Ohh I’m kind of exited Japanese 2 stroke??

[Thepaetsguy]

The new engine/transmission mount is complete and the engine and transmission is bolted to it.

Ready to set down and be welded to the bars of basically any mini bike I can get my hands on. I’m not against building another one myself.


I intend to buy a fully adjustable tec carburetor from an H40 now that I know it can be modified to fit. The one on there now has zero adjustment at all.

 

[Thepaetsguy]

Ok so I am still unsure of how the oiling system works. It has the oil dropper cap on one side and a funnel looking thing on the other side of the block with a spring loaded block drain cap.

If I’m supposed to be thinning motor oil with fuel and pouring it in the cap AND down the funnel to oil the crank and I haven’t been doing that then I’ve been running it basically dry this whole time?


I think todays job is to start by pulling the simple carb/exhaust that is on there and unbolting the head. I can lift the jug back off the piston and look down into the crankcase like I should have the first time.

I got this engine running and now I’m terrified to run it. If I make sure I’m using the oil system correctly I’ll feel a lot better.

 

[Thepaetsguy]

I have to look back through but whoever said it was a funnel for crankcase oiling was correct! It’s a funnel to a small hole that exits right above the crank weights!

The oiler on the other side is self explanatory. Thank you all I feel more comfortable thinning out some motor oil for the crankcase when I run this engine.

The rings piston and bore look great! I have it re-assembled and know am more confident going forward running it.

 

[Thepaetsguy]

Ok update this funnel was stuck! It took some tapping and persuading but it finally popped loose and pivots.

There is no off/on position for the funnel. You could pour thinned down oil right into the crankcase while the engine is running? does the piston port mean it can run fine with the crankcase venting through the funnel while running?

The bottom of the case is round and so it the rod cap. The rod cap and bolts are very very close to the bottom of the case. Should I be treating this engine as sort of a four stroke where they expect some oil in the bottom case to sling around as the rod cap hits it? It would sling it right up the side of the round case.

 

[sparkwizard]

If the crank case is open to the carb with the piston at TDC, it will not run well with the oil funnel open to atmosphere.The lower case is the pump that fills the cylinder with fresh charge. Did you get any pictures with the jug removed?
That is a two stroke engine. It might have collected some lube down there since it probably used 30wt at about 16:1. I SUSPECT that funnel was for FLUSHING the oil out between run. I seem to remember seeing a drain plug at the bottom, right?

 

[Thepaetsguy]

If the crank case is open to the carb with the piston at TDC, it will not run well with the oil funnel open to atmosphere.The lower case is the pump that fills the cylinder with fresh charge. Did you get any pictures with the jug removed?
That is a two stroke engine. It might have collected some lube down there since it probably used 30wt at about 16:1. I SUSPECT that funnel was for FLUSHING the oil out between run. I seem to remember seeing a drain plug at the bottom, right?

The only way to drain the block I see is a spring loaded cap at the very bottom of the block.

The funnel is above the crank weights and is absolutely for pouring oil that would drip off the weights into the bottom of the round crankcase.

I do not know if there is a seal that is bad and the funnel is supposed to be pushed down when running and pulled up to add oil before starting? But there is no position that ”shuts“ the funnel off so it wouldn’t be a massive crankcase leak.

I’ll get pictures later as I can very very easily pull it back down.

 

[Mr. Pink]

If I’m supposed to be thinning motor oil with fuel and pouring it in the cap AND down the funnel to oil the crank and I haven’t been doing that then I’ve been running it basically dry this whole time?

