4 stroke.

[Speedy]

I have always been interested in the rc line of 4 stroke engines, and recently been researching how to convert them from nitro to gas.
after roaming the usual forums a canadian member offered me his saito 80 engine pictured below for free just pay 10$ shipping.
it will arrive disassembled but thats alright with me.

I think this is a perfect opportunity for me to understand how our little engines operate and should keep me busy.
these engines have piston rings to my understanding, wont see much updates for awhile last 2 months of school... busy time.

will convert the following, or so I hope.
nitro > gas
air cooled > liquid cooled
connecting rod bushings > needle bearings
nitro carb > gas carb
I have also read about oil in the crankcase and circulating it to the rockers from a pump on the carb, hmm that needs more research.

it will be expected to loose about 20% of power that the nitro had.
when stock the rpms are around 12000.

 

[gbritnell]

In going over your list of conversions there's really only one that would change, the fuel. A nitro carb can be used for gasoline, it will just take different adjustments.
As far as the others I'm not so sure on liquid cooling, that will take a whole lot of work for no difference in performance. You could do it but it would take a circulation system with a radiator of some sort. You could put oil in the crankcase and just use it as a splash system but as far as the rockers, however they are lubricated presently would be adequate for periodic use. With a four stroke type engine the fuel/oil mixture goes directly into the cylinder and not through the crankcase so therefore the rockers must have some lubrication of their own.
gbritnell

 

[mu38&Bg#]

The spark conversion is easy. Liquid cooling can be done. I have it in mind for an OS FS-30. I wouldn't bother with needle bearings. Crankcase oil might be interesting and there are a few simple ways to accomplish it, but I haven't tried yet. The amount of oil in the fuel can be greatly reduced from what is typically used in glow fuel. I've been running 8% oil in E85 fuel in an FS-52 on spark and it's been great and runs very clean. You can see some info here. A Walbro type carb is fairly large for a Saito 80, others have run Saito spark conversion on gasoline with the stock carb, but the needles will be very touchy. You would normally keep the RPM down around 10k on an engine this size. I have a Saito 80 on the bench waiting for new bearings right now.

 

[Speedy]

humm, I was under the impression that gasoline would swell the gaskets in the carb?

the water cooling would be to use the engine on a offroad 4x4. I know people have used a fan powered by a belt off the drive shaft for air cooling with great results, but I wouldnt mind attempting the water cooling

DieselP
why wouldnt you bother with needle bearings? it seems all the conversions people did were with needle bearings.

what ideas did you have for crankcase oil?

thanks for the replys
keep them coming 8)

 

[mu38&Bg#]

humm, I was under the impression that gasoline would swell the gaskets in the carb?

Yes, so the needle is a little tighter. There are no O-rings that will change the way the carb works.

the water cooling would be to use the engine on a offroad 4x4. I know people have used a fan powered by a belt off the drive shaft for air cooling with great results, but I wouldnt mind attempting the water cooling

It will be a little tricky. I think the biggest problem is the need for a pump. I supposed a Perry Pump would be OK. I think i have a tiny Robart pump for my project. I also want to put a liquid cooled engine in a truck. I'm still trying to decide if I do that or the fan.

why wouldnt you bother with needle bearings? it seems all the conversions people did were with needle bearings.

Glow four strokes do not have needle bearings. I only know of the one thread on RCU were the guy put a needle bearing on the big end. All the others have run without needle bearings. They simply aren't needed. Oil accumulates in the crankcase of a model four stroke . This is different compared to two strokes where very little oil is present at any time.

what ideas did you have for crankcase oil?

There is a setup where you use a couple check valves and tubing to route crankcase oil (mist) to the rockers and back down to the crankcase. The fluctuating crankcase pressure does the pumping.

 

[solver]

Speedy, on what size of rc car are you going to use that engine?

If it's something like 1/8 scale, you might lower that engine's compression ratio, unless more aggressive behaviour is desired.

 

[Speedy]

thanks DieselP
lots I didnt know.

my neighbor does small engine repair hes going to see if he has a carb with a small ventury, if not the stock carb like you said will work

so is the connecting rod splash lubricate then to begin with?

my engine is shipped today, still need to find a ignition box of some sort (probably a airplane one) then the fun can start.... well... after school work.

