Nemett Jaguar--Canadian Style

[Brian Rupnow]

I have spent the last week looking at model engine plans. The Nemett Lynx is all the rage right now, and I will be following all of the builds that are currently happening. However, as nice as it is, I prefer to see a lot of the moving parts in action,i.e. pushrods, rocker arms, etcetera. The one thing I don't like about the six internal combustion engines I have built so far, is that they all have open crankcases, and they sling oil all over the place. I know that quite a few have built the two cylinder Nemett Bobcat. The Jaguar is basically the Bobcat with one cylinder lopped off. It has exposed pushrods and rocker arms, but the crankcase and timing gears themselves are totally enclosed. It appears to have "splash lubrication" for the rod and the main crankshaft bearings. I have a copy of Malcom Strides original metric drawings, and I an going through them and modelling them in 3D solidworks, from which I will create my own detail drawings in British Imperial "inch" dimensions. I have already found mistakes in the drawings, so it definitely pays to model everything first. After I get the modeling finished, then I will step away, have a good look at what I have done, and then make changes which make sense to me. There will definitely be changes, and yet, by and large it will still be Malcom Stride's engine---with a Canadian touch.---Brian

[Brian Rupnow]

Well there!!!---That's enough silliness for one day. I have modelled 13 parts and one assembly since 6:30 this morning. It's a nice day outside, time to get out my 1931 Ford roadster and go for a little tour.

[Brian Rupnow]

Now I need help from anybody who has built this engine or the Bobcat. (They have the same cylinders and heads). The drawing of the cylinder head which I have has a fold right in the center of the drawing, and I can't make out the diameter of the large counterbore on the cylinder side of the head, and I can't tell the depth and diameter of the shallow counterbores for the valve guides.---I don't have a clear dimension of the cylinder i.d. either, only I assume it is 24mm, same as the o.d. of the cylinder liner.---Brian

[Jasonb]

The large counterbore fits over the flange on the liner so is 26mm dia x 0.5mm deep, leaves a 0.5mm gap between head and cylinder outer

Recess for the valve is 10mm dia x 0.5mm deep so the valve guide ends up flush

Yes Cylinder jacket is a light push fit over the 24mm liner, though I went with 15/16" so I could hold the liner in a 5C collet to face off the top flange.

[Roger B]

That design looks quite close to my vertical engine (except mine is water cooled). I will be watching with interest 

[Brian Rupnow]

Well, I got my question answered and kept on modeling. This is a section view of the current state. I don't have any bearings in yet, and I'm not sure about the location of the flywheel, as I haven't modeled the tapered bushing that locates it yet. I am quite surprised at the number on mistakes I am finding as I work my way through this. I am certainly glad that I just didn't accept the drawings as being correct and start machining. I couldn't understand why the cylinder has a liner in it. Now I see---it shows up in the section view. At bottom dead center the piston skirt extends below the cylinder by quite a bit. There is an assortment of ways to get around this, but so far I am modeling exactly as per the drawings, (except for mistakes that I keep finding and correcting).

[Jasonb]

You have the sump in upside down, should not have assembled as the square corners won't fit the rounded corners of the hole in the crankcase and the sizes don't allow it. The holes in the top of the cylinder only go through the top flange not all the fins. There should only be 5 holes in the head/top of cylinder not the six you have drawn, they are also on a different PCD to the bottom six, looks like the bottom ones are on too small a PCD. The bore in the back of the flywheel should be far smaller than you have it so will be loosing a lot of flywheel weight.

I wonder if some of the "errors" you seem to have found are actually where things clash due to your drawn parts not being as the plans show them?

The iron liner stops the engine being too heavy as the whole cylinder does not need to be iron, better wear surface than alloy and the alloy is better at loosing heat, not just a length issue. And on the water colled version you can easily hollow out the jacket and insert the liner to leave a waterspace.