I remember learning about cold weather oil dilution on WWII aircraft during my A & P training.
Here is what Google has to say on the subject:


During World War II, oil dilution was an essential procedure used by Allied and Axis ground crews to prevent thick engine oil from freezing in extreme cold weather.
The process and mechanics involved the following key elements:

• Before Shutdown: Just before shutting down an engine after a flight, the pilot or flight engineer would engage an oil dilution switch or valve.
• Injecting Fuel: This action opened a solenoid valve, allowing a measured amount of aviation gasoline (avgas) to be injected directly into the engine's oil system.
• Mixing: The engine was allowed to idle for a few minutes to ensure the fuel and oil were thoroughly mixed.
• The Result: The gasoline lowered the viscosity of the heavy engine oil, keeping it fluid enough to prevent the engine from seizing in freezing temperatures.

• No Multi-grade Oils: Because modern multi-grade (e.g., ) oils did not exist yet, wartime mechanics relied on single-grade, high-viscosity oils (like -weight). In sub-zero temperatures, this oil would become thick like molasses, making the propeller nearly impossible to crank.
• The 'Boil-Off': When the plane was needed for the next flight, the diluted oil allowed the engine to start easily. As the engine warmed up during the subsequent flight, the highly volatile gasoline quickly evaporated (or "boiled off") through the crankcase breather, returning the oil to its normal, protective viscosity.

• Over-dilution: Determining the exact amount of gasoline was a guessing game. If too much fuel was added, the oil became too thin to withstand combustion pressures. This caused "blow-by," forcing an oil/air mixture out through the crankcase vents and often spraying the aircraft's windshield.
• Under-dilution: If not enough fuel was injected, the oil would remain too thick, leading to high friction, starter motor failure, or an inability to turn over the engine at all.
• Safe Ratios: Mechanics generally targeted a dilution of roughly to fuel-to-oil, depending on the anticipated overnight temperature lows.

 

[sparkwizard]

Take that knurled nut and spring off the trumpet pivot point and pull the trumpet out. I think it is the valve. When pivoted up, the valve opens, pivoted down, it seals the case.

 

[Thepaetsguy]

Two flywheel ”marks” 180 degrees apart.

With the piston at the very bottom of the cylinder the flywheel matches up directly to the flywheel mark with the “T”


With the piston at TDC the flywheel mark without the t lines up directly? So the factory marked the “T” on the wrong side of the flywheel??? Small note.

 

[Thepaetsguy]

Fuel exits the carburetor and hits the intake port. Goes through the intake port and enters the bottom of the cylinder while the piston is at TDC.. Fuel travels through the cylinder then through pistons port into two ports along the side of the head that dumps it into the cylinder above the piston.

I don’t think much fuel is scavenged in this process to oil the crankcase as the jug is slip fit into the engine case with a gasket.


I understand fuel will get through to the crank when it’s on it’s way through the pistons ports but there is a long path fuel has to travel to get to the cylinder to explode I’m baffled is it still done this way today?

 

[RobertC]

Take that knurled nut and spring off the trumpet pivot point and pull the trumpet out. I think it is the valve. When pivoted up, the valve opens, pivoted down, it seals the case.

Dang Dave @sparkwizard , and @Thepaetsguy , the amount of shared knowledge here still blows me away.

 

[sparkwizard]

Yes, Sir, modern 2 stroke engines operate just like that. Some have reed valves into the lower case but they all still lubricate the lower end and the piston and rings just by the oily mixture in the fuel.

 

[Thepaetsguy]

I was wrong pushing the funnel to the down position and locking the twist ring does in fact completely close off the passage.

I will pour a hefty amount of some thinned down oil in the funnel let it drain into the crankcase and then turn the funnel “off”. Add a good bit to the dropper for the other side of the crankshaft. And mix the fuel heavy when I run this engine.

Maybe they thought this wasn’t needed? The later engines from 44/45 didn’t have this setup at all.

The internal machining on this most likely hasn’t been seen since the guy who assembled it in 1941…

 

[sparkwizard]

That looks like what I suspected. Maybe prelube the crank, or flush the case, but it has to seal the case before it will run. This a really interesting, old engine.

