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  1. #1
    RC Qualifier
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    Dec 2014
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    Backplate bearing mod

    I tore down my modded 3.3 to install in my offroad jato project. I noticed wear between the backplate and starter shaft. I only have about two gallons on this engine. I ordered new parts to replace them, thinking that this is excessive wear compared to the new 3.3 engine I'm removing. I was thinking about counterboring for a bearing to fit into the backplate. This should greatly reduce the wear rate on the bushing and shaft. Also using a quality sealed bearing would help with any possible leakage and last longer than the engine itself. I was only going to use one bearing and still keep part of the bushing intact. Has anyone tried something like this and have any advice? Is it worth it or not? I'm unsure on which side to counterbore, should I install on crankshaft side or install on the outside (starter side)? I'm thinking on installing on the outside because of machined smooth fit match on the inside.

    Another question: I'm also going to be using a RB mods turbo plug button head, running on Traxxas 33% fuel, have a Picco 7.5mm carb installed and going to drill out exhaust stinger. Any recommendation on O.S. plug temp to start with, (P3 P4 P5)? Also if I should change head shim thickness with the new head? Open to any ideas.
    Thanks,
    Grizz

  2. #2
    Marshal Double G's Avatar
    Join Date
    May 2008
    Posts
    13,536
    Here are my thoughts as I have not heard anyone doing this: you'll need a quality high-speed bearing and I would bore the outside and install there so that if there is failure there is a large chance the parts will eject into your starting system rather than mosh-pitting in the crankcase.

    RB recommends using hot turbo plugs so to me that means the P6. With the nitro you are running you may want to drop it down a little cooler to a P7 or P8.
    The Super Derecho

  3. #3
    RC Turnbuckle Jr. Nitronaught's Avatar
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    Oct 2005
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    South Florida
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    19,501
    Unless you are not able to hold a tune and that backplate seal is OK, the wear is nothing really to be concerned about. It's designed to wear. Me, I use recoil start, put's a lot less wear and tear on the shaft. IF you don't see fuel coming out the back end and it's holding a tune, run it.

    Bearing? If it fails, kiss your engine good bye. I do believe you can make the Jato "Bump Start"... But that's also a lot of extra stuff to lug around. Seen a few. Still boils down to the seal on the backplate and it not leaking outside the engine. Never been a problem for me and I've past 8 gallons. I have 4 engines. fired them up last week.
    All Lives Matter
    United We Stand, Divided We Fall

  4. #4
    RC Qualifier
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    Dec 2014
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    Adirondacks
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    304
    Thanks for the advice. I ran into another problem so the bearing mod will be put off for a while. Maybe this winter i can mod a backplate and have it on hand for future use. The new problem I created is I need to repair the carb. I ruined the sleeve(adapter) that I made when I was turning the carb into position for a better fit with the linkage. The original one I made was of soft plastic and flexible. This time I'll make it out of aluminum or stainless steel and epoxy it onto the carb. Should have done it this way the first time as the carb body is also plastic.

    Double G: I should have asked RB what plug to go with. I was hoping someone had experience running the button or the engine he used to make (3.7 RBMods TRX engine). Looking at an OS plug chart the standard plug for the TRX engines is the LC3-LC4 which looks like a match to P3-P4 turbo plug, but on another OS plug chart shows LC3 matches to P3 and the LC4 matches P6. It's a bit confusing.

    Nitronaught: Still held tune and ran great. I did/do have a little bit of oil residue on the outside of the backplate coming from the starter shaft/bushing area. Not soaked but noticeable. I also like the recoil start over the EZ-start. I only need to carry a small igniter. If I went bump start I don't think I would be able to enjoy the hobby as much as I do running a nitro vehicle, like you said "that's also a lot of extra stuff to lug around."

    It's kind of funny as I own a Summit and the e-revo 2.0 which are simple as plug and play, but enjoy my nitro vehicles much more.

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