Page 1 of 2 1 2 LastLast
Results 1 to 10 of 13
  1. #1

    701 big bore vs 760

    got a 701 (62T) that I want to turn into a 760.
    bad part is cylinders and head are fine so cant justify
    boring.
    Do I need to get big bore sleeves and press them in or
    can the stock 62t cylinder be bored?
    Is there any difference in port timing,size shape etc to merit
    use of a 760 cylinder vs a 701 one?
    Will I need to use a 760 head and head gasket?
    what is this about staggered compression on the 760s?


  2. #2
    mjh3ides's Avatar
    Join Date
    Jul 2007
    Location
    Jupiter, Florida
    Posts
    6,805
    +1
    2,023
    The 760 port timing is different...better top end where the 701 is snappier down low. Also, I've read the bolt pattern on the ex. manifold is different on the 760 jugs, so you'll probably need a 760 manifold if you go that route. Sorry, I don't have answers to your other questions. If no one else chimes in, try searching at xh20.com. There's tons of info on these engines over there. You'll also be able to find a good amount of info on Group K's site.

  3. #3
    Ive got a Riva red pipe off a 760 Im going to use
    I thought it was only the size of studs/bolts that was different not the pattern.

  4. #4
    Mpeavler's Avatar
    Join Date
    Dec 2005
    Location
    Anderson, Indiana
    Posts
    5,155
    +1
    170
    760 is not a top end power maker...it was actually designed for bottom end power and fuel mileage if there was / is a thing. That's why all the free ride folks use the 760...more CC is more bottom end power. The 760's in stock "timing" actually have a poor top end power delviery where the 701's are more of a top end motor. The rear cylinder has about 5psi less then the front in stock form Gary.

    Mike

  5. #5
    mjh3ides's Avatar
    Join Date
    Jul 2007
    Location
    Jupiter, Florida
    Posts
    6,805
    +1
    2,023
    Quote Originally Posted by 96Waveventure700 View Post
    Ive got a Riva red pipe off a 760 Im going to use
    I thought it was only the size of studs/bolts that was different not the pattern.
    Yeah, I think you're right...just went & looked that up again. I think I was also wrong about the port timing difference. It's the 61X 701's that have the shorter ex ports for better bottom end, not the 62T. Don't you hate when people give you bad info on forums.

  6. #6
    Mike have any idea why the rear cylinder has lower compression?Which cylinder is better to use,the 701 bored to 760 size or the 760 one?
    ]

  7. #7
    As weight and pump sizes increased so did so did the amount of load on the engine. Yamaha found that heavy skis with pumps that hook up well were causing additional heat buildup in the rear cylinders. The heat buildup was leading to oil wiping and seizures. To help combat the problem, Yamaha staggered the compression and installed larger main jets in the rear carbs. This isn't the optimum setup. Its more of a band aide. But I'm sure it reduced warranty service cost for yamaha quite a bit. Many people run their jetting and compression balanced when building these motors. For performance.

    Improve cooling and make sure carb jetting and timing are right and it should be just fine. The rear cylinder compression is reduced via a larger dome in the rear. An aftermarket head or having the head milled and the domes recut would rectify the situation. Don't just use any domes or let anyone cut them since there is a large difference from one to another. Kommander is supposed to have one of the best performing domes.

    The 62T 701 and 760 cylinder are the same casting. The exhaust manifold bolt holes are the same on both. The manifolds will also interchange with problem. The 61x 701 cylinder does have smaller bolt holes for the exhaust manifold. The exhaust outlets on the 61x cylinder are also SLIGHTLY different as well but not enought to matter in most cases.

    As far as boring the 62t 701 to take 760 pistons. Go for it. The exhaust port on the 760 is a few degrees higher than the 62t 701.the extra exhaust port time will increase overall power a little and it will also start to make that power at a little higher RPM. If you decide you wanted to replicate the 760 more closely, the port roofs could be raised to the 760 specs. Or you could raise it more in the center than the sides to make power delivery more linear. Exhaust port roofs that are arched deliver power more smoothly. Flat exhaust port roofs tend to deliver power more like a hammer.

    You could also fine the port maps for the norhwest 760/big bore sleeves and match your sleeves to that. Or you could just install a set at 84mm bore for a fun 760 the sleeves are "pre-ported" and I've been told the specs are very nice. The bottom of the sleeve is thicker so allows for larger pistons than a stock 760 sleeve as well. The casting woud need to be blended to the ports on the sleeve after they are installed.

