1/8th Scale Offy Build

[Daytonatim]

Well, I figured it was about time I super sized my model building projects. Having limited space to display any models, I have always leaned toward 1/12th scale. But since I have a 1/8th scale TDR engine stand sitting finished with nothing mounted to it I figured I would buildup something to put on it. So, I figured I would do a TDR Offy.

I always had a lot of admiration for this engine. It is really hard to believe that they were building hemispherical head, 4 valve per cylinder, dual over head cam engines back in the 1930's. I guess that is why this engine had a 50 year run, holding its own, on the fastest race tracks in America.

This thread may also serve as an assembly guide for anyone building up one of these little gems too.

So, I figured I would start on the cylinder bank and block since everything hangs on these two components.

Block: The block went together easy enough. Since the joining seam is covered by other components on the engine I did not worry about filling it. The only place it may peak through is at the back of the block right where the cylinder bank mounts to the block. There may be about 1/32" sticking out from the cylinder bank so I did not worry about it.

Cylinder bank: This went together easy enough, just like the block. The only difference being that the seam running down the middle of the head is quite prominent and a bear to fill in because there are 6 water jacket outlet ports located on both sides of the seam. These jackets made it pretty tough to sand away the epoxy and superglue that I used to fill the crack. So, I took this to heart and the next day I fired up the ole computer and modified the the TDR Offy file. Now when you order the TDR Offy you will receive the kit with a onepiece cylinder bank and a one piece block. So now there there will be no seams at all to work on, on these two parts.

Now, as far as surface finishing goes, I started out using a brass wire cupbrush in my dremel tool but found that it left a black residue on the parts. I did not know if this would be a problem, so I switched to a carbon steel cupbrush and it worked just fine. I am using my cordless dremel tool so I can turn the speed waaaayyyyy down. That way the part does not go flying out of my hand and I don't hook any edges and accidently grind them off.

Also, I found that using a green Scotch-Brite pad worked real good getting around those details. I found it to be good for removing some of the "sand cast" finish of the raw parts and for smoothing up the primer paint I used too.

I did not want to make the engine block glass smooth. I wanted it to have a little spotty roughness to it, especially in the crevices. I am going to try to do a dark wash on it as it nears completion and I figured the crevices would help grab the wash and add to the detail in these areas. We will see.

I have never done a wash before, so if anyone has any helpfull hints or tricks please speak up.

Oh, also, I found that the rapid prototyping material, that TDR uses to construct these models, behaves just like resin . It sands and feels very much like the resin part I have worked with in the past. Truethfully, once you smooth up the surfaces, you would be hard pressed to tell it from resin . Oh, and I did not bother soaking the parts in Wesley's Blech White for parting compound removal. There is no parting compound on these parts. I just wiped them down with mineral spirits before painting and I have had no problems thus far.

Well enough of the talk, here are some pics of the block and cylinder head.

[whodaky]

Looking good Tim. Can't wait to get mine and see it first hand. I have an idea for a project, I hope that when the engine arrives that it inspires me to run with that project.
I like the fact that it was so easy for you to do a redesign on the production piece to make the engine more user friendly in it's construction.
Thanks Geoff aka whodaky

[Daytonatim]

Looking good Tim. Can't wait to get mine and see it first hand. I have an idea for a project, I hope that when the engine arrives that it inspires me to run with that project.
I like the fact that it was so easy for you to do a redesign on the production piece to make the engine more user friendly in it's construction.
Thanks Geoff aka whodaky

Yours will be the two piece design, since I just made the mods the other day. If I can smooth out the seam though, anyone can.

Yes, it was very easy to make the mod. That is one thing that is really cool about this process. Nothing is ever set in stone......er.......I mean silicone.

[sydeem]

I have a few questions and I am really glad to see you building the kit so I can follow. I laid out the parts against your posted kit pictures and found a few (last picture) I could not quickly identify. Can you show where they go?

I was afraid to use the dremel cupbrush for smoothing as I tend to overdo everything so I bought the vibrating pencil sander from MicroMark. As the Offy (I believe) was machined I hope to make a glass smooth finish for all the outside surfaces. This will be very difficult on the small parts. I had begun sanding the major surfaces but there is so much detail that has to be sanded that I felt the vibrating tool was essential.

I will be going slow on this build as after twenty years of retirement I decided to go back to work (as a census lister!). Kind of a shock to the system to be busy 40 hours per week.

[Rick]

Syd........Here's some photos of my 6th scale Offy. Hope they help you with some of the detail parts and colour. If you need any more photos, let me know.

[sydeem]

Thanks Rick - those pics are just the thing.

Oops - I also woke up in the middle of the night and realized much of the Offy parts had to be castings not machined or there would have been too much wast. It has been 60 years since I last saw an Offy and I just remembered they had clean and shiny surfaces but the largest parts must been castings.

[Don Garrett]

Syd, there were a lot of variations of this engine built so there is room to play, the way the TDR kit is set-up you can switch the exhaust and injectors from side to side to suit your own particular build. I've seen them both ways. Same with the water inlets, there are six but you will only use 3, the kit has 3 block off caps for the the 3 you don't use....correct me If I'm wrong about this Tim or M.F.

[Daytonatim]

Syd:

I have an animated instruction movie that will show the assembly of the Offy. I will complete it next week and will be posting it up on YouTube. I will link to it in this thread and I think it will go a long way in explaining a lot how to put the Offy together.

In the meantime though, the unidentified parts in your pic are: (from left to right, top to bottom)

1 Crankshaft output front
2 Crankshaft output rear
3 Caps that go on the ends of the cam cover or cam drive cover
4 Cylinder brace (goes at the top of the cyl bank at the back edge
5 Oil outlet flange covers (on both sides of block, bottom front)
6 Fuel pressure regulator ( goes on the mounting arm on injector part)
7 Magneto drive cover flange (not sure which, there are 4 total two with center holes two without)
8 Same as 7

Oh, also, when sanding around those details you mentioned, try using the Scotch-Brite scouring pads, the really work well in these areas because the do not affect the details really at all.


Hope this helps some for this weekend. I will get the movie out early next week.

Tim

[Daytonatim]

Well, I got a little work done yesterday and some this morning. Thought I would post up some pics

I know I am a "Johnny Come Lately" to the modeling world so everyone probably known this since dirt was invented. I was trying to come up with a way to make bolt heads cheap. We do not have a hobby shop in town so I do all my hobby shopping at Lowes. I found some 18 gage tacks that had a rounded head on them. I though that maybe I could grind some flats on them with my dremel tool.

I just needed to find a good reliable way to index the flats so I get a nice 6 sided bolt head. Well I went down in the garage and found a 3/4 inch nut that would tighten up on my pin vice. So I just put the tack in my pin vice and rested the flats of the nut on my work surface and lightly touched the grinding wheel spinning in the
dremel tool. After I was done I "painted" the bolt head with a Sharpie marker and then cut off the tack so it was about 1/8" long. Then I just inserted them into the boltholes on the cover plate. Once I got the process down I could do a bolt in about 1 minute. So 97 cents got me about 500 bolt heads that I can vary in size. I found that once you painted the bolt heads black, any inconsistancies in flat size could not be seen as long as there were close.

Well, enough talk, here are some pics. Happy Easter everyone.

[Don Garrett]

Havin' some fun now, huh Timmy?