HELP Ring End Gap HELP

[gingrass179]

ok guys so since last February I have been sourcing parts and getting machining done slowly and surely...well I am now to the point of assembly and ring end gaps will be the purpose of this post

ok so this is an 87 6.9 block that was bored .040 over and that was just enough to get the taper out of the cylinders

the specs in my book say

6.9
top ring: .014-.024
2nd ring: .060-.070
oil control ring: .010-.024

7.3
top ring: .013-.045
2nd ring: .060-.085
oil control ring: not available (that's what it says in my Haynes Diesel techbook for the 5.7, 6.2 6.5GM and 6.9 and 7.3 Ford)

here are my ring end gap measurements

Cyl1
Top: .020
2nd: .078
Oil: .035

Cyl2
Top: .022
2nd: .077
Oil: .035

Cyl3
Top: .022
2nd: .080
Oil: .035

Cyl4
Top: .023
2nd: .078
Oil: .036

Cyl5
Top: .022
2nd: .079
Oil: .038

Cyl6
Top: .024
2nd: .077
Oil: .038

Cyl7
Top: .023
2nd: .080
Oil: .036

Cyl8
Top: .024
2nd: .078
Oil: .035

So obviously as seen here the top compression ring is at the top of its tolerance

the 2nd compression ring is about .010 more than spec

and the oil is also .010 more than spec

This stuff just came back from the machine shop how come nothing is adding up?

I have been reading and as cylinder size goes up ring end gap goes up...but how much extra ring end gap would I need by going up .040 in cylinder size?

also my mains are right at the top of there tolerances...

I have right at 5,000 into this engine so far between the balancing new bearings pistons rings head job cam injectors lifters pushrods head and main studs etc everything is new! so I don't want to take any chances with this thing..

Trying to see what the community thinks about these numbers

Thanks for any input guys!

 

[BDCarrillo]

I resort to the ring manufacturer recommendations when getting into bored over blocks and aftermarket parts. There are also preferences towards tighter/looser rings based on N/A vs turbo builds.

Kinda odd how you have variances between the first/second/oil rings. Typically a looser bore has a larger gap on all three rings. Are you pushing them in with an upside piston, or using a square down in the bore?

Also, the book specs may be aimed at evaluating used parts, not a fresh build.

Mel (Agnem) is working on crate 7.3s... May be useful to ask him what spec he's building them to.

 

[icanfixall]

The haynes book has not been the best to get tolerances or good information from. the factory manuals are much better. Maybe someone can post what is printed in that.

 

[IDIoit]

how are you checking the gap?

 

[BDCarrillo]

how are you checking the gap?

We're on the same track here...

 

[TahoeTom]

FWIW my manual shows 7.3 oil control ring gap at .008" to .030". This is for earlier 7.3s. The ring design changed with engine #598754. What brand pistons and rings? My Mahle rings were in spec for .030 oversize. Justin at R&D is doing a re-ring and bought another set to file fit the second ring. He thinks the gap spec on the second ring is too large.
http://www.ford-trucks.com/forums/1346590-racinndrummins-fullsize-bronco-idi-build-6.html

 

[IDIoit]

the proper way to check piston ring gap is to put 1 ring at a time, into the cylinder.
using the piston with a light coat of oil, push the piston ring 1/2 way with the piston itself so that it sits perfectly square, then feeler gauge the gap.

 

[gingrass179]

yes I checked the gaps properly with a good feeler gauge set...I individually set each top ring in each bore than brought them each down with an upside down piston/rod assembly til each piston head touched an oil squirter to make sure each ring was measure in the same spot... also did it up top to make sure the bore was plumb and got really close to the same readings...

 

[gingrass179]

what would a 6.9 .040 over be anyways? 7.1? cause its still in tolerance of a 7.3?

 

[laserjock]

I would go to the ring manufacturer specs if it's overbored that much. You are running oversize Pistons too right?

 

[gingrass179]

yes

 

[IDIoit]

ring gap is based solely on bore size to inch of gap
on my gassers, i use 0.004" per 1" of bore.
contact the ring manufacturer like lazerjock said.

 

[FarmerFrank]

IMO, I always file a little much. Built a 408 stroker Windsor once and broke piston tops TWO different times. After that I filled big and never had a problem breaking pistons. Just my .02 but if a few thousands bigger saves a rebuild I'm in.

 

[IDIoit]

it also depends on the type of induction youre running.
forced induction introduces more heat, you need larger clearances for expansion.

i apply extra ring gap to boat engines as well, they see most of their time at high RPM

 

[ironworker40]

The haynes book has not been the best to get tolerances or good information from. the factory manuals are much better. Maybe someone can post what is printed in that.

1987 ford manual states the same spec as op posted
top ring: .014-.024
2nd ring: .060-.070
oil control ring: .010-.024