My Improved Snow Engine

[Rustkolector]

This is the proverbial Snow tandem double acting gas engine designed by Doug Kelley that I built in 2008. It is my favorite model engine. I never took any video of it at the time. Over the years this little engine and I have had our ups and downs and finally last year we had a bit of an accident, I admit, it was my fault. So over the last year I rebuilt this Snow and was determined to incorporate what I think are some needed changes to address the issues I was having with my Snow engine. In particular, my Snow would not continue to run without running at a very high rate of speed making everything moving on the engine a complete blur. Other Snow owners might be familiar with these issues.

So far, it seems to be running well and it will now continue running through a tank full of fuel. The engine is running at 350 RPM in the video.

Jeff

 

[kuhncw]

Jeff,
Your Snow looks good and it's running very well.

Chuck

 

[oldengineguy]

Jeff: Good running engine! I just completed a Snow (July 14) and have tried to start it only once, it popped and the cylinders got warm but it would not sustain itself. Work and other things have not allowed time to get back at it. One of the things I see different about your engine is the inlet manifold. Is it water heated? Did you run the water outlets into one then along side the inlet then back to the tank/ rad.? Did you redesign cam profiles? No secrets , PLEASE tell all. Thanks Colin P. S. Once I figure out how to post pictures, I'll have a go at that .

 

[Rustkolector]

Colin,
With a new untried engine you have to know for sure that you have good sealing piston rings and valves. An absolute must on the Snow. Your pistons should not contact the cylinder walls. The pistons should float between the two piston rod bushings on each cylinder head. If all is good, you should feel noticeable compression on all 4 cylinders. Like most Snow builders, you are likely to have piston rod set screw retention problems with the coupling and maybe the pistons. I pinned the pistons and used a positive clamping split coupling on the piston rods. I allowed no clearance between the two mating piston rod ends at the coupling.

One of the two most significant changes I made was to change the intake manifold to a flat plane log type manifold for simplification and to heat it with jacket water. I circulate all coolant through the manifold and back to the coolant reservior. There is considerable heat lost to fuel vaporization as you probably have experienced. Use a tiny carburetor. Even if the engine runs with the original intake manifold, it will run with a wet sloppy exhaust and it will only run at relatively high speed.

The second significant change is the cam lobe profile. The original Snow engines have odd valve timing and were known for poor running at light and no load conditions. Two valves, one cam, what else would you expect? They just don't breathe well. The new cam alone has gotten two other Snow engines running that previously would not run. I detailed the cam lobe change in a past post on this same subject. I suggest you read the whole thread to see what problems others have run into. Snow engine thoughts

Jeff

 

[oldengineguy]

Thanks Jeff: Yes, I think my pistons are too tight. I will definitely change the manifolds . Cam lobes are50 degree ( I wanted to try a compromise) Back to the shop! Colin

 

[oldengineguy]

Colin,
With a new untried engine you have to know for sure that you have good sealing piston rings and valves. An absolute must on the Snow. Your pistons should not contact the cylinder walls. The pistons should float between the two piston rod bushings on each cylinder head. If all is good, you should feel noticeable compression on all 4 cylinders. Like most Snow builders, you are likely to have piston rod set screw retention problems with the coupling and maybe the pistons. I pinned the pistons and used a positive clamping split coupling on the piston rods. I allowed no clearance between the two mating piston rod ends at the coupling.

One of the two most significant changes I made was to change the intake manifold to a flat plane log type manifold for simplification and to heat it with jacket water. I circulate all coolant through the manifold and back to the coolant reservior. There is considerable heat lost to fuel vaporization as you probably have experienced. Use a tiny carburetor. Even if the engine runs with the original intake manifold, it will run with a wet sloppy exhaust and it will only run at relatively high speed.

The second significant change is the cam lobe profile. The original Snow engines have odd valve timing and were known for poor running at light and no load conditions. Two valves, one cam, what else would you expect? They just don't breathe well. The new cam alone has gotten two other Snow engines running that previously would not run. I detailed the cam lobe change in a past post on this same subject. I suggest you read the whole thread to see what problems others have run into. Snow engine thoughts

Jeff

On Aug 23 I managed to get my Snow engine to run. After the first attempt on July 14 I took Jeff's suggestion and made a different piston rod coupling and made sure that pistons were not contacting cylinder walls. I reset the cams using low pressure air applied to the sparkplug hole to listen for valve open and close. Have not made a new manifold yet, but proved ( by using a heat gun) that is a needed improvement . Engine does not have a proper cooling system yet, I was using a total loss system from an upper tank with a valve to control flow trough the engine to a catch bucket on the floor. Very satisfying when it finally makes the right noises . Colin

 

[Rustkolector]

Colin,
You have been busy. Glad you are getting positive results.
Jeff

 

[a41capt]

On Aug 23 I managed to get my Snow engine to run. After the first attempt on July 14 I took Jeff's suggestion and made a different piston rod coupling and made sure that pistons were not contacting cylinder walls. I reset the cams using low pressure air applied to the sparkplug hole to listen for valve open and close. Have not made a new manifold yet, but proved ( by using a heat gun) that is a needed improvement . Engine does not have a proper cooling system yet, I was using a total loss system from an upper tank with a valve to control flow trough the engine to a catch bucket on the floor. Very satisfying when it finally makes the right noises . Colin

Interesting troubleshooting. Looking forward to seeing your video of a successful run Colin!
John

 

[oldengineguy]

The Snow runs! On aug 28 managed to get engine to run as slow as 600 rpm for about 10 mins using naptha gas & 2stroke oil. Did not have heated manifold but ran O.K. once warm. Had to shut down due to knocking sound .My split clamp for piston rod did not work. Also #3 cyl piston rod bushing in cyl head had come loose. Easy fix on the bush I'll make another with slightly larger o.d. for a tighter press fit. Jeff, could you post a drawing of your clamp design? Also, what do you liquid cooled guys use for a radiator? I'm sure this is going to be a "runner" Thanks Colin

 

[Rustkolector]

Colin,

Glad to hear you continue making progress. I used a piston rod connector that another Snow builder designed which takes careful close tolerance machining of the coupling and the rod ends. I machined the coupling completely in one piece before cutting it in two with a .010” slitting blade. The two piston rods should butt against each other snuggly when assembled. See sketch. If you are going to make new piston rods, I would recommend using stainless steel rod meeting (TG&P turned, ground, and polished specs). My Snow had considerable hours on it before I rebuilt it. Both of my piston rods made of O1 drill rod had considerable corrosion and pitting. A temporary close fitting .312” dia. delrin filler sleeve that is slit and snaps over the shaft end relief allows the piston rods to be inserted without damage to the seals.

I used a simple pumped reservoir (tank) cooling system for my Snow, a bit larger, but similar to the original drawings. As such, the original engine heat was radiated to the air from the engine heads, cylinders, coolant piping, and all other surfaces of the pump and tank cooling system. It wasn’t meant for running much longer than 10 minutes at a time. However, if a relatively efficient coolant jacketed intake manifold is installed it will provide additional cooling capacity and should allow running for periods of about 20 minutes before reaching 150F. If the engine is run slow, running time will increase. A radiator and fan should not be needed.

Jeff

 

[oldengineguy]

Jeff
Thanks for the info. Back to the shop after purchase of a smaller boring bar insert. Colin