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    Re: Re-engine Buggy with a (modified) Predator 670
    #31
    Millenium Member
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    Nov 2006
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    Lansing, MI
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    Way to keep after it! You've got a lot of good info in here to help people using the Predator engine(s).
    I race, therefore I am
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    Re: Re-engine Buggy with a (modified) Predator 670
    #32
    Senior Member
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    Sep 2014
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    West Palm Beach FL
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    So what you're telling me is there will be no 5 minute long donut sessions? lol
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    Re: Re-engine Buggy with a (modified) Predator 670
    #33
    Member crazy's Avatar
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    Dec 2007
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    Douglasville, Georgia
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    76
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    Got any Videos?
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    Re: Re-engine Buggy with a (modified) Predator 670
    #34
    Senior Member darwinpayne2000's Avatar
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    Jan 2010
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    American Fork, UT 90 minutes from the sand
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    No videos yet. The trails have been full of mudholes, so the rides have been less than exciting, unless you like to see a bunch of water splashing all over the driver (and the camera). I'm hoping to get back out this weekend, but I discovered that one of the brake rotors is . . . damaged. Like big time. Ripped off the hub. I'm not sure how that happened, but I need to investigate. Hopefully, I have a spare rotor. The alternative is ordering a replacement and cooling my heels for 3-5 days.

    As for making progress on the engine mods . . .

    The next step is to modify the exhaust. I'm not expecting huge performance gains just from modifying the exhaust. The Predator muffler is fairly large and free-flowing, especially when you compare it to the stock Vanguard muffler, so there may only be some modest performance gains right now. Once I install a new carburetor, however, I think the freer-flowing exhaust will be a bigger benefit.

    I reversed the exhaust flow on the stock muffler because the direction was towards the front of the buggy. I capped off the original exhaust port. One option for more flow is to open the capped port back up and have two exhaust ports. It's now bidirectional inside, so both ports are viable. I could add an exhaust pipe with a 90 degree bend in it to direct the exhaust downwards instead of into my left ear. Do the same trick on the rear exhaust so they match.

    Another option is to go with an exhaust header and a new exhaust pipe/muffler. I've seen Predator 670 exhaust headers on sites that cater to the boating crowd. The pipe layout works for a boat, but not really a great layout for a buggy. I could make a set of headers, but my tubing bender is set up for 1" tubing and the exhaust is 1 1/4". I looked at the cost for the 1 1/4" bender dies and it's . . . $350. Ouch!! I can buy a lot of mandrel tubing for that price.

    If I don't go with a simple mod of the Predator muffler, then I may go with a dual exhaust setup. I had dual exhausts on my old Briggs engine and it actually sounded really cool. Most people commented that it sounded kinda rough-and-tumble, like a V-8. The mufflers were home-made from plans that Scott at Ubuilditplans sent me. I wondered if there was a better muffler design out there, but after researching a few websites and watching a few Youtube videos, I decided that I would reuse the plans Scott sent me to make new mufflers. Slightly bigger and longer to accommodate the 1 1/4" exhaust tubing. I can pick up a piece of 90 degree 1 1/4" exhaust tubing for about $10 online. Not too bad when you consider that two 90 degree bends would cost me $175 each if I bought the new bender dies.

    Here's a couple of pictures. The first picture is one of the mufflers off the old Vanguard engine. The second picture is a Walker muffler that has 1 1/2" intake and exhaust. Walker has these 6-inch round mufflers in various lengths and different intake/exhaust diameters and one idea is to make a mini-header and run it into one of these mufflers. More tubing, but maybe better to have a large single exhaust instead of two exhaust pipes.
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    Re: Re-engine Buggy with a (modified) Predator 670
    #35
    Keeper of the Asylum K-fab's Avatar
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    Jun 2006
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    Scottsdale, AZ. 10.9 miles from the trailheads
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    I’d go the single large route.
    Probably weighs less, is easier to package and is one less exhaust pipe to have go wrong.
    the dual setup does look good, though.
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    Re: Re-engine Buggy with a (modified) Predator 670
    #36
    Member crazy's Avatar
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    Dec 2007
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    Douglasville, Georgia
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    I had a similar size go kart with a V twin engine. Seeing your buggy makes me want to build another one. The torque of the V twin engines on such a small frame makes riding a lot of fun.
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    Re: Re-engine Buggy with a (modified) Predator 670
    #37
    Senior Member darwinpayne2000's Avatar
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    American Fork, UT 90 minutes from the sand
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    No direct progress on the muffler/exhaust setup yet, except I decided to open up the forward exhaust pipe and put a 90 degree bend on it. Since I'm not making any real engine modifications yet, there's no hurry to build a "killer" exhaust setup. However, I did find some 1 1/4" exhaust tubing with a tight mandrel bend on summitracing.com. $20 (and some change) each.

    Before I get too deep into this project, I need to put some "break in" time on the engine. The manual recommends that you not run the engine at maximum rpm during the first three hours of use. Well, that ship has sailed, but I do want to get a few more hours on the engine and get towards the end of the "maintenance" mode (the first 20 hours) before I start making significant changes.

    I did a quick check on the buggy and discovered that the right-rear brake rotor was . . . destroyed. Ripped right off the hub. Something was definitely wrong there. I was hoping that I had a spare rotor and I was pleased to find that I had a new pair of rotors in my spare parts bin. Except, the new rotors are 7" and the old rotors are 6". Not a direct fit. Obviously, I bought the new rotors as an upgrade. I recall thinking about replacing those tiny 6" rotors with something bigger, but I never got past the "ordering parts" phase.

    The new rotors would require moving the brake caliper bracket, so I thought I would keep running the existing brakes for a little longer. I checked online and a replacement rotor is $40-45. Ouch!!! A lot of money for something so tiny. I also didn't want to wait several days for the replacement rotor to arrive, so I decided to make my own rotor out of some spare 1/8" steel plate.

    All-in-all, it turned out fairly well. It's not perfectly round, but that isn't necessary, since the calipers grab the rotor at an equi-distance from the axle, not from the outside rim. Good enough for a temporary rotor.

    When I put the axle back together, I discovered that the spacer between the rotor and the axle bearing was too thick. It was keeping the rotor out of alignment with the caliper and that's what caused the rotor to bend and break off the hub. Lesson learned.

    I took the buggy out to Five Mile Pass yesterday and put some more hours on the engine. Unfortunately, the time was cut short when I tangled with a tree on a steep slope. The buggy just doesn't turn very well when I have the brakes on and I had a slow motion crash into a pinion pine. In the process of hitting, then extricating myself from the tree, I snapped off the steering arm on the left-front hub. That made for a fun ride down the rest of the hill, then back to the parking lot. I used my left foot to periodically kick/steer the left front tire. It mostly ran straight on it's own. I just had to keep the speed down and not get myself into further trouble. A broken spindle would have been the end of it.

    Here are a couple of pictures of the old and new rotor. I have some family vacations, etc over the next few weeks, so I'm not sure when I can get back to this project, but . . . soon.
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    Re: Re-engine Buggy with a (modified) Predator 670
    #38
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    Man I can't believe you didn't feel and hear that thing hanging up, to get a rotor to bowl like that takes a fair amount of heat. I wonder if your spacer wasn't the problem?

    I had a single piston caliper on a stuntbike that didn't slide on the pins like it was supposed to, so when I hit the brakes the piston would push the rotor to one side rather than pinch it. That caused it to bowl shape a little, but not as bad as yours.
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