I'm a porting idiot.....

[Trent Curtis]

found a not running 288 for dirt cheap-

Tore it all the way down Got it out back together.

For some idiotic reason I decided to try to do some shaving on the cylinder to giver her some extra air.... but I didn't want to change the timing.

Here's what I did..... slightly widened the exhaust port, but not much.

Took material off the roof of the intake port, hoping this would give better air flow. In hindsite im thinking that roof was slanted down , or choked off to help direct towards the crank.

I opened up the transfer ports on the INSIDE only. I didn't mess with the transfers as they open up to the bore.

Here's my question...... after running it I'm getting no more RPMs and I lost my bottom end. It seems to stall out easier than my 281 (which is opened up on the exhaust/intake but nothing on the transfers).

Opening up those transfers...... was that a mistake? See pics.......

If I ruined a 288 cylinder I'm gna sentence myself to a life Of husqvarna purgatory

 

[Trent Curtis]

I'm worried I gave it volume- but I messed up the fuel/air velocity into the crank and from the crank to the Combustion chamber.

 

[Trent Curtis]

Better pic of the intake- other one had a weird look with the lighting

 

[pioneerguy600]

What`s your compression?

 

[cus_deluxe]

And have u looked at piston since youve done the work? Ports look a little sharp, maybe could use some more beveling.

 

[cus_deluxe]

Intake and exhaust ports i mean

 

[blsnelling]

I don't see enough porting changes to affect much of anything. Something else must be going on.

 

[Trent Curtis]

So compression is pretty weak- 140psi

Piston and cylinder are clean as a whistle - piston ring looked pretty good.

I guess I should do a gasket delete (squish proving acceptable .20) and maybe a new ring.

 

[Trent Curtis]

I don't see enough porting changes to affect much of anything. Something else must be going on.

So am I right in thinking that my "changes" aren't changes at all since I didn't change the transfer port openings to the bore?

The intake was def opened up a fair bit. Exhaust I just cleaned up and widened the edges a bit.

 

[blsnelling]

Make sure didn't raise the intake until the rings are dropping into them. That's a deal breaker. Nothing else you did would have much affect at all. You didn't change anything at the cylinder wall where it really counts.

 

[Trent Curtis]

Make sure didn't raise the intake until the rings are dropping into them. That's a deal breaker. Nothing else you did would have much affect at all. You didn't change anything at the cylinder wall where it really counts.

Mmmmmm..... good call I didn't even think of the rings on the intake port.

I'll check first thing in the AM.

But opening up the intake/exhaust at the cylinder wall as I did..... how does this have no effect? I believe you as i didn't get any positive performance change. But it seems like it should charge the crankcase better with a larger breather?

I do see that my t-ports were in vein.

 

[blsnelling]

Did you widen the exhaust at the cylinder wall or the flange? If at the wall, how much? You should have seen some gains.

 

[Trent Curtis]

I widened at the wall and the flange. Not much- more or less took a good portion of the taper out of it.

It does run really smooth now. Just slows down easier than a 288 should.

Bsnelling- I've never fully understood how directly compression relates to torque/power.

140 is def lower than ideal!

 

[Gugi47]

So compression is pretty weak- 140psi

Piston and cylinder are clean as a whistle - piston ring looked pretty good.

I guess I should do a gasket delete (squish proving acceptable .20) and maybe a new ring.

1-That's because you carved in the piston.
2-You carve to much of from the top of the intake. You should go wide on the side and take last from the top.

 

[Trent Curtis]

1-That's because you carved in the piston.
2-You carve to much of from the top of the intake. You should go wide on the side and take last from the top.

What is because I carved on the piston? And what do you mean "carved on piston"?

It has same compression after I worked over as it did before-

I don't see how the intake could have hurt anything- if you go too wide you can catch a ring. Biggest area of harm I could see would be lowering the velocity of the fuel/air coming in.

But please explain- happy to learn.

 

[Trent Curtis]

And to clarify what i did to the intake- I simply made the bore side the same size as the flange side. It choked down quite a bit going into the bore..... the roof was slanted down. In hindsite I'm thinking this is to direct flow better downward to the crankcase.

 

[Cease232]

1-That's because you carved in the piston.
2-You carve to much of from the top of the intake. You should go wide on the side and take last from the top.

That one went over my head as well?!?


Sent from my iPhone using Tapatalk

 

[Trent Curtis]

Blsnelling, and Westcoaster90- enlighten a troubled soul!

 

[Rio95]

I doubt that your porting is what made you lose you bottom end torque. Your mods don't seem significant at all.

Raising the intake is considered by some professionals to be a valid way to increase flow through the intake port, however, rings dropping into the port is not ideal. However, providing you don't have the top ring dropping into the port, this is not a deal breaker. I have seen several stock saws that the bottom ring drops into the intake, you just have to make sure the top of the port is shaped properly so it doesn't catch a ring.

Bevels on the port edges are important, and I looks like you don't have them. I use a ball stone to put a small bevel on the edge.

I recommend reading some of the porting how to threads, and you will understand what I am saying better. One that helped me is http://www.arboristsite.com/community/threads/porting-the-361-big-bore.85488. Read and re read it, and search this site for more info on anything you don't quite understand, I use a site specific Google search e.g. porting site:arboristsite.com.

Also, reading the 12 saws of Christmas threads on O P Eforum.com taught me a lot more. There are some good discussions there.

Hope this helps

 

[Gugi47]

What is because I carved on the piston? And what do you mean "carved on piston"?

It has same compression after I worked over as it did before-

I don't see how the intake could have hurt anything- if you go too wide you can catch a ring. Biggest area of harm I could see would be lowering the velocity of the fuel/air coming in.

But please explain- happy to learn.

You losing compression true the intake......