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Triple Threat 21 Feb 2024 23:15 #128131

I am posting for my friend, Yanni Makolovitch, who has limited English comprehension.
He asked that all this information be dumbed down for him.
Thanks in advance.
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Triple Threat 21 Feb 2024 20:56 #128130

I always liked lotsa oil and fat jetting too.  Spark plugs are cheap and seldom have fouling issues with modern CD ignitions due to their very fast rise time.

Over the years I have noticed a surprising number of those three bangers up for sale on CL and FBMP with a "one cylinder has low compression" statement in the description.  Seems like I remember vintage 4 cylinder Mercury Thunderbolts with overheating issues with one cylinder as well.

Will do on the KX-125 cylinder and probably a motor too, just for yucks.

Cheers, keep up the exceptional work!

M
1957 FC Rocket -'58 Evinrude Lark 35
1958 FC Hawk 1-'59 Evinrude Lark 35 (and J-55)
1960 Starcraft 12' open boat-'76 Evinrude 25
1965 era McCorvey 3-point hydroplane-'52 Mercury KG-7H
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Last edit: by Merky Johnrude.

Triple Threat 21 Feb 2024 15:42 #128129

John,
Please do bring a cylinder for show and tell!
OMC had a bunch of cooling mods they released as service bulletins for these engines.
None had been done to this engine, that may be why it had so much cylinder wear.
It's surprising sometimes what difference a small change can make when it comes to heat.
The bridge on these looks wide enough to survive a good bit of heat, but I can see how any overheating from any issue, water cooling not right, jetting not right, oil mix not right, all can heat things up quick.
The later oval port motors had cooling issues that were, once more, addressed in service bulletins, the cooling ports were modified, and the jetting was upped in the center cylinder. 
From what I have read they were all over the place over the years on the jetting, I have always been inclined to jet as rich as I can get away with and run more oil than most and I will continue that with this engine.   
“Keep thy shop and thy shop will keep thee”
- Poor Richard’s Almanack, 1737

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Last edit: by Locomotion.

Triple Threat 21 Feb 2024 05:13 #128128

Beautiful motor. 

What a work of art!  My understanding is that bridged exhaust ports are more prone to heating up, expanding into the cylinder and interfering with the piston rings, Especially in air cooled engines. This bridge distortion often times caused the rings to stick if allowed to be too thin.  But they are certainly a key to long ring life if properly relieved.

Also on the plus side they allow for a considerably wider exhaust port.  Konig racing outboards used a partially bridged exhaust port.  It's bridge probably protruded only about 1/3 the way down from the top of the port and was slightly beveled as well as tapered to help keep the piston ring "happy."  My Kawasaki cylinders actually have five exhaust ports.  The two section main exhaust port is configured with a wider than normal bridge to dissipate heat, the other two pairs of ports lie on each side of the main port and contain rotating valves that change from closed to open to maximize the engines' torque at different RPM's. On top of all that, the main exhaust port is height adjustable (while running). Quite an interesting set up. The engineers who developed those 125cc two stroke  MX bikes were wizards in their own rights.  I'll try to remember to bring a cylinder to Arrowhead.  May also toss one of the motors in the van.

Keep up the great work and thanks for the pictures!

M
1957 FC Rocket -'58 Evinrude Lark 35
1958 FC Hawk 1-'59 Evinrude Lark 35 (and J-55)
1960 Starcraft 12' open boat-'76 Evinrude 25
1965 era McCorvey 3-point hydroplane-'52 Mercury KG-7H
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Triple Threat 20 Feb 2024 21:57 #128124

The ports are actually pretty large in the block before they dump into the tuner which is pretty small.
These early 56 cubic inch motors have bridgeport exhaust ports, they changed that in 1994 to single oval ports, why? I don’t know, I also don’t know if the 49 cubic inch triples had bridgeport exhaust ports. 
I had a few discussions with Joe when I was building the first crossbred 50 to 35, he said he had not really had to get into exhaust design, racing mostly “stock” engine classes.





“Keep thy shop and thy shop will keep thee”
- Poor Richard’s Almanack, 1737

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Last edit: by Locomotion.

Triple Threat 20 Feb 2024 05:30 #128117

That is a good question.  I have no real idea.  

It looks like (from a quick look through the Marine Engine parts lists) that my 76 55hp looper and the three bangers of that time were using pretty much the same main jets (53D and later 54D).  Then I checked the triple looper from 1990 and it was spec'd as a 52D.  Not much of a real difference here but we don't have a way to figure into all this the contribution from the low speed circuit which may have been "adjusted' over time by the design engineers.  All this came about as I was initially wondering if all three carbs on that three cylinder mighty monster used the same main jet and apparently they do.

So, back to the original question, it may be that on the three cylinder motors, the length of the exhaust tracks leading away from the cylinder isn't all that critical, relatively speaking.  One other factor playing a role in improving the cylinder scavenging via the exhaust ports is the area of the header leading into the tuned section.  Since apparently all this "expansion chamber" tuning is predicated on sound waves, the tighter the better with a smooth transition from the exhaust port to the pipe for presenting a strong "signal" at the exhaust port helping to improve blocking of the incoming fresh fuel charge from short circuiting out the open exhaust port when the intake and exhaust ports are both open for a while at the same time. 

If I remember correctly, it was discovered that a three cylinder looper was magic exhaust tuning wise as the timing of the exhaust "note" from one cylinder could block the exhaust port opening of one of the other cylinders (not sure which) at the right time, making for more fresh fuel captured in that cylinder, boosting output and probably boosting fuel economy, potentially lowering piston dome temperature, and reducing pollution. 

I am wondering though if there are water passages in there somewhere which are metered in a way that helps to correct the tuning timing of one or more of those exhaust circuits to compensate for the difference in length of the exhaust "headers" leading into the common tuned pipe.

I was just looking at that picture again and I'm wondering if that water being dumped into the exhaust system is to lower the tuning of the relatively short exhaust system.

I did some pipe design work for a friend some years back who was racing A and B modified hydros running Champion Hot Rod motors and the pipe program I was using called for an overall "tuned length" of the expansion chamber (from the side of the piston down through the center of the header, diffuser, dwell and halfway down the reflection cone at the back of the pipe) to be around 42" long tuned for 7,000 rpm.  Those ran like scalded dogs.

I'll bet Joe McCauley knows a lot about this.

Cheers,

M
1957 FC Rocket -'58 Evinrude Lark 35
1958 FC Hawk 1-'59 Evinrude Lark 35 (and J-55)
1960 Starcraft 12' open boat-'76 Evinrude 25
1965 era McCorvey 3-point hydroplane-'52 Mercury KG-7H
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Last edit: by Merky Johnrude.

Triple Threat 19 Feb 2024 21:44 #128114

Here is a light shining through the water port into the exhaust on the 45 cubic inch OMC looper. This is at the lower end of the upper cylinder exhaust port, once the exhaust ports exit the block they combine in the tuner into one port.
I have not found it on the 70 HP triple yet but I’m betting it’s there somewhere. There is a water port into the tuner on the 70, that might be the only one.

A question for John: how does the length of the exhaust port impact jetting? The ports are certainly not equal length.


“Keep thy shop and thy shop will keep thee”
- Poor Richard’s Almanack, 1737

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Last edit: by Locomotion.

Triple Threat 25 Jan 2024 01:54 #127919

Looks like you’re having fun Ray. It is fun to watch.








It makes me want to say, hold my beer ;-)
“Keep thy shop and thy shop will keep thee”
- Poor Richard’s Almanack, 1737

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Triple Threat 25 Jan 2024 00:12 #127916

Oh Ray , the need for speed!!! Your work is amazing!

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Triple Threat 24 Jan 2024 17:10 #127913

Looks like you’re having fun Ray. It is fun to watch.








Hey scoot, the fun starts when this baby is hanging on the back of some Feather Craft ;-)
“Keep thy shop and thy shop will keep thee”
- Poor Richard’s Almanack, 1737

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