Where do I find the right jug for my engine?

[Street Ryderz]

I don't need a perfectly ported cylinder. I just need something that isn't designed for the 40mm stroke vs the 38mm stroke because then I need to stack gaskets and sand off about 3 mm off the top of the cylinder which isn't ideal because one side may sand a bit too much and cause the piston to hit the head. Raising the head only kills the squish band in the process.

The difference between a 40mm stroke jug and a 38mm stroke jug is 1mm in height it's also 1mm in the height and depth of the stroke.No gasket stacking or shaving 3mm off the deck is needed.It's the crank/rod and piston type that determines the piston height in the cylinder.

 

[Hell on Wheels]

The difference between a 40mm stroke jug and a 38mm stroke jug is 1mm in height it's also 1mm in the height and depth of the stroke.No gasket stacking or shaving 3mm off the deck is needed.It's the crank/rod and piston type that determines the piston height in the cylinder.

I've found that not to be the case. For some reason, the 38mm stroke type b piston will top out where the 40mm would (at least on the cylinder I have; could it be a pk80 with 40mm stroke and a type A piston?) but then only uncovers half of the transfers and exhaust ports. So either the cylinder seat on the engine is lower by 1mm or the cylinder bottom is 1mm too short or the crank is 1mm higher than it should be is how I see it. The gasket stacking and deck shaving is what I needed to do get the ports fully uncovered at BDC. Don't know whats going on exactly here...

 

[Street Ryderz]

I've found that not to be the case. For some reason, the 38mm stroke type b piston will top out where the 40mm would (at least on the cylinder I have; could it be a pk80 with 40mm stroke and a type A piston?) but then only uncovers half of the transfers and exhaust ports. So either the cylinder seat on the engine is lower by 1mm or the cylinder bottom is 1mm too short or the crank is 1mm higher than it should be is how I see it. The gasket stacking and deck shaving is what I needed to do get the ports fully uncovered at BDC. Don't know whats going on exactly here...

Transfer and exhaust ports don't need to be fully uncovered.The important part is crown to deck height.None of these engines expose the full window,at the time the window is fully exposed it's not doing anything that the extra area can help.

 

[Hell on Wheels]

Transfer and exhaust ports don't need to be fully uncovered.The important part is crown to deck height.None of these engines expose the full window,at the time the window is fully exposed it's not doing anything that the extra area can help.

Alright, I'll install the cylinder I have the way it is unmodified and I'll measure off my durations and post them once I get home. I will be surprised if they are more than 100 degrees exhaust or transfer. You probably remember how I raised the cylinder to increase duration on the CDHpower DIO reed cylinder. The problem is it broke before it got a chance to run so I don't know what power I could have made.

 

[Hell on Wheels]

Interestingly, it seems Fred sent me a GT-5 Super bottom end which uses the 40mm jug but the deck needs shaving. Because the piston bottoms out at the bottom of the port without raising the cylinder and is a few mm too short in the bore. Or I just have a weird cylinder. Or my previous engine is some weird outlier because of the cylinder/head design so it's possible they screwed about with the crank

 

[Street Ryderz]

Interestingly, it seems Fred sent me a GT-5 Super bottom end which uses the 40mm jug but the deck needs shaving. Because the piston bottoms out at the bottom of the port without raising the cylinder and is a few mm too short in the bore. Or I just have a weird cylinder. Or my previous engine is some weird outlier because of the cylinder/head design so it's possible they screwed about with the crank

How far is the crown from the deck? And is that with a high or low pinned piston?

 

[Hell on Wheels]

How far is the crown from the deck? And is that with a high or low pinned piston?

2.5mm. It's a high pinned "type b"

 

[Street Ryderz]

2.5mm. It's a high pinned "type b"

That's alot to deck off the top,I'd be raising and see how a low pinned fit's just to be sure.

 

[Hell on Wheels]

That's alot to deck off the top,I'd be raising and see how a low pinned fit's just to be sure.

Yah, I don't have a low pinned piston on hand and I already decked it. I've set my squish to about 0.8mm (maybe slightly less) and cleaned up the ports, installed the engine, etc. I tried starting it without the expansion pipe (pita to install over my huge bottom tube) and I think either the cdi is acting up, my tune needs a complete redo, or it's not liking that the exhaust is missing.