Piston problems

[gary55]

Your right! alot easier to deck it but adding rod length and a little lifting of the jug gives more displacement and slight advance of timing and I'm all ways looking for more lol!

Come on now Ryderz you know you can't gain displacement by adding rod length or jug height. That's all dictated by stroke no mater where it is occurring in the cyl.

 

[Street Ryderz]

Come on now Ryderz you know you can't gain displacement by adding rod length or jug height. That's all dictated by stroke no mater where it is occurring in the cyl.

yeah your right! I forgot about the crank circle when I swap things around witch alters the stroke my bad!

 

[Purple Haze]

Where are you getting these longer rods? I have been looking into modifying rods anyway. I learned long ago that rod length has a dramatic effect on torque and bore wear. If the deck height difference is only 3mm that would be fixed with extra or thicker base gaskets.

 

[crassius]

don't forget rod weight making a difference also

I'm finding a minor annoyance with using two thick base gaskets too - seems they compress over time, requiring at lot of attention to head retorquing.

 

[Street Ryderz]

Where are you getting these longer rods? I have been looking into modifying rods anyway. I learned long ago that rod length has a dramatic effect on torque and bore wear. If the deck height difference is only 3mm that would be fixed with extra or thicker base gaskets.

there are two rod lengths 85mm and 90mm the zaf80 shown on the right for b type engines and the zae50 or 60 or the short zl rods for a type engines,there is also a long zl rod for the b type engine! There is almost 1mm difference in jug height between the two and some cranks have it's big end 1 -2 mm closer to the center line,So if you take the long rod with a lower big end and the taller jug there is only 2-3mm to make up for at the deck!Alot of these engines come stock with the crown coming atleast 1mm below the deck and the difference between the a and b pistons pin height is 5mm if the op had put the wrong piston in it would sit 4-5mm from deck to crown as in the pic below and be very noticeably wrong!

 

[Purple Haze]

Thanks for the info, Street Riderz>. My experiences have been that the piston sits below the deck, so changing the rod centerline could fix this. What are your thoughts on off-set boring the small end and rebushing? My opinion is that the needle bearing is not the way to go, a proper bushing would be much quieter. Press fitting into the rod would solve the reliability issues.

 

[Street Ryderz]

Thanks for the info, Street Riderz>. My experiences have been that the piston sits below the deck, so changing the rod centerline could fix this. What are your thoughts on off-set boring the small end and rebushing? My opinion is that the needle bearing is not the way to go, a proper bushing would be much quieter. Press fitting into the rod would solve the reliability issues.

there are bronze oil lite bushings that can be used but are getting hard to source,they are not press fit into the rod but still work well!the last batch I received are a little short as they are only 13.5mm in length and would prefer 15-16mm but I keep looking for more sources.As for off set boring the rod these engines really benefit from getting as much piston drop as possible to expose more of the transfer and exhaust so as Gary said decking the cylinder top is the easy way!unless you have a lathe and a mill and the skill set to change the crank circle than you have to go thru all the varrients to find one that is closer to center than the norm and then we are only talking about 1-2mm difference.also imo most of the rattle like noise comes from the bevel gear and clutch gear resonating thru their cover!

 

[2StrokeMama]

Just thought I'd quickly add, BASE gaskets can be made out of any ol cereal box. They've worked great for me and many other people who use them. Just coat both sides with spray gasket and dry.
And I think replacing that cyl would cost you better in the end. I feel like timings would be thrown off and maybe even not enough compression...
- just my thoughts

 

[gary55]

there are bronze oil lite bushings that can be used but are getting hard to source,they are not press fit into the rod but still work well!the last batch I received are a little short as they are only 13.5mm in length and would prefer 15-16mm but I keep looking for more sources.As for off set boring the rod these engines really benefit from getting as much piston drop as possible to expose more of the transfer and exhaust so as Gary said decking the cylinder top is the easy way!unless you have a lathe and a mill and the skill set to change the crank circle than you have to go thru all the varrients to find one that is closer to center than the norm and then we are only talking about 1-2mm difference.also imo most of the rattle like noise comes from the bevel gear and clutch gear resonating thru their cover!

You have probably already checked these guys out but if not, NSK, AST, Beemer Precission, and Bowman have a selection in comparable sizes and will custom size as well.

 

[2StrokeMama]

This seems strange to me to get a longer rod if this bore is not bigger than your last? Why don't you get a bigger piston and a cylinder bore attachment and bore up your kit?
Edit: and if you are careful you can slightly bring down the top of the piston so that when at BDC it sits more flush with the bottom of the ports for best cooling.
We are talking about a portion of the piston not the whole crown of course.