Porting my 361

[blsnelling]

You guys have gone and made me do it. I knew I eventually would someday. I checked the compression and measured the squish before I tore it down.
Compression(cold) = 168 psi
Squish = .024-.025"

My goal is .017"-.018" for the squish. When I had a ported jug on this saw by another builder, the squish was a .016" and it was fine. The problem is that I do not have a mill or lathe to deck this jug with. This cylinder protrudes below the mounting flange so it cannot be sanded on a flat surface to deck it. I measured the base gasket and it's .015" so I can't go just go without one. That would put me at .010" squish, way to tight. Sanding and polishing my 460 piston removed about .006". I think I'll just remove .007"-.008" from this piston and go without a gasket afterall. The only other option I can think of would be to go with a very thin gasket of some kind. I've heard some mention a grocery bag. That kind of scares me. I want this to be durable. I'd appreciate your input on this matter.

Porting will be done similiar to my 260 and 460. I will widen the ports as much as the skirt will allow. I will only touch the top of the exhaust enought to clean up the casting and give it the shape I want. I will not be raising it. This is a work saw and I want torque, ie compression. I will not be lowering the intake port either, only widening it. I will raise the tranfers only enough to make up for the few thousandths I drop the jug. Again I don't have the proper tools to get in there and do much anyway. I do all this work with a Dremel, files, and sandpaper.

Here's some pics I took before getting started.

This P&C only has a handful of tanks through it.
Intake side.

Exhaust side.

Transfers. Notice the huge sloppy bevels on all the ports.

Intake port. It has the same strange little hole my first jug did.

Exhaust port

Notice the scribed lines where I'll be opening it up to.

Here's a very interesting side not. This saw has been used with Maxima Castor 927 oil @ 32:1. I won't be doing that again. I've already switched over to Klotz R50 synthetic. BTW, I found the same carbon build up on the 460 piston. I did not take a piture of it though.

 

[Jacob J.]

If you lower the jug by running without a base gasket, you should still at least return all the ports to the stock timing. Realizing that you'll be widening the ports and that you want a torquey saw, if you don't go back to the stock timing I think you'll be robbing yourself of RPMs unnecessarily.

 

[Lakeside53]

Your piston tops looks similar to most 361's I take down... maybe not as crystaline, and no matter what they run. I love the plugs -one side of the insulator is often white and the other black.

 

[blsnelling]

Your piston tops looks similar to most 361's I take down... maybe not as crystaline, and no matter what they run.

My 460 looked very similiar with lots of carbon.

 

[Lakeside53]

50:1

Ultra

 

[blsnelling]

I forgot to mention, I'm running the Klotz at 40:1.

 

[blsnelling]

The ring end gaps are in unusual locations on this 361. The top ring gap is right in the middle of the intake port. That's probably why you see the marks there below the intake port. My question is with the lower ring gap. It is almost exactly even with the edge of the piston skirt. How much surface area does it need beside the exhaust port?

 

[Four Paws]

I will only touch the top of the exhaust enought to clean up the casting and give it the shape I want. I will not be raising it. This is a work saw and I want torque, ie compression. I will not be lowering the intake port either, only widening it. I will raise the tranfers only enough to make up for the few thousandths I drop the jug.

Why are you going raise the transfers if you aren't going to raise your exhaust?

 

[blsnelling]

I'll basically grind until the factory bevel is gone and then rebevel. That's how I did my other two saws. I've got the intake and exhaust ports roughed in. I've got a lot of sanding to do to get the exhaust polished up. I haven't touched the transfers or the piston yet either.

I'd open this up a lot more, but the intake boot is this small. To go bigger would actually be worse.

 

[Jacob J.]

At least you'll be back at the stock timing and that's good.

 

[Andyshine77]

Nice clean looking work Brad.

 

[blsnelling]

Nice clean looking work Brad.

What are you doing up this crazy time of night? I can't seem to quit working on this thing.

 

[blsnelling]

I'm supposed to be in bed but can't seem to quit working on this thing! the piston's done. I took .007"-.008" off the top and polished it. Tomorrow I'll have to get some more sandpaper to finish off the exhaust port and a stone for the transfers. Bevel the ports and I'll be done. The muffler was already modded.

Here's how it started.

Here it is now.

 

[5shot]

Looking forward to the video

 

[NPKenny]

... I took .007"-.008" off the top and polished it....

I am following this thread intensely as the pictures and description, along with those included in the 460 thread, are exactly the information I have been searching for.

What is the benefit of taking the .007"-.008" off of the top of the piston? Is this to allow you to take the base gasket off the jug and get your compression dialed in? I saw where you had put a mirror polish on the 460 piston, but I didn't notice a reference to that much milling.

Again, thanks much for sharing the experience with us. Please be as diligent with the transfers.

 

[blsnelling]

My 260 and 460 both are flat on the bottom of the jug. I was able to "deck" the jug by sanding it on a flat surface. This lowers the jug in order to get my squish where I want it and still use a base gasket. With the 361 you can't do that since the cylinder walls protrude from the bottom of the jug. On the 361 I'm removing the base gasket. Alone, this would have my squish too tight. I was going to sand down and polish the top of the piston anyway. So I measured it before sanding and just removed the .007" I needed to get my squish where I wanted it. EZ PZ.

 

[NPKenny]

As I suspected... Thanks for the clarification blsnelling.

 

[blsnelling]

When there's a will, there's a way! I didn't get in bed until 4 AM this morning. Everything's done except polishing up the exhaust. The transfers have been tweaked, dividers sharpened, bevels ground, piston polished. After work I'll go get some more wet/dry sand paper and finish up the exhaust and hopefully get it put back together.

 

[TwinTurboRam]

Brad,

Didnt take you long to get on the 361 project Did you already finish off your 260?

 

[blsnelling]

I decided to do the 361 first. the 260 is already ported, but I need to go in and do the piston like the others. I'll recheck the shape of the exhaust port while I'm at it.

You know this is all your fault. "Hey Brad, when are you going to do your 361?":hmm3grin2orange:opcorn: