Howell v-2

[Gordon]

I am getting to the end of my build of the Howell v twin. I am having a problem with compression. I have plenty of compression when I take the head off and put my hand over the open cylinder. I have made a gasket between the head and the cylinder in spite of the fact that Jerry Howell said that it was not necessary. When I put the head on and turn it over I get a lot of pressure and/or suction at the ports without the valves being open. This is even when turning it over slowly by hand. I have lapped the valves using compound down to 400 grit but I still get the poor seal. Since the valves are in a separate cage loctited into the head I even put shellac around the edge of the cage to see if it was possibly leaking between the cage and the head. Still not working. The valves seem to be sealing when I suck or blow through the ports with my lungs. I am running out of ideas.

Some folks have mentioned a tool made by George Brittnell (sp?). Any link to that?

I am still confused as to how the carburetor and the crankcase vent work together but that is a problem for once I get the compression solved.

Gordon

 

[10K Pete]

400 is way too coarse. Use some 800 then finish with something finer like 1200. As to other things.....?

Pete

 

[Brian Rupnow]

Gordon--I had to do a lot of hunting to find this, but if you look at posts #257 and #260 in this built thread, you will see one of the famous George Britnell valve seat cutting tools. I made this one for the Atkinson engine I built years ago, and built a second one for all the rest of my engines which have 1/8" diameter valve stems and 5/16" diameter valve heads. The results with valve seats when using a tool like this are nothing short of amazing. I never did really figure out a good way (short of hand filing) to put a back relief on the cutting edges, but the tool seems to work perfectly well cutting brass valve seats without any back relief. I do not cut my valve seats in the lathe. I finish everything else on the brass valve cages, (concentricity really, really counts, so drill/ream the valve stem hole and the clearance above it all in one set-up). then I Loctite the valve cage into place, and then I slide the small diameter of the tool down into the valve stem hole and when the cutting edges of the tool touch the area in the valve cage which is to be cut, I turn it two or 3 full revolutions by hand using only medium pressure. the valve seat should only be about .015" x 45 degrees. NOT MORE. I machine my valves to have a 92 degree included angle, and lap them into the newly cut seats using first 400 grit, then 600 grit carborundum paste. Lap them by hand, and for gosh sakes don't lap them too much.---Brian
http://www.homemodelenginemachinist.com/showthread.php?t=18313&highlight=britnell+tool&page=26

 

[Gordon]

Thanks. I have made counterbores that way in the past. I will try it for valve seats. I think that at this point I should try remaking the valve cages. My problem is probably concentricity. As with all of these projects one small thing not being quite right causes the problem and once that is corrected it suddenly runs. Frequently I end up not really being sure what the problem actually was because I end up changing more than one thing while I am disassembling and reassembling.

 

[Gordon]

Reworked the valves and added a head gasket. Still not enough suction to vaporize the fuel properly. Wondering about remaking the piston to reduce the volume at TDC or else remake the crankshaft to increase the stroke. Not sure if that is going to solve the problem and not sure how much should be added to stroke or piston to increase the compression area. I am hesitant to try things because many other have made this engine per prints and got it running. Interesting because Gus is at the same point and having the same problems. Open to ideas.

 

[Brian Rupnow]

Gordon--I'm not really familiar with this engine you are building. The engines I build generally have a theoretical compression ratio of between 5:1 and 6:1. This number is the ratio of volume in the cylinder and the cylinder head when the piston is at bottom dead center as opposed to the same volume when the piston is at top dead center. This gives a very noticeable compression when turning the engine over by hand---IF--the valves are sealing. Remember--the seat which you cut into the valve cages should only be about .015" not more. if you have cut the seats greater than that, then chances are that more lapping is not going to remedy your situation. I make my valve cages from brass and my valves from cold rolled steel. If you can get the engine firing at all, the force created by combustion will actually "swage" the shape of the valve face into the seat, and result in an air tight seal. If you are certain of the valve timing and ignition timing, a last result is to use aerosol "quick start" ether for starting engines in sub zero temperatures sprayed directly into the carburetor while turning the engine over at about 300 to 400 rpm. to see if you can get it to start firing. Just use it with caution. Only a little bit. It is very flameable and volatile. If you are in North America, send me your phone number [email protected] and I will phone and talk about what might possibly be wrong. If you haven't seen it already, have a read through this. http://www.homemodelenginemachinist.com/showthread.php?t=25715

 

[Gordon]

This has a theoretical compression ratio of 5:1. The valves seem to be sealing well and I am not getting a good bounce back even when I plug the intake and exhaust ports. It kind of fires but just does not really run. I have been avoiding remaking the valve seats because the originals are in with loctite but that may be the next step. I can get it to fire a time or two with starting fluid but only for a couple of pops. The valves certainly seal as well as the other engines which I have built. Off to an old engine show tomorrow so I will just forget it for at least a day.

 

[Gordon]

I have been having a problem with the compression/intake. I have that much improved but it still is trying to pop but not really running. It seems to try to run on one cylinder or the other. I am wondering about the carburetor which draws from a common fuel line. It may be that which ever cylinder fires uses all of the fuel and starves the next cylinder. The plans show a crankcase vent system which I do not really understand. This may be to prevent one cylinder from starving the other cylinder. I may try making a fuel feed from two points to see if that helps. Any other input?

 

[Parksy]

This may be an obvious question, but have you played with the ignition timing? Tried advancing the timing?

 

[Brian Rupnow]

Gus on this forum has built, I believe, the same engine, and has encountered the same kind of problem. You might try corresponding directly with Gus and get his opinion. Gus is a very nice fellow, and I'm sure he would quite willingly help you out if he can.---Brian
http://www.homemodelenginemachinist.com/showthread.php?t=23975

 

[Gordon]

I have tried adjusting the timing and plan on advancing it some more. Just before I quit for their day I tried starting iit with my electric drill which runs faster and things look better. I have been in contact with Gus on Facebook and we both seem to be stuck at the same point. I think that I am getting closer.

 

[gus]

Gus on this forum has built, I believe, the same engine, and has encountered the same kind of problem. You might try corresponding directly with Gus and get his opinion. Gus is a very nice fellow, and I'm sure he would quite willingly help you out if he can.---Brian
http://www.homemodelenginemachinist.com/showthread.php?t=23975

Hi Brian,

Hopefully by end next week,I get V-2 up and spinning/Vrooming. Belief the gas intake is very tricky.Danger or too much and too little. For now I am no expert yet. Soon as I get V-2 spinning Gordon will the first to see it on FB.

Hi Gordon. Hang On.

 

[Gordon]

I have the engine running for 15 to 20 seconds. The problem at this point seems to be the carburetor. I have a temporary cobbled manifold running a model airplane carburetor. I am working on a better manifold which I am hoping to use with just one of the original carburetors. In looking at pictures and videos of the v2 and the v4 it seems like more folks have had carburetor problems because probably half of them are using some other carburetor from vapor carburetor to aircraft carburetor. It is interesting because the v4 uses a single carburetor on a mainiifold and the v2 uses two carburetors. George Britnell who has built a very similar v2 uses a single carburetor of his own design. Is George's design available anywhere?

 

[gbritnell]

Gordon,
I have been following some of your latest posts and I'm sorry I haven't responded sooner. I have built some of Jerry's designs and can honestly say that they are tried and true projects. That being said I know the V-twin has dual carbs and the fellows that have built one seem to have them running ok. Why do you want to go with just one carb?
My V-twin like Jerry's is a 90 degree twin. Mine has a single ignition with a waste spark. The only problem I ran into when running mine is that the heat from the heads gets transferred to the intake manifold and then to the carb. Once the carb gets hot enough it will boil that fuel back into the fuel line away from the carb (vapor lock) and the engine would start to run erratically. To alleviate this problem I made Corian spacers/inusulators to go between the manifold and heads. Contact me directly by sending a message and I will send you the drawing for my carb if that's the way you want to go. It looks like the breather/reservoir on Jerry's engine is a dual purpose. It vents the crankcase (which is necessary) and it has a small reservoir at the top to distribute fuel to each carb. My engine has the fuel tank level just below the needle valve on the carb so it doesn't flood when the tank is filled. The engine running will then pull fuel from the tank until it runs dry.
Here is a video of my engine running.
https://youtu.be/FTtyO_voUU0

 

[Gordon]

George: I have tried the two carburetors as per the drawings and have not even been able to get more than a single pop. Going with the airplane carburetor I can get 15/20 seconds. Part of the problem is that as you said the vent/reservoir is probably a vital part and I have been trying to get the engine running long enough to do the final spit and polish and final assembly. Sometimes trying to take a shortcut ends up being more work in the end.

