Yamato 302 cooling

[Trihedral_1]

Here is Tech Tip # 305-a:

For an existing or new 302 setup that could use some more water to the motor:

Instead of just adjusting the motor up & down, start moving the motor back by placing 1/4inch shims on the back of the transom. The further back you go, the better cooling you'll get. This can be a tricky adjustment, because as you move the motor back, the prop shaft depth will drop due to the boats transom angle. Compensate for this unwanted height change by placing shims on top of the transom (like you're raising the motor). Measure the shaft height after every shim and adjust. Also take note of the distance from the back of the boat (tunnel) to the front tip of the lower unit so if you change your shaft angle it can also be compensated for. This will work for any Yamato, and is a much better performance option than simply lowering the motor. It also provides for more propeller options.


Switching from a 102 or a 102 designed boat to a 302:

The goal here is to get your 302 lower unit and water pickup where the 102 lower unit and water pickup was, and have some extra room to adjust.

First set up your 102 like your racing.
Measure the prop shaft depth and shaft angle.
Use a 4' level on the bottom and measure the distance between the back of the boat (tunnel) to the front tip of the lower unit.

Now, cut the transom down to 302 height and prepare some nice 1/16" & 1/32" shims for the top of the transom, and some 1/4" shims for the back of the transom. (I can't honestly remember the exact amount you need to lower the transom -maybe someone can post that dimension).

Once the transom has been cut to accommodate the tower height, put on the 302 and start shimming until you reach your 102 setup, especially the measurement from back of the boat to the lower unit. If you run out of threads on the motor clamps, oops, at least it's closer, (or, give your friend the woodworker a call). Also, if you're building a new hull for a 302 (especially an OSY), remember to put the transom where you really need it for best performance.

Always keep the boat bottom flat and lower the motor when you try a new prop.


Jimi O (305-R)

[Kev43V]

Great post!

[PRO-MOTIONRACING]

"(I can't honestly remember the exact amount you need to lower the transom -maybe someone can post that dimension)."

I have done this many times it is 1 1/8"

[ZUL8TR]

Motor setup

Great advice. If height restrictions in CSH were not an issue this would be ideal for additional cooling,speed, handeling, etc.

Note that with the APBA CSH depth restriction of the back end of the prop shaft set at 3/4" min below the lowest bottom planing surface the further back the engine is shimmed the deeper the end of the prop shaft will be even if it is set to the 3/4" rule minimum once shimmed back and up as you explain. This is because the minimum angle of attack of the hydro relative to the water surface is set by the angle created by the afterplane length and the depth of the sponson at its rear planing surface. Therefore while moving the engine back provides better water pickup for cooling the greater the prop shaft end will be in the water. Plus the further back the greater the water rise is (above the level still water surface) from the bottom planing surface as it is releaved from below the bottom at a greater pressure than artmospheric and advances rearward.

This prop shaft depth increase effect can be somewhat reduced by kicking the engine out to raise the prop shaft end up but at the expense of greater bow lift.

Any adjustment is a compromise in this case of: speed, handeling and cooling and in the final analysis testing is required and then the real test is race conditions and further adjustment.

I use to do this in 25ssh (early 22ci and no cooling problem) and Y80 20ssh (possible cooling problem) before there were height restrictions in these classes and success was achieved in speed. performance, acceleration, cooling.

[Islandmon]

Great post Jimi, thanks for sharing.

Sam,

[propnuts]

20SS height

Any adjustment is a compromise in this case of: speed, handeling and cooling and in the final analysis testing is required and then the real test is race conditions and further adjustment.

While I'm as much in favor of testing as the next guy, I still favor lowering the height in 20SS to 3/4". Some of you say this would give an advantage to my 302, I'll take your word for it. Others say it will screw up my prop selection, so be it. While I happen to have (or did) the time and money to go testing and purchase the temperature guage needed to find out if my setup is cooking my motor, many people don't. I hate it when someone asks the height in 20SS and I have to say "it's 1/2 inch BUT you may burn up your motor if you try to run there" The reason I am in favor of the change is to give the noob/novice a chance to run at a setup roughly the same as other people's and not risk seizing up a motor.

