Nemett Jaguar--Canadian style

[doubletop]

Brian

Encouraging to hear you had good results with the Nemet carb. My Bobcat build was my first ever I/C engine so I had no yardstick to measure the results. (yes truly a beginner in my case)

As for the valve problem Interesting? But all good info for the other builders. I had thought the valve spring sitting on the shoulder on the head would act to pull the valve and the valve pull the seat into the head. If its come loose either the valve too tight in the guide or more likely the loctite can't stand the heat? In one of the videos of a Nemet engine the exhaust is glowing red hot. (I can't find it at the moment). Then again maybe the Nemet carb is running lean and another source of overheating?

The thought of melted vitton rings? Isn't overheating Vitton a safety problem?

Pete

 

[Brian Rupnow]

It might be a bit tricky getting the positioning right, but a #6-32 pan head screw positioned so as to catch the edge of the valve cages but clear the head of the valves would be an easy "safety" add on. It would only require a #6-32 hole be tapped into the aluminum head. I would tap it all the way through and put a safety nut on the outside of the head to keep the screw from unthreading itself. There is sufficient head to piston clearance to clear the head of the screw with no difficulty.

 

[Brian Rupnow]

Brian

Encouraging to hear you had good results with the Nemet carb. My Bobcat build was my first ever I/C engine so I had no yardstick to measure the results. (yes truly a beginner in my case)

As for the valve problem Interesting? But all good info for the other builders. I had thought the valve spring sitting on the shoulder on the head would act to pull the valve and the valve pull the seat into the head. If its come loose either the valve too tight in the guide or more likely the loctite can't stand the heat? In one of the videos of a Nemet engine the exhaust is glowing red hot. (I can't find it at the moment). Then again maybe the Nemet carb is running lean and another source of overheating?

The thought of melted vitton rings? Isn't overheating Vitton a safety problem?

Pete

The spring doesn't set on a shoulder in the head. The spring sets on top of the valve cage. If the valve gets a bit sticky in the cage and the Loctite bond between the cage and the head isn't good, the rocker will push the valve and the cage down into the cylinder.

 

[Jasonb]

Brian what Loctite did you use as some have a higher temop range than others, Although mu cages were a nice press fit I also added a drop of 648 for good measure.

Pete, its the Lynx with the red hot exhaust not a bobcat though still pressed in.

[ame]http://www.youtube.com/watch?v=wTq0ogyTFEc[/ame]

 

[Swifty]

Wow, I hope that the exhaust on my Lynx doesn't get that hot. I see that the exhaust is made of that thin wall flexible pipe, probably more prone to getting red hot.

Paul.

 

[Brian Rupnow]

I have (hopefully) solved my valve cage issues and reassembled everything, with the Nemett style carburetor. A minimum of messing about this morning had it running as you see in the video. I'm quite happy with it, but it really must have a fan.--It gets far hotter than I am comfortable with. I want to keep playing with the timing and the carb until it ticks over at a much slower idle and runs consistently, but I think I am 99% there. I have been saving a small electric motor with a plastic bladed cooling fan on one end of the armature, and it may be exactly what I need for this.
[ame]https://www.youtube.com/watch?v=xr3Hzut5Gj0&feature=youtu.be[/ame]

 

[Brian Rupnow]

Oh Bummer!!! The fan I've been saving is too much hub and not enough blade. It's a bit too large as well. The ideal size would be 2 3/4" o.d. with a "smallish" center hub suitable for a 3/16" or 1/4" shaft. I could probably cut down the diameter of this fan to what I need, but then it would be all hub and very little blade. I have a very strong aversion to having my fingers whacked by a metal fan or propeller, so will enclose whatever fan I use with a band of aluminum incorporated into the mount and bearing. I guess I will have to go and patrol the dollar store or??? to see what I can come up with.

 

[Brian Rupnow]

Hah---Look at that cute little devil!! $8 at the computer store--the diameter is exactly what I wanted and the pitch is right to blow cool air onto the cylinder. I would have preferred some color other than white, but you work with what you can get (there is always plastic paint). I have never had one of these things apart before to know how to put a hub/shaft set up on it, but I'll know in about 10 minutes---

 

[Brian Rupnow]

After thoroughly trashing the guts out of it, I find that there is a nice concentric ring cast into the plastic in the center. The plastic fan itself has a thin metal ring which is pressed into place over some "snap-lock" thingies that are cast into the inner diameter of the plastic fan itself. Since this fan will not be turning at warp speed, I'm not horribly concerned about balance, so a round piece of aluminum or brass or even possibly steel with a hole for the shaft in the center can be Loctited to the inside of that thin steel ring. I have to do some thinking on this, and since I have an abundance of 10mm ball bearings I may incorporate one into the hub. If I do this right and put an o-ring groove in the outside of an extended hub with the bearing in it, then I don't need a live shaft at all.

 

[gus]

Carbs,

I have one OS Carb bought for the Rupnow H&M Engine which did perform well and about to buy another OS Carb good for Nemett-Lynx Engine. Also plan to make the Nemett-Lynx Carb too. It is a hard fact that carbs must match to give good throttling range.