Is your carburetor the same as shown as Ripnow/Britnell on home shop machinist? I just did a search and found that. I have not seen that site until now. Guess I will have to take another look.

Excuse the dumb question by why is the crankcase vent necessary? In looking at other pictures and videos of this engine many others have it running without the crankcase vent.

 

[gbritnell]

Gordon,
It's not a dumb question at all. The configuration of the engine is such that both pistons are going up and down (to some degree) at the same time. When this happens it builds up a lot of pressure in the crankcase. The down side of this is that the pressure has to go somewhere so it forces oil out of any clearances on the engine be it the crankshaft bearings or the piston rings. I had to lengthen my breather a little because when I would rev the engine quite high it would push oil up the tube and onto the crankcase. Now it only does it once in awhile.
As far as the carb goes here's a quick history of my carb designs. I started out making hit and miss engines which only required a venturi and needle valve because they were pretty much fixed speed engines. When I got into multi cylindered engines I didn't have much of an idea of what to use. The first thing that came to mind was using an RC airplane type carb and I thought that by purchasing one with multiple adjustments would make my engines easier to tune. I found this wasn't so. I saw that some fellows were using ultra small 2 cycle carbs like the type that come on weed eaters and such. I contacted those who were using them and found out it wasn't just a bolt on affair. I did the modifications necessary and still didn't have much luck with them. I went back to the model airplane type carb but to the simplest design, the air bleed type. This carb uses a cylindrical barrel with a cross drilled hole to form the venturi. It has 2 valves, one is a needle type which controls the fuel flow and the other is just a screw type which controls the air bleed volume at idle and low speeds. I have since eliminated the air bleed screw by adjusting the size of the air bleed port to suit the engine I'm using it on.
From following Brian's work I know that he had been using a carb based on Chuck Fellows design. I don't know if he still does. My carbs are all air bleed types. The most important thing when using a model airplane carb is to get the smallest one you can find. It's amazing how little air these tiny engine need to operate. The second thing to keep in mind is that the needles on these carbs are meant for methanol and therefore have a coarser adjustment range than required by our engine. That is why I make my own. The are basically the same as a model airplane carb in design but have very fine threads and much sharper tapers on the needle valves.
As I stated, contact me and I will send you the drawing for my V-twin carb. I don't want to post my email address out in the open due to spammers.
gbritnell

 

[Brian Rupnow]

I made a carburetor based on Chuck Fellows design, and it worked quite well. I made a carburetor based on George's design, and it worked quite well, although it did have a lot more work in it than the Chuck Fellows carburetor. The carb which I use now on most of my engines was originally designed by Malcolm Stride on his "Jaguar" and "Bobcat" engines. I'm really not sure that the "air bleed" screw does all that much, although George's and Malcolm's first designs both had them. I have used carburetor similar in size to George's design and Malcolm's design on both single and twin cylinder engines, and they work equally well on either. Chucks carburetor might be a bit small for use on a twin, but I have never tried it on a twin.---Brian

 

[Gordon]

Well it looks like I finally am on the right track and as usual it is just some simple thing. I was not getting enough suction and the fuel was not vaporizing properly. The problem was that I did not have the spark plug hole tapped deep enough so that it was leaking around the spark plug. I kept working on the valves and head sealing and nothing seemed to be making any difference. I finally squirted some oil around the spark plug and got bubble when I turned it over. One cylinder was pretty much OK but the other one was leaking quite a bit. I had enough suction so that I could kind of get it to run but since it was marginal it would not run well enough to keep running. Now on to actually finishing the engine. I built the Britnell/Rupnow carburetor and the seem to be working now that I have the compression suction issues taken care of.

 

[Brian Rupnow]

Gordon--Congratulations on having a runner. Is there any way you can put up a video for us to see?---Brian

 

[Gordon]

I have never taken or posted a video but I think that I can do it with my phone or my Kindle. At this point I have to take the engine apart again for a couple of things so I do not have any oil in the crankcase so I do not want to run it for very long.