372xp big bore kit..do i or dont i.

[wisecobandit]

Hopefully this works

Big bore standard inlet port

 

After

 

Standard big bore exhaust port

Just a small tickle as it didn't need much

 

Standard lower transfers on bb kit

Lets say they are opened up well...

 

Didn't take a before piston shot doh... but it looks like this now.

 

Just need to do a slight bit of cleaning and polishing up and its done.

Plus it should be a little lighter now...

[wyk]

Nice. Yeah - it's the same jug I've got.

[spudulike]

Hopefully this works

Big bore standard inlet port

 

After

 

Standard big bore exhaust port

Just a small tickle as it didn't need much

 

Standard lower transfers on bb kit

Lets say they are opened up well...

 

Didn't take a before piston shot doh... but it looks like this now.

 

Just need to do a slight bit of cleaning and polishing up and its done.

Plus it should be a little lighter now...

 

Humour me here - that piston...is supplied with the kit?? It has two rings?? and I guess you have windowed the sides?

 

The standard SINGLE piston ring ends come nowhere near the inlet port or upper transfers....have you checked to make sure that the ring ends don't come anywhere near the openings (Inlet or uppers) - at least within 2mm!!

 

If they do then the rings will snag - just one of the things you need to watch out for.

 

The other...sorry to be a pisser on the fireworks....... does the inlet port get covered by the width of the piston skirt, if it doesn't, you will get lots of blowback through the carb when the piston lowers:thumbdown:

 

The last thing - how much did you raise the exhaust port by - I hope it wasn't a .....grind until I am bored affair:blushing:

 

Oh - BEVEL the port edges - sharp port edges are your enemy - use a curved diamond rifler file - ignore the warning at your peril!

[wyk]

Nice. Yeah - it's the same jug I've got.

 

Wait - that intake is REALLY wide. It doesn't free port at that width?

[spudulike]

Your gonna hate me for asking:blushing: the bottom of the exhaust port should be level with the piston crown so neither the piston or port impede the flow.....yours looks a little lowered:confused1:

[wyk]

Humour me here - that piston...is supplied with the kit?? It has two rings?? and I guess you have windowed the sides?

 

The standard SINGLE piston ring ends come nowhere near the inlet port or upper transfers....have you checked to make sure that the ring ends don't come anywhere near the openings (Inlet or uppers) - at least within 2mm!!

 

If they do then the rings will snag - just one of the things you need to watch out for.

 

The other...sorry to be a pisser on the fireworks....... does the inlet port get covered by the width of the piston skirt, if it doesn't, you will get lots of blowback through the carb when the piston lowers:thumbdown:

 

The last thing - how much did you raise the exhaust port by - I hope it wasn't a .....grind until I am bored affair:blushing:

 

Oh - BEVEL the port edges - sharp port edges are your enemy - use a curved diamond rifler file - ignore the warning at your peril!

 

On this set up, he can run a single ring on the top. It also has the benefit of the pin being centered directly above the intake port. I will likely run mine with a single ring and no bottom gasket.

[spudulike]

Wait - that intake is REALLY wide. It doesn't free port at that width?

 

Bingo - think we have hit the same issue - the inlet port on a 372XP is pretty wide as it is - around 1.5mm off each side is all I can manage to get a good seal!

[spudulike]

On this set up, he can run a single ring on the top. It also has the benefit of the pin being centered directly above the intake port. I will likely run mine with a single ring and no bottom gasket.

 

Yes, but the point is where is the ring end on this two ring piston - guess you could re-site the location pin and using one ring was an option I had thought of.....gotta go, steak is on the BBQ:thumbup:

[wyk]

Yes, but the point is where is the ring end on this two ring piston - guess you could re-site the location pin and using one ring was an option I had thought of.....gotta go, steak is on the BBQ:thumbup:

 

He did mention he was considering using a Stihl 52mm piston. I dunno what one looks like exactly off-hand.

 

The piston I have here, the same one that comes with the kit he is porting, has the ring-end right above the intake if you only use the top ring. The other end is , of course, askew of that. Al runs only the top ring in the same kit and has hundreds of hours on one without any problems.

 

Also, I doubt this piston will cover the intake he has there. I didn't open my nearly so much, and I have mebbe 1mm on each side(same with my exhaust).

[wisecobandit]

Both ring ends run thru the inlet only and don't come anywhere near any other port.

 

The piston skirt covers the inlet tract by 1.2mm or so so close but we shall see...

No the exhaust hasn't been lowered. just the rough casting removed and polished up. Raised by 1mm.

 

Like I say its my own saw so you have to push things a little to find out what does and doesn't work,

Edited August 7, 2013 by wisecobandit