Been watching Nemett-Lynx Engine Videos. Meanwhile the finishing line is a mile away for Gus. I have to cook up some tooling to cut the cams. Will be tapping Brian's and Paul's brains for expertise.Taking my sweet time to finish up.

Good News. The valve guides were a bit tight press-fitted in. Made and throw away 4 pieces as the fit was either sloppy or only tight push fit. Will cut new valves and lap today. The valve springs using the prescribed SWG 20 seems a bit too strong. Will try out softer
springs.

 

[doubletop]

Pete, its the Lynx with the red hot exhaust not a bobcat though still pressed in.

I had thought it was but it still indicates the sort of temp the exhaust of these things get too. 300deg C won't cause a red hot exhaust but it will undo locktite.

I had to go back to the drawing to prove myself wrong. On my lynx I didn't like the valves seating on the ally so did a hybrid

You'll see the springs sit on the original ally shoulder. However the bobcat/jaguar valve guide/ seats don't have that shoulder in the head

Pete

 

[Swifty]

The video of the Lynx with the hot exhaust appears to have a water cooled jacket and flywheel. If it had a propellor it would be cooled by the back draught.

Pete, I went and looked again at your video of the engine running, the propeller seems to be a good size for the engine, what size is it? I will only be using a prop for display on my bookshelf, so will start looking for a cheap one.

Paul.

 

[Brian Rupnow]

It wasn't a big deal to suss out a design for my fan, and no big deal to build it. The only thing I don't really like is that the fan ends up being almost as big as the engine.

 

[gus]

I had thought it was but it still indicates the sort of temp the exhaust of these things get too. 300deg C won't cause a red hot exhaust but it will undo locktite.

I had to go back to the drawing to prove myself wrong. On my lynx I didn't like the valves seating on the ally so did a hybrid

You'll see the springs sit on the original ally shoulder. However the bobcat/jaguar valve guide/ seats don't have that shoulder in the head

Pete

I sort of trust Malcom's valve seat design and now I have some doubts. May have to put in valve inserts too. Please post same drawing. However will spin/run engine before put in the valve seat inserts.

 

[doubletop]

Paul

The prop is a Master Airscrew S2 Series 16x6 part # MA1660S from HobbyKing

Gus

No drawings I just winged it with some notepad sketches. The Bobcat came after the Lynx so I guessed Malcolm had realised that bronze seats were needed. Get the Bobcat drawing to see what is required and make the internal sizes to the Lynx dimensions and the the external dimension about 1.5mm larger. There is plenty of meat on the Lynx head to accommodate these. Insert the cam seats before you drill the ports in them. You'll notice that I've also put bronze sleeves in for the cam followers.

Brian

Apologies fro hi-jacking your thread

Pete

 

[doubletop]

It wasn't a big deal to suss out a design for my fan, and no big deal to build it. The only thing I don't really like is that the fan ends up being almost as big as the engine.

Brian

It occurs to me you could have made the water cooled jacket by now, and people would still be able to see the engine

I did see somewhere a magnetically coupled water pump, no need to worry about sealing the drive shaft. I just couple my water jacket up to the water tap and trickle water through the jacket.

Pete

 

[doubletop]

Just found this

http://www.hobbyking.com/hobbyking/store/__11601__Water_Pump_for_Gas_Engine_Boats.html?strSearch=water%20pump

Hide it in a brass tank?

Pete

 

[Brian Rupnow]

I'm not sure just what to do. The engine is running good as it is. Any fans I have designed look so big and clunky that they overwhelm what is really a pretty little engine. As long as I don't run the engine for more than 10 minutes at a time, I probably don't have to do anything. What do the Bobcat and Lynx guys do with their air cooled engines without propellors? How long do they run at one time.---Brian

 

[GailInNM]

Brian,
In the "For What it Worth" department: When I built my first "Tiny" using a Viton piston ring it ran very hot. After changing to a lapped cast iron piston in a CI cylinder the temperature dropped considerably. I made temperature measurements at the time, but did not record them but as I recall it was about 50 degrees F. This was running about 6000 RPM. I converted to hit and miss shortly afterwards so did not do any further checking.

I don't know, but you might see similar results if you go to the cast iron rings as you have indicated that you might do in the future.
Gail in NM

 

[Brian Rupnow]

For what it's worth--I learned two things today. Firstly, the Jaguar carburetor will work well with the throttle spool vertically aligned, as you see it in the last video I posted. But--The caveat is that when its set up like that, the needle valve ends up on the bottom of the carb, and is consequently lower than the gas tank--and it will slowly drip-drip-drip around the needle valve threads until the gas tank is empty after you have shut down and walked away from the engine. Second thing I learned, is that when you turn it so the throttle spool is horizontally aligned, (the way Malcolm intended it, I believe), and the exhaust system is set up like mine, you can burn the Hell out of your thumb when trying to blip the throttle handle!!!.----Tomorrow I will build a longer throttle handle. As far as a cooling fan goes, I am still undecided. Since it is Canada day here, all of the stores are closed, so I haven't been able to do any searching for a 2" diameter fan blade with a small hub.