1984 SurfJet!
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Thread: 1984 SurfJet!

  1. #1
    PWCToday.com Is My Home Away From Home delagem's Avatar
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    1984 SurfJet!

    I picked up a 1984 SurfJet 336 Freestyle, the shortest of the SurfJet boards. I've been looking for one for a few years now, but it seems that most sellers think these things are gold-filled, or something. I finally found one cheap enough that I figured it was a decent deal; I paid $300 for this one.



    The stock SurfJets should weigh between 125 and 135 lbs. Any more than that, and the board is waterlogged. It's easy to weigh, just bring the bathroom scale out to the garage, flip the board up on its nose, and weigh it. This one weighed in at 162 lbs, way overweight. Let the refoaming begin!

    You would think the easiest way to open the board up is to pry it apart at the seam between the yellow upper deck, and the white, lower deck. But the board is held together by 5200 or some similar adhesive; attempting to open the board in this fashion will result in fiberglass splinters and a wrecked board.



    Instead, I cut my board open with a circular saw. Make sure the back cut is done 2" in front of the engine doghouse, otherwise you'll risk severing the tube holding the hydraulic throttle.

    A circular saw set to about 3/8" depth works well for cutting the deck open. A shovel is absolutely the only way to take this foam out.





    Attached Images Attached Images
    Last edited by delagem; 04-24-2011 at 09:00 PM.
    '58 Vincent Amanda Water Scooter, 0rpm, 0mph

    '84 SurfJet 236ss Freestyle, 5950rpm, 24.6 mph

    '91 Jetmate! SX-R 800,GroupK carbs,R&D 26cc head,R&D ProLok F/A, Coffman Rocket Pipe,Impros 13-20,76mm nozzle: 6630rpm and 38.1mph GPS

    '92 SL650/750, dry pipe,extended pump,trim,HotSeat Waterbox: 6320rpm, 50.1 mph

    '00 SLX,Tau Ceti F/A's,NuJet prop: 6670rpm, 63.1 mph

    '03 Octane, Watcon 2318 CDI

    '04 MSX140,Impros stage 2 Powertune 14/23,WetWolf,6deg wedge: 6750rpm, 60.5 mph

  2. #2
    PWCToday.com Is My Home Away From Home Twinturbostang's Avatar
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    Re: 1984 SurfJet!

    Nice, a guy in my town has a few of them but thinks they are gold filled. I asked about buying one and he started with well they are real rare and hard to find soooo..... I said never mind!
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  3. #3
    PWCToday.com Is My Home Away From Home delagem's Avatar
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    Re: 1984 SurfJet!

    While you've got all the foam out, put the board up on sawhorses, with a bright light overhead. Look at the underside of the board, and you'll find out why your board is waterlogged. I found a bunch of tiny holes that were letting the water in. I circled them, and filled them with 2 part epoxy.



    While you've got all the foam out, this is a good time to glass in a flange, to give you something to reattach the top deck back onto. I bought 10 yards each of 1" and 2" width fiberglass cloth, along with a quart of West Systems epoxy, and a 2 gallon set of 2lb foam.





    Refoaming the board took 12 pours, a cup at a time, then I glassed the top deck back on, and did 3 more pours thru the 2" holes I cut into the top deck.



    Make sure both the board and the foam is at 80 degrees Farenheit, or your foam won't expand enough; you'll run out of foam, and the board will be too heavy.

    Once the sides are filled, I glassed the top deck back on, with 3 layers of fiberglass and epoxy. I meant to do 4 layers, and used a body grinder to grind back a taper 3" wide to fill. Unfortunately I didn't grind it deep enough, and 3 layers was all I could fit. It's plenty strong, but I wouldn't go any less than 3 layers.

    As you're pouring thru the holes, have the board tipped up at a 45deg angle. When the foam reaches the hole, throw a piece of duct tape over the hole, and move on to the next one. Wait a minimum of 20 min's between each pour, to give the foam time to set up.

    Let the foam set up overnight, and use a scraper to carve the foam back, and glass back in the holes in the deck.

    Attached Images Attached Images
    Last edited by delagem; 04-24-2011 at 09:16 PM.
    '58 Vincent Amanda Water Scooter, 0rpm, 0mph

    '84 SurfJet 236ss Freestyle, 5950rpm, 24.6 mph

    '91 Jetmate! SX-R 800,GroupK carbs,R&D 26cc head,R&D ProLok F/A, Coffman Rocket Pipe,Impros 13-20,76mm nozzle: 6630rpm and 38.1mph GPS

    '92 SL650/750, dry pipe,extended pump,trim,HotSeat Waterbox: 6320rpm, 50.1 mph

    '00 SLX,Tau Ceti F/A's,NuJet prop: 6670rpm, 63.1 mph

    '03 Octane, Watcon 2318 CDI

    '04 MSX140,Impros stage 2 Powertune 14/23,WetWolf,6deg wedge: 6750rpm, 60.5 mph

  4. #4
    PWCToday.com Is My Home Away From Home delagem's Avatar
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    Re: 1984 SurfJet!