J

[Brian Rupnow]

Okay--a few admissions to make. I read through the 42 pages of build notes last night (which, by the way are excellently done) and realized that #1--I have the sump bolted on upside down. #2--their is a different bolt circle in the bottom of the cylinder as opposed to the bolt pattern in the top. #3--Something is said about the rocker arms being right and left hand which I had completely missed. Once I take all that into consideration, there are far fewer mistakes in the drawings than I originally alluded to. The drawings I have all appear to have been scanned by folding in the center to get them small enough to copy on a scanner, and every damn one of them has missing dimensions right at the "fold".--And its amazing how many parts were drawn right in the center of the drawing where the fold is. I hate it when there is no overall general arrangement to see how the myriad of pieces all fit together. With this engine they supply a lot of very good photographs with the build notes, and I guess you have to suss out how all the parts go together by finding them on the photographs.--I'm not accustomed to working like this. George you are right---the piston crown is far too thin as drawn, as are many other parts, (in my estimation). First thing I will do today is correct the model, second thing is to return a phone call to Toronto about some "real work" I was asked about bidding on.---Good eye Jason.--I see you found all the things I did last night. Thanks for helping guide me thru this.---Brian

[gerritv]

First thing I will do today is correct the model, second thing is to return a phone call to Toronto about some "real work" I was asked about bidding on.----Brian

Making that choice of sequence is the secret to successfully transitioning to full retirement. Hard to do at first but it gets easier :-)

Gerrit

[Jasonb]

As the drawings have only really ever been published in a magazine they will all suffer with folds/staples in the middle.

David Clarke, the then editor of ME took the decision to keep the drawings to their original A3 size by printing over two pages which kept all the parts at full size rather than reducing down to fit an A4 page which results in small drawings like the Lynx ones published in the Best of ME III.

Had Malcom not met an untimely death he would have sold the drawings as A3 that is why they are laid out to suit the sheet size and also done any revisions as required, the ones in the mag are direct copies of his unpublished and untested drawings. If you read the correspondance on ME forum at the time the Bobcat/Jaguar was published these few anomolies were all picked up and had he been able these would have been incorporated in the drawings.

There were several 3D views on drawing #1 which was never published in the mag as a drawing. Instead the coloured versions appear early in the article and these are the general arrangements

Interesting your thoughts on the piston crown and other parts being thin, I'm slimming a few parts down as it is a bit of a bulky box and would go even further if I did not wish to keep it as a Nemett style engine.

J

[Brian Rupnow]

Gradually I am getting this sussed out. The modeling is almost completed. I haven't done anything with the timing gears yet. You see one section taken thru the engine at the center of the cylinder, one section taken thru the center of the engine at the camshaft, and one blow up of the rocker arm area. Something is very fishy with the crankshaft. The bill of material calls for 3 main bearings (in red) all with a 10mm i.d., but the center bearing is setting on a portion of crankshaft that is called up as being 12 mm diameter. The crank is a tad short on one end too. I will read thru all of the design notes tonight and see if I can pick up any clues.---The original designer MAY have meant the center bearing to be 12mm i.d which would make the crank correct in that area, but the crank would still be a bit short on the left hand end. The section thru the camshaft looks okay at a quick glance, but I may be missing a spacer on the right hand end to help position the bearing.

[Jasonb]

As I said read through the threads on ME forum, the bearing spec has been covered, you want a S61801 which is un shielded, 12mm bore,21OD, 5mm thick

Spring keeps are upside down, the spigot fits inside the spring, the e-clip in the recess

[Brian Rupnow]

Didn't get much play time today.--Worked all day on that small contract I went to Toronto to see about yesterday. I did manage to get the correct mod 0.8 gears downloaded and installed. When I get to my build, I will be using 24DP gears because that's what cutters I have.

[Brian Rupnow]

I am finished modeling the Jaguar. It seems to be a well thought out engine, and I am confident that it will work as designed. The drawings are somewhat difficult to read, due in part to the fact that when they were photocopied there are dimensions missing right at the crease in the centerline of the drawing, and there are a few minor errors. On top of that there is the fact that without a completed general arrangement it I found it very difficult to figure out where some of the parts actually went on the engine. As I understand things, Malcolm Stride created the first draft of these drawings and then unfortunately passed away. --It's pretty hard to go back and tidy up your original drawings once that happens!!! I haven't bothered with the exhaust pipe nor with the carburetor, as I will not be using the ones in the original drawings. There are a lot of things that I like about this engine. There are one or two things that I really don't care for, but they are cosmetic. I really don't like the square box shape of the crankcase--it looks like something you would find on a Russian tank!! The nicely rounded profile of the cam chain cover doesn't go with that box shaped crankcase. However, as I said, these features are cosmetic and will not detract from the running of the engine. now I will resave all of the files as a different part name and begin to make the changes I want.----Brian

[Brian Rupnow]

The Jaguar is morphing into something else----