[blueskyracer]

While I'm as much in favor of testing as the next guy, I still favor lowering the height in 20SS to 3/4". Some of you say this would give an advantage to my 302, I'll take your word for it. Others say it will screw up my prop selection, so be it. While I happen to have (or did) the time and money to go testing and purchase the temperature guage needed to find out if my setup is cooking my motor, many people don't. I hate it when someone asks the height in 20SS and I have to say "it's 1/2 inch BUT you may burn up your motor if you try to run there" The reason I am in favor of the change is to give the noob/novice a chance to run at a setup roughly the same as other people's and not risk seizing up a motor.

I guess I am a lazy racer but I have better things to do at a race than switch heights all the time. I always run 3/4 for both classes. But I must add I still have fun.

[glen wesanko]

Great post Jimi, I wish there was more practical information on HR from the more experienced racers.It's all about the racing really.That's the biggest kick and the bottom line.It really does'nt matter if the front runners are doing 66 67 or 68 mph.What would be fun is if most of the field was doing the same, making a better drivers race instead of a parade! I found that spending $75 on a cyl head temp guage will provide a certain amount of "peace of mind" when testing as an ocassional glance at the guage will keep you informed just how hot you are getting.If anyone else want's to chime in with more helpfull tips for us "mid fielders" I'm sure it would be equally well received.Is anyone else working their props ? I picked up a nice big old anvill and have been pounding on an few old wheels hoping to learn something once I get out and do some testing ? How about lead location in a hydro ? Should it be at the transom or is it better to spread it around a bit ? I'm running a 102,what rpm should I be looking for at speed ? How about ign timing ? What is the concensus on best advance spec ? Questions ...questions...questions flooding the minds of "mid fielders" during these long dark winter nights ! How am I going to get that elusive 1 1/2 mph without just throwing darts ie; dollars at the board.Thank's in advance JG Wesanko 36CW 2009 APBA High Points Sectional Winner Canada West : Pro Hydro,Mod Hydro,Stock Hydro,Stock Runabout.

[ZUL8TR]

engine height

While I'm as much in favor of testing as the next guy, I still favor lowering the height in 20SS to 3/4". Some of you say this would give an advantage to my 302, I'll take your word for it. Others say it will screw up my prop selection, so be it. While I happen to have (or did) the time and money to go testing and purchase the temperature guage needed to find out if my setup is cooking my motor, many people don't. I hate it when someone asks the height in 20SS and I have to say "it's 1/2 inch BUT you may burn up your motor if you try to run there" The reason I am in favor of the change is to give the noob/novice a chance to run at a setup roughly the same as other people's and not risk seizing up a motor.

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Although the original tread was about the 302 and my response while generic was essentially directed to that engine but as you suggest if the 20ssh height was lowered to match the CSH it should be considered by SORC and drivers to increase to 3/4" but that issue is for another thread.

[Trihedral_1]

....... I'm running a 102,what rpm should I be looking for at speed ? How about ign timing ? What is the concensus on best advance spec ? Questions ...questions...questions flooding the minds of "mid fielders" during these long dark winter nights ! How am I going to get that elusive 1 1/2 mph without just throwing darts ie; dollars at the board.Thank's in advance JG Wesanko 36CW 2009 APBA High Points Sectional Winner Canada West : Pro Hydro,Mod Hydro,Stock Hydro,Stock Runabout.

I run a 102 at 225 btdc, point gap .016-.018, plug gap .020, NGK 9 or 10 plug & look for 7100 RPM.

Here are the more official guys for Yamato info & parts & specs. They should have a copy of the original manuals that contain much more info.

Tom Johnston (517-451-9120 tjohnston@ini.net)
Ric Montoya/RPM Marine (206-283-4773 ricstr4@gmail.com)

Jimi O. (305-R)

PS: If the motor is running well, the best way to pick up a chunk of speed is usually to try different props.

[ZUL8TR]

engine specs

[QUOTE=Trihedral_1;149129]I run a 102 at 225 btdc, point gap .016-.018, plug gap .020, NGK 9 or 10 plug & look for 7100 RPM...................

..............................................