    Don't use automotive Bondo on your board; it's made with corn starch and can absorb water. Instead, if you need filler, buy some West Systems 407 Low Density Fairing Filler.

    I painted my board with Dupont Chroma Systems paint. Base coat, then clear coat. The Ducati yellow I had turned out to be a nearly perfect match to the paint under the stickers, where it hadn't faded.



    Some form of traction is needed. I'm partial to Hydroturf. I went with the dual layer stuff they're selling. This isn't the production turf that they were having problems with, this is the custom order stuff that hasn't had problems delaminating.

    Attached Images Attached Images
    Last edited by delagem; 04-24-2011 at 09:23 PM.
    '58 Vincent Amanda Water Scooter, 0rpm, 0mph

    '84 SurfJet 236ss Freestyle, 5950rpm, 24.6 mph

    '91 Jetmate! SX-R 800,GroupK carbs,R&D 26cc head,R&D ProLok F/A, Coffman Rocket Pipe,Impros 13-20,76mm nozzle: 6630rpm and 38.1mph GPS

    '92 SL650/750, dry pipe,extended pump,trim,HotSeat Waterbox: 6320rpm, 50.1 mph

    '00 SLX,Tau Ceti F/A's,NuJet prop: 6670rpm, 63.1 mph

    '03 Octane, Watcon 2318 CDI

    '04 MSX140,Impros stage 2 Powertune 14/23,WetWolf,6deg wedge: 6750rpm, 60.5 mph

  5. #5
    PWCToday Regular Jay R.'s Avatar
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    Re: 1984 SurfJet!

    Great thread, nice write up!
    Yamaha Family Fleet:
    1999 XL700 L
    1996 WaveBlaster 2 760 (x2)
    1995 Waveraider 700 DLX

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  6. #6
    PWCToday.com Is My Home Away From Home delagem's Avatar
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    Re: 1984 SurfJet!

    I took some basic measurements before tearing down the motor. Was I surprised to find the motor had a backwards squish! The piston dome has a 7deg curve, yet the head is absolutely flat; this causes a squish that's 2mm immediately adjacent to the combustion chamber, and over 3mm at the outer rim of the head/cylinder. This is going to take some machining to fix.



    We used a Comparator to determine the angle of the crown on the piston. It's 7 degrees. Then, we mounted the head to the cylinder, and scribed the ring of the cylinder onto the head.



    We made up a jig to hold the cylinder in a lathe. The small aluminum button is the same bore as the cylinder. It is used to ensure the head is perfectly centered in the lathe. Then, we machined a 7 deg angle on the head.





    After the head was cut, we reassembled the motor, and rechecked the squish. It was a 2.7mm, way too big. There are better ways of determining squish based on Mean Squish Velocity (MSV); unfortunately I'm not that smart. So I pulled out my old copy of Bell's Two Stroke Performance Tuning, and looked to his table on squish. He suggests a gap of approximately .8 to .9mm for a cylinder of this diameter. Due to the design of this head, milling the head will not close up squish at all. Further, the design of this motor has the cylinder cast as part of the upper case, so there's no base gasket to leave out. Instead, the cylinder must be decked by 1.8mm. That's a huge cut!
    Attached Images Attached Images
    Last edited by delagem; 04-24-2011 at 09:35 PM.
    '58 Vincent Amanda Water Scooter, 0rpm, 0mph

    '84 SurfJet 236ss Freestyle, 5950rpm, 24.6 mph

    '91 Jetmate! SX-R 800,GroupK carbs,R&D 26cc head,R&D ProLok F/A, Coffman Rocket Pipe,Impros 13-20,76mm nozzle: 6630rpm and 38.1mph GPS

    '92 SL650/750, dry pipe,extended pump,trim,HotSeat Waterbox: 6320rpm, 50.1 mph

    '00 SLX,Tau Ceti F/A's,NuJet prop: 6670rpm, 63.1 mph

    '03 Octane, Watcon 2318 CDI

    '04 MSX140,Impros stage 2 Powertune 14/23,WetWolf,6deg wedge: 6750rpm, 60.5 mph

  7. #7
    PWCToday.com Is My Home Away From Home delagem's Avatar
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    Re: 1984 SurfJet!

    This sketch should make it a bit more clear what we're trying to fix with the machining of the head and cylinder. There's a huge gap around the outside edge of the top of the piston, where it nears the head. This excess fuel isn't burned during combustion, and instead goes out the tailpipe. It's one of 4 reasons the 255cc SurfJet only makes 16 horsepower.

    Attached Images Attached Images
    Last edited by delagem; 04-24-2011 at 10:00 PM.
    '58 Vincent Amanda Water Scooter, 0rpm, 0mph

    '84 SurfJet 236ss Freestyle, 5950rpm, 24.6 mph

    '91 Jetmate! SX-R 800,GroupK carbs,R&D 26cc head,R&D ProLok F/A, Coffman Rocket Pipe,Impros 13-20,76mm nozzle: 6630rpm and 38.1mph GPS

    '92 SL650/750, dry pipe,extended pump,trim,HotSeat Waterbox: 6320rpm, 50.1 mph

    '00 SLX,Tau Ceti F/A's,NuJet prop: 6670rpm, 63.1 mph

    '03 Octane, Watcon 2318 CDI

    '04 MSX140,Impros stage 2 Powertune 14/23,WetWolf,6deg wedge: 6750rpm, 60.5 mph

  8. #8
    PWCToday.com Is My Home Away From Home delagem's Avatar
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    Re: 1984 SurfJet!

    In making these modifications we have 3 concerns;

    1. We want to match the crown of the piston, and machine this onto the head, to create a squish band

    2. We want to close up this squish band, to improve our thermodynamic efficiency

    3. We need to calculate our compression ratio, to be sure our motor can be operated safely on the type of fuel we wish to run.

    My goal here was to run this machine on 91 Octane pump gas. According to this chart, we need to stay below about 12.5 to 1 to stay safe on 91.

    Attached Images Attached Images
    Last edited by delagem; 04-24-2011 at 10:03 PM.
    '58 Vincent Amanda Water Scooter, 0rpm, 0mph

    '84 SurfJet 236ss Freestyle, 5950rpm, 24.6 mph

    '91 Jetmate! SX-R 800,GroupK carbs,R&D 26cc head,R&D ProLok F/A, Coffman Rocket Pipe,Impros 13-20,76mm nozzle: 6630rpm and 38.1mph GPS

    '92 SL650/750, dry pipe,extended pump,trim,HotSeat Waterbox: 6320rpm, 50.1 mph

    '00 SLX,Tau Ceti F/A's,NuJet prop: 6670rpm, 63.1 mph

    '03 Octane, Watcon 2318 CDI

    '04 MSX140,Impros stage 2 Powertune 14/23,WetWolf,6deg wedge: 6750rpm, 60.5 mph

  9. #9
    PWCToday.com Is My Home Away From Home delagem's Avatar
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    Re: 1984 SurfJet!

    The formula for determining compression ratio is:

    The equation for Compression is:

    Cr = (V1 + V2) / V1

    Where V1 is the volume of the head and squish combined
    V2 is the volume of the swept piston (127.5cc for a stock SurfJet)

    We need to measure the cc's of the stock SurfJet head, and the modified head. The stock head worked out to 9.0cc's. The Delagem modified head worked out to 9.6cc's. The increase in combustion chamber volume is offset by the decrease in the volume of the squish band, raising the compression ratio.

    THEORETICAL CALC’S

    A stock Surfjet:

    Cr = (9.0 + 5.1) + 127.5/ 9.0 + 5.1

    Cr = 10.0

    A modded head on a 1st over bore:

    Cr = (9.6 + 2.3) + 128.4/9.6 + 2.3

    Cr = 11.79

    There are errors in doing theoretical calculations of Compression Ratios. They don't take into account the crown of the piston, for example. So, as a double-check, I took off the top piston ring, and put an O ring in its place. Then, I reassembled the engine. I put the piston at TDC and packed the groove between the cylinder and piston with grease, and reinstalled the head. Then, I used a burette to determine the exact volume. It came out to 11.7, or 2cc's less than the theoretical calculation.

    This gave me an actual Compression Ratio of:

    Cr = 11.7 + 128.4/ 11.7

    Cr = 11.97



    Attached Images Attached Images
    Last edited by delagem; 04-24-2011 at 10:24 PM.
    '58 Vincent Amanda Water Scooter, 0rpm, 0mph

    '84 SurfJet 236ss Freestyle, 5950rpm, 24.6 mph

    '91 Jetmate! SX-R 800,GroupK carbs,R&D 26cc head,R&D ProLok F/A, Coffman Rocket Pipe,Impros 13-20,76mm nozzle: 6630rpm and 38.1mph GPS

    '92 SL650/750, dry pipe,extended pump,trim,HotSeat Waterbox: 6320rpm, 50.1 mph

    '00 SLX,Tau Ceti F/A's,NuJet prop: 6670rpm, 63.1 mph

    '03 Octane, Watcon 2318 CDI

    '04 MSX140,Impros stage 2 Powertune 14/23,WetWolf,6deg wedge: 6750rpm, 60.5 mph

  10. #10
    PWCToday Regular Jay R.'s Avatar
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    Re: 1984 SurfJet!

    Do you have a copy of the "two stroke tuners guide" by Gordon Jennings? I have a PDF copy if not. great reading, probably in line with your bells.
    Yamaha Family Fleet:
    1999 XL700 L
    1996 WaveBlaster 2 760 (x2)
    1995 Waveraider 700 DLX

    1995 Seadoo GTX

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