650 to 701 conversion

[Freestyleriverrat]

I wanted to help build up the tech section so I though I would try and write up a 650 to 701 conversion thread. I have been learning allot over the last few months from workiing on my ski. I'll start out by illustrating stuff about cases. I will try to be as clear and comprehensive as possible. if you have any info to add please feel welcome and I'll include it within the text of that particular section.

 

[Freestyleriverrat]

How to Convert a Yamaha 650cc to 701cc​

This thread is aimed to answer questions for individuals with an existing 650 motor that want to drop in a 701. I had groupK ported 650 with a protect pipe, dual 38’s, head producing 190psi, lightened flywheel and an MSD enhancer that ran well up top but did not have that low end snap compared to even a stock 701. Here are some considerations to look into when swaping your motor to a 701.

Cases

All 650 (6M6), early 701 (61X) and newer 701’s (62T) have the same bottom half of the case and utilize the same bed plates for mounting to the hull. The difference in cases lies with the top half of the case and reed design.

The 650 (6M6) cases work well in on a stock motor but they are often the bottleneck on power. Generally speaking a motor is a air pump, so the more air you can feed into the motor the more power you can potentially produce. The 6M6 cases will work for a 701 conversion if you clearance the top case to accept a larger cylinder. If you have power in mind this is not a desirable option b/c you will produce less power than a stock 701 due to the smaller intake track and corresponding reed cage.

The early 701 (61X) looks allot like the 6M6 cases but don’t be fooled. If you get a 61x motor expect to be purchasing a intake manifold and reed cages along with the cases. Although they are similar in appearance the 61X reed cages are slightly larger in order to supply the larger cylinders. Although this set up works quite well and will produce more power than the 6M6, limitations will soon be apparent if you begin modify the motor for more power. The same bottleneck that plagued the 6M6 will arise b/c the change in design was not great enough to over come the inherent problem of reed size. Likewise there are not as many aftermarket options for reeds, reed petals and carburetion systems so that may be a limiting factor to consider when building a 61X motor.

Yamaha finally addressed the inherent design problem with the 6M6 and 61X’s by making the 62T cases. The reason for the change was to allow the cases to accommodate the larger reed valve which was the whole point for the 61X changes as well. This is the most desirable set of cases for this reason. Not only do they perform better in stock form, but the aftermarket has many parts to optimize air flow such as reed stuffers, reed spacers, higher flowing intake manifolds, reed cages, different tension reed petals and complete carburetion systems.

** See pic below for a comparison between the 6M6, 61X and 62t reed cages
Pic #1: 6m6 bottom, 61x middle, 62t top
Pic #2: 61x bottom, 62t top
Pic #3: 61x bottom, 6m6 top

 

[SkiDaddy]

So far so good!

 

[Shonuff]

Nice writeup thus far.

Would a 760 have better low hit or is it more of a race motor?

 

[onesojourner]

this good info for a yamaha noob like me. keep it coming.

 

[MADMAT]

Great thread!!! I think my friend is about to do this.

 

[sflsurfrider]

real nicce so far. it seems more like a write-up on the differences between the 3 case styles. maybe thats what it should be then you can put the 61x/6m6 conversion in addition. perhaps some pics of all three case styles side by side as you did their respective reed cages.

 

[cookerq62]

Differences between outside sleeve diameters and what bores the different cases will accept or need to be bored to accept the bigger cylinders would be some useful info.

 

[T-bone]

does anyone run a duel carb set up on their 61x, i was wondering if it was worth the hassle, i have all the stuff to go to duel 46 buckshots on my blaster.

 

[Freestyleriverrat]

Differences between outside sleeve diameters and what bores the different cases will accept or need to be bored to accept the bigger cylinders would be some useful info.

I'll see if I can find those specs. If anyone has any pics of the different cases pm me. All I have is the 6m6 right now and the 62T, but it is all buttoned up.

 

[Freestyleriverrat]

How to Convert a Yamaha 650cc to 701cc...........continued​

Electronics Compatablity

Simple rule of thumb........run your current setup. This is a plus if you already have a 6M6 b/c the 6M6 and 61X flywheels are lighter from the factory due to their construction. If you have it lightened even further that is just a little added bonus. There are a few discrepencies involving the factory rev limiter setting and the temperature sensor but they both have easy solutions......just eliminate or modify them.

**To find out how to modify the factory rev limiter: http://www.x-h2o.com/threads/496

The only reason to remove the factory temp/overheat sensor is if you are running an aftermarket head like I am. If you are using a factory head equipped to mount the sensor there is no need to eliminate it. All you need to do to eliminate this is cut it off about 1 in above the electrical box and fill in the end with silicone or equivilent for a water tight seal.

Starter and bendix gear are all the same so you could go from a 6m6 to the set up below just by plug and play.

 

[Freestyleriverrat]

more pics........62T cases, 61X cylinder with 6M6 electronics mounted (shown w/ lightened 6m6 flywheel)

 

[DaUpJetSkier]

Well I guess its time to bring this thread back from the dead with a ?, I just want to get a clarification. So there is no modding necessary if you run 62T top and bottom cases, a 61x OR 62T Cylinder, same ? for heads, and any electrics if they 6M6 has the rev limiter fixed. I currently have a 650 and am starting to look for parts for a 701 build up.