    BTW, please don't try pressing sleeves in or out of your cylinder. It won't work and will destroy things. Place your cylinder in an oven at 450 degrees for 30-45 minutes then quickly remove the sleeves. They will slide right out from the top. Reverse to install new ones. Don't put the sleeves in the freezer before install. This will give you less time to adjust the sleeves when installing them. Room temp sleeves works great. After sleeves are installed, bolt the head on with an old head gasket and torque to spec. Put this back in the oven at 450 another 45 minutes. This helps to seat the sleeve and insure against having a sleeve seat after final assembly possibly causing a leak in your head gasket.

    Ok. Way too much typing on my cell phone. I'm done.

  8. #8
    Ok... one more thing to add.... I find that putting a cylinder in the oven on a cookie sheet right side up is nice. When the casting is hot enough it will drop down onto the cookie sheet as its weight pushes the sleeves out. Take the cyl out of the oven still on the cookie sheet and grab the old sleeves with a pot holder, pliars, whatever and pull them out.

    I also find that when installing the new sleeves, its nice to have a top case near by. I put the heated cylinder on the top case making it a lot easier to get the sleeves in and aligned properly.

    Focus on one sleeve at a time. Put the cylinder back in the oven to install the second sleeve. Put cylinder on the cookie sheet on its side to help prevent disturbing the already installed first sleeve.

  9. #9
    Every adventure comes to an end........ Not Today! wreckingball's Avatar
    Join Date
    Sep 2009
    Location
    San Diego, California, United States
    Posts
    1,347
    +1
    2
    Quote Originally Posted by ArtMaybee View Post
    As weight and pump sizes increased so did so did the amount of load on the engine. Yamaha found that heavy skis with pumps that hook up well were causing additional heat buildup in the rear cylinders. The heat buildup was leading to oil wiping and seizures. To help combat the problem, Yamaha staggered the compression and installed larger main jets in the rear carbs. This isn't the optimum setup. Its more of a band aide. But I'm sure it reduced warranty service cost for yamaha quite a bit. Many people run their jetting and compression balanced when building these motors. For performance.

    Improve cooling and make sure carb jetting and timing are right and it should be just fine. The rear cylinder compression is reduced via a larger dome in the rear. An aftermarket head or having the head milled and the domes recut would rectify the situation. Don't just use any domes or let anyone cut them since there is a large difference from one to another. Kommander is supposed to have one of the best performing domes.

    The 62T 701 and 760 cylinder are the same casting. The exhaust manifold bolt holes are the same on both. The manifolds will also interchange with problem. The 61x 701 cylinder does have smaller bolt holes for the exhaust manifold. The exhaust outlets on the 61x cylinder are also SLIGHTLY different as well but not enought to matter in most cases.

    As far as boring the 62t 701 to take 760 pistons. Go for it. The exhaust port on the 760 is a few degrees higher than the 62t 701.the extra exhaust port time will increase overall power a little and it will also start to make that power at a little higher RPM. If you decide you wanted to replicate the 760 more closely, the port roofs could be raised to the 760 specs. Or you could raise it more in the center than the sides to make power delivery more linear. Exhaust port roofs that are arched deliver power more smoothly. Flat exhaust port roofs tend to deliver power more like a hammer.

    You could also fine the port maps for the norhwest 760/big bore sleeves and match your sleeves to that. Or you could just install a set at 84mm bore for a fun 760 the sleeves are "pre-ported" and I've been told the specs are very nice. The bottom of the sleeve is thicker so allows for larger pistons than a stock 760 sleeve as well. The casting woud need to be blended to the ports on the sleeve after they are installed.

    BTW, please don't try pressing sleeves in or out of your cylinder. It won't work and will destroy things. Place your cylinder in an oven at 450 degrees for 30-45 minutes then quickly remove the sleeves. They will slide right out from the top. Reverse to install new ones. Don't put the sleeves in the freezer before install. This will give you less time to adjust the sleeves when installing them. Room temp sleeves works great. After sleeves are installed, bolt the head on with an old head gasket and torque to spec. Put this back in the oven at 450 another 45 minutes. This helps to seat the sleeve and insure against having a sleeve seat after final assembly possibly causing a leak in your head gasket.

    Ok. Way too much typing on my cell phone. I'm done.
    Quote Originally Posted by ArtMaybee View Post
    Ok... one more thing to add.... I find that putting a cylinder in the oven on a cookie sheet right side up is nice. When the casting is hot enough it will drop down onto the cookie sheet as its weight pushes the sleeves out. Take the cyl out of the oven still on the cookie sheet and grab the old sleeves with a pot holder, pliars, whatever and pull them out.

