bore

[Mike Mayer]

I have a .0040 over bore on an 8ba I know this is basic but what is the bore in inches ? i am having a problem my pistons are very tight in the bore. I have to tap them to get them installed. I Really believe something is wrong.

 

[KiWinUS]

I believe you mean .040 oversize.
Bore would be 3.2275
Plus clearance

 

[flatjack9]

Typical clearance is around .002 for cast pistons.

 

[flatjack9]

Typical clearance is around .002 for cast pistons.

Clearance would be specified by manufacturer

 

[Mart]

Standard bore should be 3.1875. Based on this you can calculate any oversize.

Not being snarky but .040 over should be 3.2275. C'mon Kiwi, get with the programme!

Mart.

 

[Aarongriffey]

Are you tapping on the pistons to move them in the bore without the rings on them?

 

[Mike Mayer]

no with the rings

 

[KiWinUS]

Standard bore should be 3.1875. Based on this you can calculate any oversize.

Not being snarky but .040 over should be 3.2275. C'mon Kiwi, get with the programme!

Mart.

Oh ya got me Mart. I even wrote it on my scratch paper correct but fat fingered & didn’t proofread.

 

[hotrodart]

Try using a micrometer on the pistons and cylinders to determine the actual clearances. Also, you need to check the ring end gaps for proper clearances.

 

[Mike Mayer]

thank you all I now have all my ducks in a row I am not a kiwi but i am an Ohio Buckeye that is a useless nut.

 

[Ol' Ron]

End gap couls be an Issue. Install a ring and measure it should be around .016".
Gramps

 

[Flathead]

If you are using a three piece oil ring they have a fair amount of drag when new.

 

[Elmo Rodge]

Out of curiosity, are you using a ring compressor?
Wayno

 

[Ronnieroadster]

If you have checked for proper ring end gap the two compression and the one piece oil ring {I'm sure you did} then you may have a problem with the three piece oil ring. Its virtually impossible to check ring clearance on the three piece assembly. You can check the two steel oil rings from the assembly for gap but the expander cannot be checked. I have seen many times where the expander is actually to long. This will cause a very tight situation. I'm not saying that's what's happening however if you remove the three piece assembly and then try the piston again see what happens. Its worth a try.
Ronnieroadster

 

[Pete]

If you have checked for proper ring end gap the two compression and the one piece oil ring {I'm sure you did} then you may have a problem with the three piece oil ring. Its virtually impossible to check ring clearance on the three piece assembly. You can check the two steel oil rings from the assembly for gap but the expander cannot be checked. I have seen many times where the expander is actually to long. This will cause a very tight situation. I'm not saying that's what's happening however if you remove the three piece assembly and then try the piston again see what happens. Its worth a try.
Ronnieroadster

Another common problem is getting the ends of the expander overlapped instead of butted together.

 

[Mike Mayer]

I am using the three piece ring i have three types of ring compressers .
my favorite is a clamp type thanks to all of you you have no idea how much help you have been this is my last build I am having vision problems ,but with your help this one is becoming a special one . thank you again Chaplain Mike

 

[hotrodart]

I did not see anyone mention bearing clearances......check all rods (and rod side clearances) and mains for proper clearances.......too tight will give you a motor hard to rotate.