Lengthening MTL F7 chassis to FP7?

Hello all,

Long time lurker, occasional poster here. With the recent announcement of Micro-trains SD40-2, it has inspired me to look closer to home for my prototype inspiration and model CP Rail.

I currently have a pair of MTL F7A's, and I'd like to turn these into an AB set of CPR F-units. I'd like to extend the chassis on one to create an FP7, and just put a B-unit shell on the other one.

Question is, how would I go about doing this? I know David f did something similar w/the GP35, so I know it can be done, any suggestions?

Cheers,
Dan MacKellar

 

that's going to be hard. you can cut the chassis and add space to lengthen it, but you may not be able to extend the shafts on the gearing to reach across the gap. when i extended the GP35 frame, all i had to do was make a new, longer pivot part (don't know what to call it) on the one worm gear shaft to make the connection.

MTLs F-7s have a more complicated gearing set up. you would have to be able to totally remove one of the worm gears (on end to be lengthened) and put it on a new, longer shaft (and then replace the connections). i'm sure it's doable if you have the tools. i've tried punching worm gears out of their shafts before -- with terrible results, because i tried it with a hammer, drill shaft, and hold in the work bench.

if you could get this (worm replacement) part done, the rest wouldn't be that difficult.

maybe someone else will have an idea, but that's the only i can see it happening (and still have both trucks powered).
dave f.

 

It would be a little bit harder than a GP35. The F7 has barrel gears for reduction.

Possibly since the worms have plastic bushings on each side that tab into the frame. You could just use a longer shaft on the side you lengthen. So you would have the worm, 2 plastic bushings, and part of the barrel gear all on a new longer shaft.

I don't have a F7 apart now, but NWSL makes small worms for a 1.5mm shaft. The worm would need to match the gear pitch of the worm gear though. Another idea is to extend the stock shaft with sleeving.

It may be easier to use a GP35 chassis under the shell, but that would be expensive.

 

Is the truck spacing on a GP35 correct for an FP7? Fuel tank problems?

Oops! Z scale! Still, the prototype info should apply. :happy19pb:

 

I meant it may be easier to lengthen a GP35 chassis than to lengthen a F7 chassis.

With either one the hard part is keeping the frame perfectly straight and in line while you fill the space left over.

 

actually, that is a brilliant solution. the GP35 chassis is longer (by about 1-1/2' (i think). it could be right on for the FP7! add a little weight to the sides (thin insulated lead sheet) and you'd have a better running (quieter/smoother) F7! even if the FP7 is still a bit longer, the difference wouldn't be worth worrying about.

yes, the GP35 chassis would be the way to go, in my opinion.
dave f.

 

My limited research indicates that the FP7 was four feet longer than the standard F7. Still, there must be some model with a wheel base 4 feet longer than the F7.

 

I have been thinking about the same thing myself. The GP35 would be close, but not exact.

F7 wheelbase is 30', an FP7 is 34', and a GP35 is 32'. If you don't mind 2' in Z scale, you could do it without chassis modification. It's too bad we don't have a GP40 or 50 or 60... All share the same 34' wheelbase.

Scott

 

The easist way to lengthen the chassis is with roll or solid pins. Disassemble the loco (remove truck, motor, etc). Either reassemble the two halves or work with them indendently. Clamp one or both in a drilling jig. Drill two holes into end (one above the other) long enough to hold a pin into the main center mass that will house the motor and truck bearings. Part off the end to extend the length. You must do this beyond the truck's outer most bearing area. Insert the pin and push the cut piece back on, leaving a gap long enough to grow the length needed.

 

FP7

I had the same idea when looking at options for our 35 chassis. I ended up taking the front end of an A unit and a B unit and splicing them together to get the right length...about as far as I got due to time and energy level. I had planned on making the chassis longer and got distracted doing the GP-60 by doing the same thing to a couple of 35 chassis and shells. I made molds and castings of the chassis and lengthened them in preperation for remolding and casting using metal filled epoxy with additonal brass powder added. I also intend to hollow out the fuel tank and add a small piece of lead or some exotic powder...but... To get the F unit to sit on the 35 chassis is not a problem, just make "U" shaped frames for the inside of the shell to help it sit right and not fall off. A couple of guys on this site have extended the 35 chassis to make GP-38's and the like, maybe they can chime in on some other techniques. The FP-7 was one of my early considerations for production, and maybe some day we will get around to it.

