Yamato 302 Ports

[Systemoverload]

I noticed that the exhaust port edges on my engine are quite sharp. I am just using my fingers through the exhaust tuner to feel the edge. Is this normal? I am concerned about premature engine wear with the sharp edge scraping oil off the rings and piston. Do you folks radius the port edges so it's not as sharp? How do you do it?

Thanks!

[B Walker]

In APBA you can't touch a 302 port in any way and it is one of the very first things the APBA inspectors look for.

There is no issue of premature wear due to the sharp leading edge of the port.

BW

[Tim Weber]

Not quite so Brad, you are allowed to break the edge but not chamfer it.

Don't take a dremel tool. I use my finger and a little 320 paper to dull the edge. A ball hone will do the same thing.

Yes, those sharp edge will hang a ring once in a while or scuff a piston.

Tim

[B Walker]

hmmmmmmmm

Not so sure on this one Tim. Your gonna have to point out the rule to me that allows breaking that edge....heres what I have:

From Page 68 of the Stock Outboard Inspection Manual:

2. Addition or removal of metal on any cast or forged internal engine components, surfaces or passages including the intake system, carburetor, or exhaust system is prohibited. Honing of cylinder bores and connecting rods is permitted.

It may make sense it would hang a ring or scuff a piston because that happened often enough with the Mercurys which have ports half the size.

But in so many ways the Yamatos dont do things we found common on the Mercs

I have not met the person that has has hung a ring or scuffed a piston yet with a 302 due to a sharp leading port edge.

Maybe Tom Johnston or one of the other Yamato gurus will post here.

All I know is that multiple inspectors at teardowns for me have gone straight to the head, then the ports and felt that leading edge. It is a point of emphasis by the inspectors.

BW

[EKorpe]

302 port

pop the sleeves out and have fun ? done many ! keep them inspectors on their toes ?

[Matt Dagostino]

Rings...........

I am no motorhead but i believe engine builders are very careful to 'massage' the ring edges before installing to avoid catching a exhaust port edge........it is permissable to do that with the rings. The 302 is more prone to that sharp edge catching than the older model 80 and 102 Yamato's.

Have fun

[B Walker]

Uh-oh

I see an agenda item for next years SORC!

BW

[Tim Weber]

Never doubt the Captain!

Tim

[propnuts]

For us no problems

Been running the 302 for a few years now, never touched the ports, never had a problem. I am also far from a motorhead, but my general observation is that these motors are so well machined that a lot of things that used to be problems on other motors may not be problems on this one.

[kampkurz]

T J Says:

Just talked to TJ Friday about ringing a 302. He mentioned that the ports on a 302 can be very sharp and can possibly breaknew rings. I asked what is done to keep new rings from breaking after re-ringing, and Tommy replied a ball hone does a nice job of taking care of the problem. I'm no motor head either, but I can imagine what Tommy is talking about. I'll just assume he know's.

[me-otch]

Port Edges

Someone more knowlegeable can correct me but..
You want to be careful if your just using your finger and some sandpaper because you could potentially raise the port timing. Flex hone is your best bet,
sounds stupid and to small to worry about but i read somewhere that when the guys punch out the OMC A motor they do not champher the port window because it can very slighty raise the port timing and when they get inspected the get tossed.

I would just keep this in mind if you choose to do so....

[Systemoverload]

I did notice that the area above the top ring (on the piston) doesn't have any carbon build-up compared to the area below the ring, possibly indicating that some scuffing is indeed happening? I think I'll use sandpaper very lightly, just enough to put a slight radius.

Thanks for all your replies!!!

[B Walker]

So the "by the book" answer is that you can't touch the port in any way.....but everyone does it so it is OK?

This is the same thought process that brought us a blocked water passage in OMC 15.

Everyone is worried about hanging a ring on the sharp edge but has anyone done it? I dont mean a "but I heard about Fred once back in '89 in his C2R" story.

I mean the actual person that has hung a ring. Or the motor builder that had to resleeve a block due to scoring from a hung ring.

Until then, I will maintain that breaking the leading edge of the port in any way other than using a ball hone is a solution without a problem.

BW

[Dave M]

?

Are you guys talking about 302 Mod hydro or CMH ?

[B Walker]

Dave, I quoted the APBA Stock Rule from the SO Inspection Manual earlier but you made me go look up the 500CC Mod rule and it is even more specific:

From pg 39 of the 2011 Mod Inspection Manual:

6. Internal machined surfaces may be re-machined as long as minimum and maximum dimensions are maintained. Cast surfaces must remain as cast with no alterations, abrasive blasting or polishing.

Note: It is not permissible to re-machine surfaces that do not have specific dimensions.

interesting......discuss

BW