Jimi O. (305-R)

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Per the 102 Owners manual on the Ric Montoya RPM marine site the point setting is 0.012" - 0.016". How come you are at the top of the spec and beyond for the point gap? I have a Y80 and Tom Cronk set the ignition for both cylinderes at 0.220" btdc with top cylindere set of points at 0.012" and bottom cylindere came out a little wider to get the 0.220" btdc firing and NGK-AG9 18mm plugs at 0.030". The ignition point range for this engine is 0.012" - 0.016" per my service manual and Tom selected the lower spec. opening for the point gap. All I can surmise is that 0.012" point setting provides additional dwell time for the spark but it would require more gap maintenance since as the rubbing block wears the gap decreases. Note he also selected a wider plug gap than the 0.016" manual setting.

Your thoughts appreciated.

[Trihedral_1]

[QUOTE=ZUL8TR;149134]

I run a 102 at 225 btdc, point gap .016-.018, plug gap .020, NGK 9 or 10 plug & look for 7100 RPM...................

..............................................

Jimi O. (305-R)

-------------------------------------------------------
Per the 102 Owners manual on the Ric Montoya RPM marine site the point setting is 0.012" - 0.016". How come you are at the top of the spec and beyond for the point gap? I have a Y80 and Tom Cronk set the ignition for both cylinderes at 0.220" btdc with top cylindere set of points at 0.012" and bottom cylindere came out a little wider to get the 0.220" btdc firing and NGK-AG9 18mm plugs at 0.030". The ignition point range for this engine is 0.012" - 0.016" per my service manual and Tom selected the lower spec. opening for the point gap. All I can surmise is that 0.012" point setting provides additional dwell time for the spark but it would require more gap maintenance since as the rubbing block wears the gap decreases. Note he also selected a wider plug gap than the 0.016" manual setting.

Your thoughts appreciated.

Hmmmm. When I got my first 102 (in 1988) I asked Ric about set up, he said .016-.018, I wrote it down, and that's what I've always run.

As for your 80, my manual says timing between 180-200 & plug gap of .020. I know both these guys know Yamato motors top to bottom, so maybe there's something to it.

Maybe we should all read our manuals, or at least get a chuckle out of it.

Jimi O.

[Team B&H]

We spent considerable time and effort on the 302 to get it to cool at least marginally for 3 laps back when the propshaft could be level with the bottom. Without giving up everything we learned, 2 things are very important. Use a temperature gauge until you feel comfortable and safe without one. We got to the point where we were safe finishing a heat with a spark plug temp of 417 and immediately dropping off plane to refill the motor with water and if the temp got to 420, we would scuff a piston. But scuffing a new piston isn't all bad if your driver is competent enough to shut it off immediately when it starts to feel a bit flat. You can clean up the cylinder wall and sand the piston in the scuffed area and put it all back together. The sanded piston will be better than a new one because it is slightly smaller in the sanded area and won't scuff as easily as before.

But the most significant thing with a 302 is that the exhaust cover and the engine block MUST be flat and seal well. Most 302 exhaust covers are far from flat on the gasket surfaces as they come out of the box. If not too bad, you can lap it flat with a piece of 80 wet or dry paper on a flat surface. If really bad, you might need a trip to the Bridgeport to mill it flat. Even a slight exhaust leak here will pressurize the water jacket area and cut off the cooling water when the pressure drops to a minimum when you get going fast. Don't forget to check the block surface when you have the exhaust cover off. This also applies to 102 and 80 motors but they generally don't have the issue here that 302s do. We've had probably 8 or 9 302 motors and I'd only say that 1 or 2 were OK in this area.

[Islandmon]

Team B&H, for those of us who are less experienced this is the kind of knowledge that is really appreciated . At the risk of hijacking the original thread I was wondering if you had any basic rules of thumb as to when to replace rings on a 302. I understand that ring replacement is relative to running time, motor condition and a list of other factors. That said is there a point based on run time where you would think about changing rings.

Thx,

Sam

[blueskyracer]

I must say this is a very helpful thread. Where does someone get a temp gauge and where does the sender unit get located on the engine?

I also would like to know when a set of rings should be replaced? Is it based on time on motor or compression or something else?