PlanetMinis Forums banner
1 - 17 of 17 Posts

·
Registered
Joined
·
2,317 Posts
Discussion Starter · #1 ·
SPECS.



what is the optimum ring end gap for:

top ring =

2nd ring =

oil rings =



I have heard soo many different specs I figured I would throw this up and see.....



What is the optimum piston to wall clearance?
 

·
Registered
Joined
·
4,688 Posts
looking at about 3 thou. piston to cylinder clearance. There is a rough mental math equation to get an approximate ring end gap.



I was running about 16-20 thousandths on the Indian Four rebuild we were doing at school. We didn't measure the oil ring.. as there isn't really a good way to check it. cyclerider would be the one to ask... but there is something to start from.



*Found something... looking at about 4 thousandths per one inch of bore diameter for a rough idea. Say you are running a 52mm bore...common 88 kit. 52mm /25.4mm per inch = 2.047 inches. 2.047 inches times 4 thousands per inch = 8.2 thousandths roughly. Thats what the math says... not sure if that applies to small bore engines like it does to a chevy 350... kurlon... cyclerider?
 
G

·
Everything depends on the engine, piston, cylinder, coatings, etc...



.003" piston to cylinder clearance is a lot with the size of pistons we are working with. Try more like .002" as the maximum before piston replacement. I like about .001"-.0015". A lot of bolt on kits are around .003" though stock. A bigger gap can give you more power because it runs more freely but it won't last near as long.



As far as ring gap... I like...

.010"-.015" for compression rings. Not more than .020"

.018"-.022" for oil rings. Not more than .040"



Warning. Tight can cause issues if the piston rocks. That goes back into the piston to cylinder clearance.
 

·
Registered
Joined
·
2,317 Posts
Discussion Starter · #10 ·
Basically I have the same 57mm cylinder/kit that storminorman07 is working with but he us using a 4 vlave piston.....



The cylinder measures 56.8mm and the piston is only a 56mm...Wayy tooo much play...So i honed it out to fit a 57mm piston but by the time the deck height was correct I had too short of a chain.....(pin/deck height way too high) The top of pin to top of piston deck is 13mm.....The supplied piston is 10mm...So the piston is way too high....



Question? I have heard different opinions of the chain lengths changing cam timming, is this true? It seems as long as the ratio(crank/cam sprockets) is the same it would not matter what length chain was driving the cam.....



Does anyone know of a 57mm 13mm pin piston that has a 10mm from top of pin to top of piston/deck heighth?
 

·
Registered
Joined
·
8,623 Posts
TRT said:
Question? I have heard different opinions of the chain lengths changing cam timming, is this true? It seems as long as the ratio(crank/cam sprockets) is the same it would not matter what length chain was driving the cam.....


If you don't change anything, then as you shorten the cylinder you introduce more slack into the cam chain. The tensioner, acting on the upper half will press down more to take up the slack and mainain tension. This will cause the cam to roll backwards ever so slightly. Add enough slack, and you may go from spot on timing to half a tooth off.



How to fix? Slotted cam sprockets are one option. Or remove and re-press on the crank sprocket, rotating it forward enough to get the cam timing you want.
 

·
Registered
Joined
·
2,317 Posts
Discussion Starter · #16 ·
TRT said:
Question? I have heard different opinions of the chain lengths changing cam timming, is this true? It seems as long as the ratio(crank/cam sprockets) is the same it would not matter what length chain was driving the cam.....



Does anyone know of a 57mm 13mm pin piston that has a 10mm from top of pin to top of piston/deck heighth?


Thanks Kurlon...



Cycle what is your take on this?
 
G

·
A different length chain won't change the timing from rotation to rotation but if the total distance isn't setup right then it will be advanced or retarded when initially built. Slot the cam sprocket and degree the cam in when you assemble and it won't matter what you did.
 
1 - 17 of 17 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top