Thread: ring gap questions

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I'm rebuilding a 1973 B-20 4 cylinder push rod Volvo motor that was bored .030 over. Tough as nails old "tractor" motor- no overhead cam shafts or timing belts or aluminum heads to corrode- just good old cast iron.

I just got the block back from the machine shop with new cam bearings and hot tanked. Rods were checked and didn't need new wrist pin bushings
everything is looking good.

so today I cleaned all the engine parts---installed the pistons on the rods
and started checking the pistons/rings
Deves rings
after reading the installation sheet that came with the rings
I was measuring the fit of the top ring in the piston and I could not get .006 to fit between the ring and ring groove so that piston was still good .

Then I noticed that the ring is the same size as the top of the piston seems to me that the ring should be bigger diameter
It was too late to call the parts place tonight-
my piston tops are 89.5mm(little more than 3 1/2") and the rings are 90mm
there is almost a 1/2" gap on the rings uninstalled

I'm pretty sure that they sent us the wrong piston rings-

anybody know the correct ring gap for that size of piston 89.5mm or 3 1/2"
I'm sort of remembering that it is .004 for each inch of piston does that sound about right
.004 x 3.5= .014 ring gap

How can I figure what size rings to order I've already told the parts place the piston size and maybe they just messed up and sent the wrong ring

spiritual advice welcomed
thanks
hank

Take 'em back. They screwed up.

Originally Posted by TOW'D

I'm rebuilding a 1973 B-20 4 cylinder push rod Volvo motor that was bored .030 over. Tough as nails old "tractor" motor- no overhead cam shafts or timing belts or aluminum heads to corrode- just good old cast iron.

I just got the block back from the machine shop with new cam bearings and hot tanked. Rods were checked and didn't need new wrist pin bushings
everything is looking good.

so today I cleaned all the engine parts---installed the pistons on the rods
and started checking the pistons/rings
Deves rings
after reading the installation sheet that came with the rings
I was measuring the fit of the top ring in the piston and I could not get .006 to fit between the ring and ring groove so that piston was still good .

Then I noticed that the ring is the same size as the top of the piston seems to me that the ring should be bigger diameter
It was too late to call the parts place tonight-
my piston tops are 89.5mm(little more than 3 1/2") and the rings are 90mm
there is almost a 1/2" gap on the rings uninstalled

I'm pretty sure that they sent us the wrong piston rings-

anybody know the correct ring gap for that size of piston 89.5mm or 3 1/2"
I'm sort of remembering that it is .004 for each inch of piston does that sound about right
.004 x 3.5= .014 ring gap

How can I figure what size rings to order I've already told the parts place the piston size and maybe they just messed up and sent the wrong ring

spiritual advice welcomed
thanks
hank

Ring gap is based on application.
Street,strip,drag,nitrous applications, blown applications,circle track etc.
Bottom line is you have the wrong rings.

are you trying to put stock bore pistons in a bored block ? you didn`t mention you had new oversized pistons or not

look at the piston ring box see if it says STD. or .030 anywhere on it. but since its bored .030 over your going to need .030 over rings and .030 over pistons. and denny has posted the right way to check your ring gap but otherwise the way you checked it you should get anywhere from .002 - .005 for checking the ring groove. I would think there would be some sort of specs & instructions with the rings but i could be wrong.

The engine was rebuilt in the '90 and has just sat after a accident
The pistons are .030 over
I'm just refreshing it up for use in our VW 4x4 syncro Vanagon
I'll put the rings in the bore but pretty sure they are wrong
thanks for the input

update on my rings

I received the correct size of rings yesterday for our rebuild- The package said the rings were made on Jan 28 2008- nice having fresh ring to work with instead of "old" stock-

They fit into the bore with only .002 gap and I'll have to file them to get the correct gap-
The motor is NA fuel injected so nothing too wild about it
what would better to shoot for when doing the filing of the ring gap
.010 to .018 is what the paper that came with the rings showed.
should we just go for right in between them say .014

thanks
hank

I use the rule of thumb...0.0045" for each inch of bore (4.000" bore, 0.018" gap) with conventional cast pistons. Hypereutectics require more gap and use a factor beginning at 0.0065" for each inch of bore for naturally aspirated street motors.
http://www.kb-silvolite.com/download...Automotive.pdf

I got .016 to .022 from a Volvo site for the ring gap
and filed the rings so I have a .020 gap
read in 3 different places in each cylinder
looks good to me so far

Tomorrow I'm taking the piston/rod assemblies to a grocery store that a buddy runs to weigh them.
Just to see how close they are.

thanks for the help