 

[Havasu Dave]

Piston port technology is now relegated to weedwackers and RC engines. They went to reed induction in the 70's on almost all motorsports two stroke products. The reason they are able to stay lubricated in this total loss system is that the oil is constantly being replaced in the crankcase with new oil. The amount of oil is so prolific that many of these engines have drains to they don't over pressurize the case with unburnt oil. Another aspect of modern technology is that what used to be a 20:1 mix ratio in the 70's can now be accomplished with a 50:1 because the oil is that much better. The eliminates what used to be a problem with excess oil in the case. Old technology. Old news. Now almost extinct.

 

[Havasu Dave]

Hey Partsguy, I pressure check my cases to 8 PSI and ensure it holds for a few minutes. Leaky cases will support combustion up to a point, but the more sealed they are, the better they run. A leaky case will be hard to start, and not produce optimum power. I made a test fixture with a shraeder valve and various rubber stoppers, and gasketed bits of metal. I pressurize from the intake side, and block the exhaust with a stopper using a hand pump built for the purpose. An air compressor with a very low setting will work as well but you can blow seals off the crank if you over do it.

 

[Thepaetsguy]

I have ordered an H40 carburetor to swap onto it and have a much better idea of how I should be running it. I’ll just see how it runs. Most of the carburetors I have tried on it so far worked enough but were just not even close to being right.

I still fear damaging it by running it. I’ve told this story here before the great stonebro fair a guy was reluctant to run a vintage tractor he was displaying. They convinced him to start it and the rod busted right through the side of the block. He displayed it non running for years after.

 

[sparkwizard]

On my old smokers, I am very carteful to run the mixture fresh, well stirred and RICH! 30 wt non detergent engine {lubricating) oil and I mix it at 1.5 CUPS per gallon in a 2 gallon can. If you add that much oil to a one gallon can, you can't get a whole gallon of gas in there with it.
I define older smokers and bushing engines like yours. Full bearing engines are a different breed, but thick slimy gas is what you want to run in this rare gem. Some of it might not burn, as mentioned above, and fall out of suspension and stay in the bottom end. It would seem like the engine would be gutless with that much oil, but they seem to like it just fine. That is about 10.5:1. 12:1 is what some of my oldest ones used, so 10.5 is a safe bet. Use NGK plugs if you can find them.

 

[Thepaetsguy]

On my old smokers, I am very carteful to run the mixture fresh, well stirred and RICH! 30 wt non detergent engine {lubricating) oil and I mix it at 1.5 CUPS per gallon in a 2 gallon can. If you add that much oil to a one gallon can, you can't get a whole gallon of gas in there with it.
I define older smokers and bushing engines like yours. Full bearing engines are a different breed, but thick slimy gas is what you want to run in this rare gem. Some of it might not burn, as mentioned above, and fall out of suspension and stay in the bottom end. It would seem like the engine would be gutless with that much oil, but they seem to like it just fine. That is about 10.5:1. 12:1 is what some of my oldest ones used, so 10.5 is a safe bet. Use NGK plugs if you can find them.

My local Napa and many many stores I looked for any spark plug that would work. It was a small vintage style shop in the next town over I stumbled upon that only had a few plugs in stock. All ngk and compared to the plug in it the guy said this was the closest heat range.

Ctu’s pop up on marketplace but are never cheap. We are talking add taxes to the price and you could go buy a new in box one.

That’s at least the type of mini bike frame I would like to stick this engine on.

 

[Thepaetsguy]

I have completely moved on from AI and google images (In American)

I have two pages open. Google translate and google images. I have tried translating keywords (tohatsu) (Ww2 two cycle) etc into Japanese and then adding those translations into google images with a picture of the engine/gearbox for the AI to use.

This gives only Japanese search results but it’s kind of frustrating as even with key words translated to Japanese (100cc two cycle WW2) (Farm equipment 1941) Etc constantly pull up results of motorcycles or motorbikes from much earlier (1920’s). One result peaked my interest and I’m now re-looking into Japanese tank “pup“ motors.