 

[Freestyleriverrat]

Sorry man I have been busy building my ski.......I'm have some good info on the cylinders I will compile tonight and post a cylinder section.

How to Convert a Yamaha 650cc to 701cc...........continued

Cylinder Head Compatablity

In short a 701 cylinder will bolt up to either a 62T or 61x set of cases. The 6M6 cases will fit a 701 cylinder if they are clearanced. A 701 or 760 head will not fit the 650 b/c of bore diameter and vise versa. For that same reason the 701 head will not fit the 760 cylinder, the cylinders are different. However, if you are getting an aftermarket head that has removable domes all you would have to do is get the corrosponding domes for the specific application. For example I can run my ADA head on a 701 motor with the right domes. If I convert to a bb 760 or a lamey cylinder w/ kawi flat top pistons all I need to do is order the domes for that bore and piston type. I have not seen domes to run a 650 cylinder so the best option there is hold off on aftermarket heads until you get a 701. This is not a huge draw back b/c a stock head will work just fine for you and I have seen them for as little as $5 bucks

 

[Freestyleriverrat]

So there is no modding necessary if you run 62T top and bottom cases, a 61x OR 62T Cylinder, same ? for heads, and any electrics if they 6M6 has the rev limiter fixed. I currently have a 650 and am starting to look for parts for a 701 build up.

The 701 cylinder (61x or 62T) will bolt up to either set of 701 cases w/o modifications, b/c what you are doing is assembling a 701 motor (cases and cylinder). Yes, the 6M6 rev limiter is fixed but it can be disabled all togather (see above link for that modification). The only reason the motor would over rev is if it was out of the water, when the pump is loaded you won't have that problem.

 

[Freestyleriverrat]

What you need to know about the differences between your cylinder of choice

650 vs the 701's

In short, the 6m6 cylinder has different ports than the 61x or 62t therefore you will have to factor in a different exhaust manifold or complete system into your build budget. Often times if you buy a complete motor the factory exhaust will be included or you can by this seperatly for very cheap.

61x vs 62T

In essence, the 61x and 62t have the same cylinders, however, the height of the port on the cylinder castings are slightly different. In contrast to the 61x cylinder the 62T's exhaust ports are raised = decreasing port timing = decreased low end "snap". The main reason for the difference was because the 62T cylinder was primarily used on the Wave Raider, a craft that had high speed and high revs in mind. This goal is also evident in the flywheels. The 62T flywheel has the magnet all the way around the inside of the flywheel, increasing its weight which is more suited for top speed boats. The slightly lighter 61x flywheel increases the low end response and enabled the motor to rev up faster for that initial low end power. Because the cylinder was designed for the Raider application the exhauts manifold bolts had to be incresed from 8mm (61x) to 10mm (62T) to support the increased weight of the larger raider exhaust system.

64X Cylinder (760)

The 64X cylinder is also better known as the 760. This is pretty much identical to the 62T cylinder in respect to the port height, yet boasts a larger displacement cylinder sleeve for even more power............Yamaha is taking advantage of the old trick no replacement for displacement when they developed this cylinder to put in their sit down craft that need the extra poneys to compensate for increased weight. Yet b/c it is essentially a larger cc 62T cylinder, it has the same draw back when it comes to higher port timing and decreased low end grunt. Although aftermarket porting can help this, most flatwater freestyle guys still prefer the 61x, which can be modified w/ larger cc cylinders while retaining the lower port timing. The 62t (701) and the 64X (760) are still great motor b/c they produce strong predictable power which is ideal for surf conditions where you do not necessarily need the instant hit desired by the flatwater guys.

 

[S&Ssuperjets]

the 64X cylinder come on the 62t case . So will all 62t cases accept a 64X cylinder ? Or do you have to bore the case ?

 

[waxhead]

remember two that there are a few style of heads and you have to use the right head gasket with each one

 

[Freestyleriverrat]

the 64X cylinder come on the 62t case . So will all 62t cases accept a 64X cylinder ? Or do you have to bore the case ?

Just off the top of my head I would say you have to do some minor clearancing to get the larger bore to fit the cases, but it is not a difficult job and can be done with a dremel.

remember two that there are a few style of heads and you have to use the right head gasket with each one

Any time the bore changes you will need the correct parts whether it be a ADA head (domes and O-rings) or a factory head (6m6, 701, 760). But through proper planning of the build the assembly should go togather just like you were rebuilding a top end. Obviously the easiest way of doing the swap is getting a complete motor. No matter what route you take it is important to know what you have so when you go to order parts you can accuratly reference parts for your application.

 

[Mouthfulloflake]

Differences in 62t 701 vs 61x 701 cylinders.

the sleeves are the same in the 62t 701 raider cylinders, the same sleeves as ni a 61x 701, ive had 3 of these cylinders in my hands and they all had 61x sleeves,, the exhaust port window of the cylinder casting ITSELF was slightly higher, but the sleeve port opening is the exact same height as a 61x exh port.

check this thread to see what I mean.

http://www.x-h2o.com/threads/1924&highlight=port+height