    I also find that when installing the new sleeves, its nice to have a top case near by. I put the heated cylinder on the top case making it a lot easier to get the sleeves in and aligned properly.

    Focus on one sleeve at a time. Put the cylinder back in the oven to install the second sleeve. Put cylinder on the cookie sheet on its side to help prevent disturbing the already installed first sleeve.
    Best phone typing I've ever seen! And I learned something too! Looks like you've only been on the Hulk for a few months, but you really should get on more. Great post!

  10. #10
    Quote Originally Posted by ArtMaybee View Post
    As weight and pump sizes increased so did so did the amount of load on the engine. Yamaha found that heavy skis with pumps that hook up well were causing additional heat buildup in the rear cylinders. The heat buildup was leading to oil wiping and seizures. To help combat the problem, Yamaha staggered the compression and installed larger main jets in the rear carbs. This isn't the optimum setup. Its more of a band aide. But I'm sure it reduced warranty service cost for yamaha quite a bit. Many people run their jetting and compression balanced when building these motors. For performance.

    Improve cooling and make sure carb jetting and timing are right and it should be just fine. The rear cylinder compression is reduced via a larger dome in the rear. An aftermarket head or having the head milled and the domes recut would rectify the situation. Don't just use any domes or let anyone cut them since there is a large difference from one to another. Kommander is supposed to have one of the best performing domes.

    The 62T 701 and 760 cylinder are the same casting. The exhaust manifold bolt holes are the same on both. The manifolds will also interchange with problem. The 61x 701 cylinder does have smaller bolt holes for the exhaust manifold. The exhaust outlets on the 61x cylinder are also SLIGHTLY different as well but not enought to matter in most cases.

    As far as boring the 62t 701 to take 760 pistons. Go for it. The exhaust port on the 760 is a few degrees higher than the 62t 701.the extra exhaust port time will increase overall power a little and it will also start to make that power at a little higher RPM. If you decide you wanted to replicate the 760 more closely, the port roofs could be raised to the 760 specs. Or you could raise it more in the center than the sides to make power delivery more linear. Exhaust port roofs that are arched deliver power more smoothly. Flat exhaust port roofs tend to deliver power more like a hammer.

    You could also fine the port maps for the norhwest 760/big bore sleeves and match your sleeves to that. Or you could just install a set at 84mm bore for a fun 760 the sleeves are "pre-ported" and I've been told the specs are very nice. The bottom of the sleeve is thicker so allows for larger pistons than a stock 760 sleeve as well. The casting woud need to be blended to the ports on the sleeve after they are installed.

    BTW, please don't try pressing sleeves in or out of your cylinder. It won't work and will destroy things. Place your cylinder in an oven at 450 degrees for 30-45 minutes then quickly remove the sleeves. They will slide right out from the top. Reverse to install new ones. Don't put the sleeves in the freezer before install. This will give you less time to adjust the sleeves when installing them. Room temp sleeves works great. After sleeves are installed, bolt the head on with an old head gasket and torque to spec. Put this back in the oven at 450 another 45 minutes. This helps to seat the sleeve and insure against having a sleeve seat after final assembly possibly causing a leak in your head gasket.

    Ok. Way too much typing on my cell phone. I'm done.
    thanks for such an intelligent and well thought out post(and I'll add painful too)

    how would you go about improving the cooling so it wont be a problem?

    If I use the 701 head and 760 headgasket wont the CR be a bit too high for midgrade gas?

Page 1 of 2 1 2 LastLast

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. 84.8 mph on my big bore GPR!
    By Pistonwash in forum 4-Tec Performance
    Replies: 41
    Last Post: 08-10-2008, 09:53 AM
  2. r/d stage 2 VS 1390 Big bore
    By alex29573 in forum Yamaha PWC Performance (2-stroke)
    Replies: 9
    Last Post: 04-19-2008, 02:29 AM
  3. Big Bore Vs 1300
    By CanadianGPR in forum Yamaha PWC Performance (2-stroke)
    Replies: 5
    Last Post: 05-28-2007, 08:40 PM
  4. 1600 & 1700 cc big bore kit
    By PAINKILLER in forum 4-Tec Performance
    Replies: 43
    Last Post: 03-09-2006, 06:53 PM
  5. Big bore 4 tec
    By 01xdime in forum 4-Tec Performance
    Replies: 10
    Last Post: 12-29-2005, 09:40 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •