Yamato 80 break in procedure

[Bob Rusnak]

Sounds like the original engine was modified for the RB class in PRO outboard division. When the new Quincy engine came out it ruined the class and it was dropped. The engine now could have been used for a C mod engine. Too bad you can't find out who owned it. The McKean's are from Texas.

[Steven27jack]

Still haven't removed prop, alot of this stuff I have to get help with, or find a way on my own, hence the clamp to try to remove the pin, because I use a wheelchair to get around, and my hands don't work so well, I.e. I can't easily hold onto a hammer and punch at the same time. This entire go-through has been a process for me, but I refuse to give up. When I got engine, rings were stuck, and it only had 60psi and 40psi on cylinders, 40 being top. Ring gaps were .6mm on used rings, still a bit of life was left aye?

As far as exhaust, I don't believe I can run it without a tuned pipe or internal megaphone correct? Wouldn't doing so result in burning/seizing pistons due to too short of exhaust?

[ZUL8TR]

If you want to pulse pump it with remote tank there is a hook up available at BTM, This will give you more water time with more fuel on board. The gravity tank is about 15 min at full bore, but plan on 10 to get back to the launch.

https://btmco.com/product/3250-yamat...its-80102-302/

Have you removed the prop?

A cold compression test will probably tell what the .120 mod might mean. My cold Y80 with throttle open full pulls 150 psi in 4 rope overs with my gage. I do them cold so temp is a fairly constant value compared to doing it hot. It is only a reference for engine condition so keeping things fairly constant for relative results is important

[Steven27jack]

These are two pictures of "complete" I have right now. The cylinder head has "modified .120" stamped on it, I'll be getting a picture of that later, as well as the tag on the lower unit. The intake is drilled for a pulse pump application, the gentleman that I got this engine from said it had no fuel tank, so I'm guessing it was setup with a remote fuel tank and pulse pump. I bought this engine from Facebook marketplace for $800, from an older gentleman that restores antique outboards, but he gave in I believe when he couldn't get the prop off, and sold it, I bought it. Wish I knew who he bought it from...

[Bob Rusnak]

Hopkins made the prop for Jim McKean. He always put the name on the prop who ordered.

[Steven27jack]

I used the clamp method, and with all my might got the pin to move 3/16" one way, saw a gap on the side I pushed out between the pin and prop, so I'm guessing that side is the smaller tapered end, it was flared so I filed the sides of the pin to make it round again. Sprayed pb blaster, again, have been, put the clamp back on it and forced it the other direction, but still just as hard to move...it's not coming easy, next going to lay the lower unit on its side and figure out how to support prop and shaft, and try driving it out with a punch a little smaller than the pin.

[Steven27jack]

I just pulled the powerhead back off, and the internal megaphone is missing. I'm guessing because it was running the header exhaust, the previous owner before me was trying to build it back to stock, but gave up early. He did get the exhaust manifold, which wasn't on the engine when he got it from I don't remember who, it had the header setup, but no pipe. Should I set it up with a tuned pipe? If so, where should I find one? Also had a thought of buying a newer modern 31mm or 32mm mikuni carb that I am more familiar with, and be able to tune easier. I could also run regular pump gas without damage to engine correct?

[Steven27jack]

I also have this exhaust header, and the tuned pipe support bracket, but no tuned pipe. The carburetor in the manual says its a mikuni, but the carb on the engine is a bing. Any thoughts if this was setup with a tuned pipe it's last time running?

[Steven27jack]

I have the manual download, it says it's supposed to have a mikuni carb on it, it has a bing carb. Engine is a '76 I believe, don't know if it came with a bing carb that year or if it's a different carb. I was wrong about one of the jet numbers, one is 55, the other 60. Doesn't match description of jets in manual, same with float, it says set to 1", it's shorter than that I believe.

I understand what your saying about the exhaust now, pulling the powerhead back off to check it

[Steven27jack]

No I used a 3 stone glaze buster from orileys

[ZUL8TR]

The other side of the prop has Hopkins is that different than McKean or was it reworked and stamped?

[ZUL8TR]

So all you did was glaze bust the cylinders with X hatch and the same pistons went into the same cylinder and the clearance is what it was + a smidgeon more due to glaze bust. Did you use a ball hone for the glaze bust?

[ZUL8TR]

The spark plug 18 x 14 mm adapters - call Tom Cronk he may still have some left. They are also available at local auto stores. If you need details on trimming the adapter to correct length and other details to fit the 14mm x 3/4 reach NGK plugs let me know.

You said - "I don't believe the exhaust was lower than the cylinder block, but I can loosen the powerhead and loosen the exhaust and shim the block with feeler guages then retorque the exhaust then powerhead to get that better seal.


I am not referring to the exhaust part on the block as you state, that should be level to the block per manual. I am referring to the megaphone in the exhaust tower. I set the megaphone top of flange about 0.003" above the exhaust tower perimeter flange so the seal of the block exhaust port is better from some additional gasket squish due to the 0.003"rise. The mag is shimmed with thin alum (beer can) or other. I use a hole punch to make a hole for the megaphone bolts and trim round with a scissor and shim as need under the mag flange for the 3 bolts. When the megaphone is unbolted and removed you will see the factory shims there. Check shimming of megaphone flange in all directions. Details available.

Set float in carb per manual. The manual states 1.5 turns for the high speed jet I find about 7/8 open works for me - testing and plug reading per fuel octane, oil ratio, timing, plug used, etc.

Do you have a Y80 manual? Here is Ric Montoya site for them"

http://yamatoracing.com

[Steven27jack]

I used a depth dial guage to check the advance on both points, but do not have a buzz box. I used cellophane between the points to check when they break by feeling the tension and slowly rotate flywheel till I feel slippage, both points seemed to break around .18 to .20. As for the mag, it doesn't have locks, just push it right all the way. Just going to be lake playing for now, don't know of any racing in Texas.
I believe I have 18mm spark plugs holes, where would I be able to get adapters?
I don't believe the exhaust was lower than the cylinder block, but I can loosen the powerhead and loosen the exhaust and shim the block with feeler guages then retorque the exhaust then powerhead to get that better seal.
I got the carb apart today and started cleaning it, was very green and nasty. The two jets I noticed have 55, and 80 on them, other than main jet.

I do not know the diameter and pitch, but I can measure diameter tomorrow.
I know it's sharp as a razor, cut the absolute crap out of my hand a few months back being stupid lol

[Steven27jack]

I had a machinist buddy of mine measure the cylinders with a telescoping guage and micrometer, and measured pistons with micrometer at x1,x2,x3, y1,y2,y3, got difference between the two then divided by two, which should be piston wall to cylinder wall clearance