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    Re: Re-engine Buggy with a (modified) Predator 670
    #11
    Senior Member darwinpayne2000's Avatar
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    So, a couple of notes:

    The manual that comes with the engine is fairly decent. Along with the usual helpful warnings, such as "the failure to fill the engine with motor oil will void your warranty", it also includes the specs for the engine, including the valve clearance, spark plug type, oil filter number, etc. One of the few manuals worth keeping.

    Speaking of warnings, there is a little tag attached to the dip stick. I assumed that the tag said something like "This is a dipstick. Use it to check the oil level." Instead, it warns that the engine still has a half-quart of oil in it, from testing the engine at the factory. If you assume that it takes two quarts to fill it, as the manual states, you'll overfill it.

    . . . and now back to the issue with the backwards exhaust pipe. I fired it up this morning with a minimal amount of coaxing. The engine comes with a 90 day warranty, so I wanted to make sure I put some hours on the motor before the warranty expires. I'll be running it off-and-on until I get it out on the trails in a couple of weeks.

    If you sit in the buggy with the engine running, you get a nice, hot breeze right on your left ear from the exhaust. Fun.

    I suspect that the muffler is basically a "can" and that the exhaust direction is determined by the end cap. (I'm sure they try to keep it as simple as possible on the assembly line.) If I plug off the front and drill out the back, it will probably work exactly the same, just as Neo suggested. The only issue is that modifying the muffler would "void" the warranty. I really wanted to test it with the stock exhaust before I install a custom system, so I might just go ahead and make the mods and test it out.
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    Re: Re-engine Buggy with a (modified) Predator 670
    #12
    Senior Member darwinpayne2000's Avatar
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    I need to shift away from installing the Predator engine to upgrading the drivetrain.

    With the Vanguard engine, I was running #40 chains between the primary and secondary jackshaft and from the secondary jackshaft and from the secondary jackshaft out to the axles (dual chain setup). I've always stuck with good quality chains, so I didn't have any issues. However, with the Predator engine, I will be bumping up the horsepower and I want to make sure that the drivetrain can handle it.

    The chain between the primary and secondary jackshafts is a dual-strand #40 chain. I originally had a single-strand chain, but it was really wearing out the sprockets. I thought of replacing it with a #50 chain, but Scott at ubuilditplans pointed out that the #50 chain would generate a fair amount of heat due to the short length and the size of the links. The solution was a dual-strand #40 chain.

    I will be keeping the dual-strand setup between the jackshafts because the chain has a tensile strength of 8000 ft-lbs, which is roughly the same as the 530 chains that I will be using. The chains from the secondary jackshaft to the axles will be a pair of 530 o-ring chains. I'm using 530 rather than 520 because the #50 industrial sprockets are easy to find and a 530 chain is the same width as the #50.

    So, give me a few days to get the drivetrain sorted out, then I'll be ready to start testing the engine.
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    Re: Re-engine Buggy with a (modified) Predator 670
    #13
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    Would it not be a good idea to give it a try with what you have first? In case you need a gear ratio change?
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    Re: Re-engine Buggy with a (modified) Predator 670
    #14
    Senior Member darwinpayne2000's Avatar
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    Using the existing drivetrain for testing was Plan A. However, the left sprocket on the axle got chewed up when the chain tensioner broke and the chain slipped on the teeth. I don't have a spare rear sprocket and the buggy tends to go a little squirrel-y when you run it with just one chain, so I decided to push forward with the upgrade.

    Is it possible that I might need to go with a different gear ratio? Possibly, but I've been using 8:1 for years with the Vanguard and it seems to be a good ratio.

    If I make any changes, it's more likely that I'll make changes to the Duster clutch to tweak engagement, downshift, etc.
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    Re: Re-engine Buggy with a (modified) Predator 670
    #15
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    Oh ya! You did some damage there..lol
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    Re: Re-engine Buggy with a (modified) Predator 670
    #16
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    Just a thought...might not be worth the effort but just putting it out there...

    that’s the same kind of rear suspension setup as you find on the Roketa GK-13. Instead of a tensioner the GK-13 trailing arms have an eccentric hub...you use a spanner to turn the hub to tighten the chain. You can find GK13’s all over the place for pretty cheap...there’s one in my neck of the woods for $500 I’m considering getting to swap a real motor into (they can handle about 100 horsepower). You might be able to find a busted one near you that you could pull the arms off of. Might be a bit of work, but would be a very reliable way of eliminating future tensioner problems from stranding you.
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    Re: Re-engine Buggy with a (modified) Predator 670
    #17
    Senior Member darwinpayne2000's Avatar
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    My Polaris ATV's also use an eccentric hub to tighten the chain. It's a fairly good design.

    The rear trailing arms are based upon the Shredder II plans. Scott designed the rear axles to slide forward and back to tighten the chain, but it was problematic to keep the axles aligned with the chain and keep them from moving around over time. I made the axles fixed and added a chain tensioner. That actually worked pretty good and the tensioner wheels were really cheap. They're just the hard plastic wheels from a set of casters. They would also last a fairly long time.

    Last time I worked on the rear-end, I had a new set of tensioner wheels, but I decided that I could get a few more miles out of the existing wheels. Bad mistake. The wheel on the left-side broke and that allowed too much slop in the chain. The chewed-up sprocket was the result. In retrospect, I should have gone ahead and replaced them. The wheels barely cost $4 each. Instead, I get a $40 sprocket chewed to pieces.
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    Re: Re-engine Buggy with a (modified) Predator 670
    #18
    Senior Member darwinpayne2000's Avatar
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    So, I've made some progress on the rebuild. When you start one of these projects, you need to figure out how long it will take, then double it, then double it again when you're halfway through. Some tasks are time-consuming and tedious to finish.

    The front engine supports now come down from the new cross-brace, instead of extending down onto the frame in front of the secondary jackshaft. Removing and installing the jackshaft is much easier now that I have some room. I applied some fresh paint to keep the new metal from rusting. The buggy needs to be stripped down to the frame and repainted and that will happen, but not today.

    The sprockets and chains are also installed. I picked up a 10ft length of dual-strand #40 chain off Ebay a few months ago for a cheap price. I'm running a fairly short chain from the primary to the secondary, so I have enough leftover chain right now to last a lifetime. I'm using #50 industrial chain from the secondary to the axles. The chain was surplus from an earlier project and I want to be sure that I have the right gear ratio before I start cutting up some expensive o-ring chains.

    The throttle cable is also hooked up. It's somewhat jury-rigged because the ultimate goal is to replace the stock carb with a 38mm flat-slide that's sitting on my shelf. No point in fabricating a new mounting bracket when it will be replaced in a few weeks.

    The tasks left to finish are:

    Move the ignition switch from the engine to the panel below the steering wheel and extend the wires. It looks fairly easy, just another one of those time-consuming tasks.

    Reverse the direction of the exhaust from the muffler. I have a 1 1/4" hole saw and some tubing. Just drill out the endcap, weld on a short piece of exhaust pipe and cap off the existing exhaust port.

    Mount the gas tank. I have to move it to the right about two inches to clear the Predator engine. Fun.

    The challenge is getting all this done today while packing up to go camping (and take the buggy along for a test ride). Lots to do, not a lot of time for doing it.
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    Re: Re-engine Buggy with a (modified) Predator 670
    #19
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    Hoping to see some drifting footage..lol
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