply #11 on: December 28, 2017, 03:21:48 AM »
well now that christmas is over i can get back to working on my fairbanks 8)
like i said before i made some questionable pieces and some stuff just didnt look like a full size fairbanks model n , so i hope to correct that with this rebuild.
the first picture shows the business side of the engine. the cam follower was kind of heavy looking so i made it like the full size engine. for some reason i made the cam roller .112" below the center line of the crankshaft . dont ask me why but i did  :shrug:
so after making a new one i also made a new push rod.
the second picture shows the new cam follower on the engine but not finished.
the second picture shows milling some details into the cam follower arm.
i then had to make a new govenor lock off catch plate. i made it from a piece of bar stock and i turned one end down to .125" and that will be the cam roller pin.
then i had to attach the catch plate to the cam follower arm. to do that i had to drill and tape two 0-80 bolt holes. to hold the tap straight i got to use my tapping guide that mr marv klots showed me how to make ( thanks marv )
the last picture shows the whole bag of tricks on the engine.
i hope all this work is worth it but if not i am having fun.

in closing i have to say that there is nothing wrong with tom stuarts castings or drawings. i built this engine many years ago and now i would like to fix MY mistakes and take the engine details to the next level  :)

thanks for looking in and reading my ramblings ......... chuck

Offline Myrickman

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Re: 25 hp fairbanks gas engine
« Reply #12 on: December 29, 2017, 01:19:39 PM »
Nice to see you giving the old girl a makeover Chuck. I worked on the ignitor on one of these for a friend a few years ago and it was tricky... I've found most of these engines will work fine at compression ratios of 3-4:1 just fine. Throttling the intake will also reduce charge volume so in effect, lower compression also.
Will be checking on this one as your rebuild progresses.   Paul

Offline b.lindsey

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Re: 25 hp fairbanks gas engine
« Reply #13 on: December 29, 2017, 02:03:31 PM »
Thanks for the update Chuck. Looks like the makeover is coming along very well.

Bill

chuck foster

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Re: 25 hp fairbanks gas engine
« Reply #14 on: January 28, 2018, 11:49:12 PM »
it has been a while since i last posted as i am so busy with work and just life in general , but i have got some work done.

i have reshaped some of the main base casting to match the main bearing caps that i have made for the engine.
the governor linkage has been remade and test fitted and once i try running the engine i will be able to do the finale fitting.
the next thing to do is remake all of the ignitor trip parts and then i just might be able to run it.
i then plan on making a screen cooling system as the old thermo-syphon system is ok but i thing the screen cooler will look much better.

i hope to get some more work done this coming weekend but who knows if i will have time  ::)

thanks for letting me slowly drag this project allong  :cheers:

chuck

 

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