Solver.
I have no clue how big this engine is, havnt researched much on it. I am building a 1/10th trophy truck or maybe put it in a 1/8th savage.

 

[solver]

Speedy, that saito 80 has roughly about 12 ccm displacement, so it could well provide enough power for 1/10 or 1/8 scale car, even if you drop its compression ratio, since there is no need to run that big engine at full speed to get the torque.

But take your time, when testing that engine.

Addition: Lower you tune it, less it produces excess heat. Also whole engine lasts way much longer that way.

 

[hitnmiss]

I used to fly R/C alot but haven't for some time now.

Back in the 90's I had a Saito 80 just like you've pictured. Saito's have a great rep but my Saito 80 never ran right from the start. I fancy myself an excellent glow engine tuner but I could never get that Saito to run well. It had very good power but would always seem to overheat even if I ran it blubering rich.

I tried carbs, fuel, plugs, etc. I finally gave up on it and sold it to a friend who thought he could make it work...

Later I saw that the Saito 80 has a much higher compression ratio than the other Saito engines and always wondered if that was the basic problem with mine...

Might be worth looking up the C/R and adjusting if you run into problems.

 

[Speedy]

thanks for all the advice so far

I am still looking for a ignition module, hope I dont have to spend allot on that.

should I drill and tap for a NGK cm6 plug?
I dont want to use the specialty plugs if I can get away with it. cm6 will probably be more cheap and easy to find.

 

[mu38&Bg#]

I don't think there is room for a CM-6.

 

[solver]

Speedy, one possible solution would be to convert that glow plug to spark plug. It would require some tooling, though.

That way there isn't need to re-thread an existing spark glow plug hole.

 

[mu38&Bg#]

1/4"-32 spark plugs are a little expensive at ~20USD. But compared to the number of glow plugs you'd eat they are still cheap. I have used various 1/4" plugs. The only thing really available in current production is the Rimfire. http://sparkplugs.morrisonandmarvin.com/ Older makes like NGK, Champion, and Stitt can be found on Ebay at reasonable prices sometimes.

 

[Speedy]

do you know of the NGK ME8
is still available?.

 

[mu38&Bg#]

Even though it is still listed in NGK catalogs, (I actually saw it in a current NGK catalog at Farm and Fleet), I don't think they are actually available. They list at over 20USD, so Rimfire plugs cost less at ~17USD. I picked some ME-8 up off Ebay just recently because they were very cheap. There is also a Chinese 1/4"-32 spark plug out there. Many of the people who sell the RCEXL ignition will sell this plug, but I've heard the quality is substandard. I think they usually go for 10USD or less.

 

[joe d]

Hi

Debolt machine is listing ME-8s at $25 USD each

Joe

 

[Speedy]

dieselpilot do you have a link to who makes the chinese plug RCEXL sells?

thanks Joe D.

I am also asking in with my neighbor that does small engine repair, if he can get me the NGK's I might go that route.
he usually gets plugs for very cheap, I am hoping this would also be the case. he lets me buy at cost.

does champion or any other known manufacturer sell these plugs?

thanks for the help guys!

also, I have some leads on good used ignition boxes.

 

[mu38&Bg#]

It would be interesting to see if NGK still makes them, but don't hold your hopes high. I have no idea who makes the Chinese plug and I doubt RCEXL will give up their supplier.

Have you tried these people? They have the ignition and plugs at reasonable prices. I've never bought anything from them.

http://www.prcmodel.com/modeng/name/onlinestore/category/7

 

[Speedy]

engine just arrived, but I am still at school :-\

I am debating weather I should just make a fan with a shroud that is belt/oring powered from the engine for cooling.

TCS said they have used their product to liquid cool nitro engines and it worked adequate
http://www.micropumps.co.uk/

anyone have any idea how one would go about putting a water jacket in? or ideas.

 

[kf2qd]

Biggest problem with coinverting to gasoline is contolling heat. Alchohol fuel provides quite a bit of cooling and a bit of supercharging effect that you will lose with gasoline. You may also have problems with the shape of the head.