Yamato Cooling

[reed28n]

Not enough Water

The most common overheating with the 102 or 302 is the lack of water. In General the motors are very forgiving as a stock motor to carb setting. You be at little lean without seizing the motor.

If you have ever looked off the transom of a pleasure boat under way you will notice that path the water takes as it passes the trailing edge of the transom. The water travels the path of a curve or wave.

Placing your motor and water pick up in the correct part of this curve will give you optimum depth and density of water to insure your prop forces sufficient water to the intake to cool your motor. Transom angle determines this location, or shimming your motor back or moving your motor forward.

The main issue for one driver switching from a 102 to a 302 is moving the water pick location closer to the trailing edge of the boat because the toers are different heights. As you cut your transom down you move your prop closer to the boat.

Density of the water is another concern. Your gearfoot and your prop and the bottom of your boat can alter the amount of slip or cavitation you produce in front of your water inlet. The more disturbance created the more air in the water the less volume of water to your powerhead. That being stated water condition can affect this phenomena places like Lock Haven will steam motors. Take a shim out.

Don't forget that when you add depth to your air traps at the back of your boat you can potentially pack more air under the bottom jacking your water pick up higher.... in summary 302's can be cooled at 1/2" height rule, but not everyone will have the same formula or combination to do it.
Scott

[sam]

Rich, I'm not sure you are connecting with the unique issues regarding the Yamatos and their prop thrust cooling system.

Al correctly pointed out what goes on ... it is not an issue for the original application in Japan where they get their primary use, so there is no issue for Yamato to address or resolve ... it is an issue outside Japan where they are used other than the manufacture intends. What happens outside of Japan is that they are run with props not made by Yamato, on boats not made by Yamato, higher on the transom and at significantly higher boat speed.

Running on a course (day) that has something funny going on like wind or current at an angle to the course or across a turn and then the spray angle from the prop tip to the water inlet becomes insufficient to cool the motor on a set up that normally works OK ... the problem is not always reproducible, can vary with driver's weight or even driving style. Some boat/prop/driver/set up combos are better than others for consistant cooling, some are not. Cooling the motor isn't the main objective, going faster than the next guy is - if there is some risk of motor failure, it is a risk most Yamato drivers are wiling to take to get to the finish line first.

I don't think there is a plug reading that will help - the mixture is good, the seizure is sudden due to sudden loss of cooling, I don't think they are seeing any loss of power until it is already too late to save the motor ... this is a big part of the problem.

[les]

102/302 cooling

then the Height restriction came in.
More testing.........
New boat design...still pumps and is now faster.
Dennis 21Z

Dennis,
After the height restriction... Did you have to lower the prop to stay legal? Or are you able to pump/cool at less than 1/2" deep?
Larry

[Rich Oliver]

Yamato Cooling

I would guess that if you could quantify the loss of power at or near seizure,it would be a huge difference between any gains in tweaking the gearfoot.Isn't cooling the motor the main objective?If you had the choice,Would you prefer 18mm or 14mm plugs?If cooling is a problem,and it seems like it is..What are you seeing when you look at the plugs?

[HYDRO21Z]

Another opinion

I have been running a 302 for the last 8 years.
The first 4 years spent testing and trying to get to the same height as the
102's.
After 2 cooked motors, we found the right combination to run with the 102's
then the Height restriction came in.
More testing.........
New boat design...still pumps and is now faster.
We are now close to the 102's in the straights, always faster through the turns.
I believe that the cooling issue is a result of a combo of things.....
1) Hull design ie transom angle -motor position.
Trying to put a 302 on a boat that was built for a 102 is part of the problem.
2) Props-- self explanitory.
3)Different water density, and conditions.
A)I raced in Jesup this weekend, and ran John Runne's 102 rig set up like he has run it all season, Water no rougher than anywhere else and I am 50#s heavier than John so the motor was planted, and it steamed.
B)Chris Johnson stuck his 102 there at the same setup he has run for years.
Two other yamatos overheated or stuck as well.----???????????
Goes to show that there are more reasons for overheating than gearfoot mods, height restrictions, and setup.
Oh by the way at Raleigh a few weeks ago in OSY400 I ran my 302 on my
RunneCraft at 5/8" below the bottom with a 5/16" tuck and it pumped water
strong, could have gone up to the 1/2" setting.
Dennis 21Z

[bill boyes]

Not if you know how to shape your gearbox.

The jury is still out if shaping the gear case improves cooling. It most certainly does not hurt performance. The most important thing to do is shape the skeg. In doing so there is not much a speed gain but in the improved boat handling characteristics. Do not try to do this yourself. Bob Gollor, Tj and Cronk all do a good job.

[Al Peffley]

Overheating Causes

I'll jump in here, since the overheating you see in multiple motors during a race has nothing to do with "shaping a foot" legally, or illegally. We run these force-fed, water-cooled motors much higher than they do in Japan for paramutual racing!

Yamato 102-202-302 overheating is usually caused by the motor being jacked up too high for the foot water intake hole to pick up enough water so that the motor cools properly. The overheating can be accelerated by too much cavitation around the opening, millfoil and other plant life residuals caught up in the intake, the wrong motor angle, propeller performance, solid objects in the water path (foreign objects or poor machine work inside the motor), spark plugs that are too high of a heat range, and a really lean engine carb setting! Some racers even pinch one of the water outlet tubes to make the engine run hotter (right on the edge of sticking.)

Many racers don't know how to check for this overheating problem. Wartinger told me many years ago that you can check your water flow by running a clear water line extension hose up next to the driver from the hottest hose on the motor. The clear extension hose is taped to the cockpit side up next to the driver's throttle hand (dumping out away from his/her hand on the sponson or runabout deck.) You watch the water while you are testing to see when it's steaming, and then adjust the height/kickout setup to stop the steaming. This is one reason why we are always running out of stock and OSY Yamato pistons -- too many stuck motors being run over the ragged edge for one or two races of competition...

Al Peffley
15-R/R-25

[mercguy]

Not if you know how to shape your gearbox.

how is the 302 foot shaped any different than an 80 or 102 foot...they are not! If "so-called" shaping was the solution/problem, than why do the other motors overheat also at times??? I also do not believe that the shaping allowed gives a great amount of advantage, as these motors are not running fast enough to benefit from increased "shaping". If you are so antimate about the Yamato gearfoot shaping, then why is it allowed on all the other "stock" outboards Ed, including the OMC, Merc, and Hot Rods (which you race!)??? Close the subject Ed and move on to the more important issues brought up..................like what I have asked before........WHAT IS ON THE SO AGENDA FOR 2007????????? You are running this topic into the ground and leaving others "hanging"............

[14-H]

There is no problem, ***.

Not if you know how to shape your gearbox.

There is no problem, that's the problem.

[Rich Oliver]

Whats the problem with Yamato cooling?I'am just getting into this with a new 302...after 15 years of development,what is the problem?I Watching the race at Millville during the fall meet this month, I noticed a trail of steam right behind the water flex hose area of the engines.I did think that was odd.
Rich