Cheers
Joe
MTL

 

FP-7

This sounds so much easier!!!!!

Joe

 

rail images is still down, or i could show you some pics about how i lengthened the GP35 chassis to make the GP40s. i did it just as jeff stated above --

cut in the middle of the bigger flywheel space (NOT where the motor terminals exit) and put pins high and low in the frame. with brass wire you can then bend/twist the parts to get them aligned perfectly. then J.B.Weld in the slot. i then used a dremel tool to smooth and finish and made a lengthened connector for the worm gear to the flywheel connection. the hardest part is cutting the frame halves.

dave f.

 

Thanks for the input guys. ATM, using a GP35 chassis isn't an option due to budget considerations (lengthening that is in the cards though, I've got an Undec Rogue GP38-2 shell here itching to become a CPR 3000 series.

Looking at my disassembled F7 here, the hardest part would be finding some place to put the pins as outlined in Jeff's example, there's not much material there.

Looks like extending the bell gear from the worm may be an option, possibly via sleeved connection and soldered. To still hold the trucks in place, it looks like I'd have to slice in front of the fuel tank about halfway through the bell gear housing and mill the added section out to fit the bell gear. That wouldn't leave much room on the top though. Possibly right ahead of the dimple for the truck closest to the fuel tank?

I want to be sure how I'm going to do this before cutting my chassis

**EDIT** Added image after looking at F7 chassis in regards to best apparent way to lengthen it.

 

What about using metal plates on the top and bottom of the center section instead of pins into the chassis body. Should be no issue with space for that in the fuel tank area even if the area has to be milled out and recessed. On the top you might have to use a longer plate to get enough mass in the chassis if it has to be milled out and recessed.

I'm very curious about this since using the F7 chassis for an FP7 and possibly some other loco kitbashes is in the long range plans for me as well. You can still get used or discounted F7 chassis almost two for the price of one even over GP35 chassis.

Randy

 

I think the pins concept by DanMack is the best, but I have used .005 styrene ACC'ed to the outside edge of the area where the frame half was cut. It forms a trough between the two cut frame halves. I put lead cuttings in the trough and add epoxy to hold the two pieces of the frame half together. Be sure to leave room for the motor shaft. After curing, I reassemble the pieces. Once inside the shell, there is no real stress on the two frame halves; it just sits inside the shell. I have done this to about five Kato frames.

Giving credit where credit is due: Jim Semikowski showed me this technique several years ago around 1990 when I was first stretching mechanisms to make a tunnel motor.

 

Randy, Flash, thanks for the info. David's idea of using JBWeld was what I was thinking, but I'm unsure whether to go with flexible pins (brass wire) or stiff ones. I suppose if I use the JB Weld it won't really matter. I may actually attempt this in a week or so (When I can get access to a shop)

I'll keep you guys posted.

Regards,
Dan MacKellar

 

an opinion ... if you have great milling equipment use hard pins (if you go with that method). the holes need to line up dead on. otherwise the brass pins allow you to manipulate the frame to align it correctly.

understand, that i work with basic hand tools at a simple work bench. i hand drill holes, and hand cut the frame. i need a "low tech" system to extend frames that doesn't require drill presses, lathes, milling machines ... because i don't have any of these. if you do have them so much the better! Joe D'Amato has a fantastic assembly of resources and personal skill -- we must all envy his ability to make a prototype that can become a master. i look forward to seeing the projects he's undertaking.

in short -- if you're limited to certain tools the brass pins "forgive" enough to produce a good result because they can be manipulated. my 2 cents.
dave f.

 

Quick update to this project, I haven't started on the frame yet, but the shell has been started. The surgery went well for a first try, although a slip of the scalpel caused one of the rivet strips to disappear on the joint. Nothing a little putty and styrene can't fix.

Next one I do will be a little different, but overall, I'm happy with the results.. Pictures coming soon. (probably showing the shell and the frame at the same time)

Regards,
Dan M.

 

we'll look forward to seeing them dan. i think you're the first to try to lengthen this particular frame. at least in my observation, but others who've been around longer would know better than i. still, i think this is going to be a good project to watch. go for it.
dave f.