Clipping oil ring expanders for reduced tension?

[KnightEngines]

As a follow on from the thread I posted last week about low tension thin top rings with gas ported spacers for a restricted class road race engine -
I've got another one from the same class in for a freshen, it's an engine I build a couple of years ago & has been a good one, but it's owner is lower budget, not a contender for the title & I gotta get it back together before I can source the new style rings.

As a part way measure I wondered about just clipping the oil ring expanders to drop the oil ring tension a little, but I've never done it & wouldn't have a clue where to start.

What's the procedure for this & how can you check tension?

[pamotorman]

never did a auto engine but have done 5 HP briggs for go kart racing. used a ohaus pull scale to pull the piston in the bore and reduced the pull reading by 25% by clipping the expander. I am sure you could do the same with an auto engine. put the piston in upside down and attach the scale to the wrist pin. https://www.globalscientificsupply.com/ ... Ak-B8P8HAQ

[Barry_R]

Grab a drill bit about .010 smaller than the radius of the humps in the expander. Use a pair of pliers to squeeze every third or fourth hump around the drill bit.

[benno318]

i do it all the time for the same( presumably) hq engine class. what sort of expander are you working with, an old acl type??

i grind (and it takes just a very small amount to make a difference) then measure, grind and measure - wire buff after each grind of course - fit oil ring assy to an inverted piston with pin in the bore, attached to spring fish scale - very low tech but measurable results. i have gone about 8-9 lb constant pull with no massive oil use or smoke etc, aim for 10-12 these days just because, also i think the 2nd rings i use are very good at controlling oil.

can do the same with the grant type expander with the little wire going through joining the ends but theyre thinner and more fragile, obviously will grind quicker. no matter which expander you are doing, we are talking maybe 10-20 thou off one end at a time here so please trial and error it with an old one first!!

enjoy!

[BOOT]

What is the downside to this mod? Never herd of this, so did a quick search and one person suggest using a size under. So I suppose if it was an el-cheapo slap together build you would buy two sets of rings n use standard size in maybe a .030 bore?

[engineguyBill]

It is very hard (ne: impossible) to get all of the oil rings consistant when tweaking the expanders. Several ring manufacturers offer oil ring assemblies with different tension ranges and some of them offer the oil rings separately and this is the best way to go. When ring manufacturers design different oil ring tensions, they often also use rails with different radial thickness to arrive at the specified tension.
As far as checking oil ring assembly tension goes, the ol' fish scale method is surprisingly accurate. Oil ring tension is checked at ring factories using expensive test fixtures that are designed specifically for this use.

[Truckedup]

How much power is the engine seeing from this modification?

[benno318]

What is the downside to this mod? Never herd of this, so did a quick search and one person suggest using a size under. So I suppose if it was an el-cheapo slap together build you would buy two sets of rings n use standard size in maybe a .030 bore?

the std size probably wouldnt even contact the bores! you MIGHT go 010 under - ie use .020 in a .030 bore, this i have done before.

not sure on power figures with dead accuracy, but from many years of testing and tuning with chassis dyno's i can estimate about 1% increase at our meager outputs of 135 rwhp

[KnightEngines]

Fish scale on the shopping list, thanks guys.

[vortecpro]

I run down to 7 lbs on the stockers, I can turn the short block over by the crank flange by hand.

[vortecpro]

I run down to 7 lbs on the stockers, I can turn the short block over by the crank flange by hand.

[randy331]

the std size probably wouldnt even contact the bores! you MIGHT go 010 under - ie use .020 in a .030 bore, this i have done before.

I know one sbc that's 4.040" bore with 4.00 expander under the 4.040" oil rails.

No vacuum and no smoke. Very good engine for what it is.

It has napier second and from what I've seen that helps with what you can get away with on oil rails.

It also has 4032 material pistons and the bottom of the skirts are modified in a manner that should help oil load at the rings.

Randy

[CGT]

Grab a drill bit about .010 smaller than the radius of the humps in the expander. Use a pair of pliers to squeeze every third or fourth hump around the drill bit.

That's a good idea. Its hard to keep them consistent "free handing" it. Nice tip, although I have been just playing with smaller expanders.

I know one sbc that's 4.040" bore with 4.00 expander under the 4.040" oil rails.

I think they may be 4.005. I'd have to look at the notes. I tried quite a few different expanders in there.

No vacuum and no smoke. Very good engine for what it is.

5.5lbs rotating, no smoke......yet. Hopefully it will soon be an even better engine. It will be cool to see what effect some vacuum has on it......and some dyno's on 87 octane?

[KnightEngines]

Checked the rings out the box with a light coat of WD40/trans fluid mix on the bores.
Oil ring alone was 24lb on the fish scale to move it.

Ground the ends of the expanders on the side of the valve facer wheel & got it down to 13-15lb, not keen to push it further yet, we'll see how it goes at that.

It made a huge difference to the effort required to turn the motor over, I have no doubt she'll pick up some HP.

Motor is getting sealed/inspected tonight, then it can go back in the car.

Not going to be a true back to back as I also lightened the valve spring retainers 10g & did some minor grey area shenanigans with the valve train - but from past experience that won't make more actual hp, just extend the top end a couple of hundred rpm.

[BlitzA64]

Very cool, a little back yard sneakiness