Piston rings

[SpitfireBGT]

Oh wise ones

I'm installing .40 over AE Hepolite pistons in my freshly bored block. The top and middle rings aren't the same. As installed right out of the box the top rings are chamfered slightly top and bottom. The second ring is square. Can I assume they were shipped in the orientation that they should be installed? Or should the chamfered ring be on the bottom and square on top?

Also what is the opinion on what the ring gaps should be top and bottom? My machinist recommends .012 for the top and .014 for the bottom.

Thanks

Mike

[Nick Jones]

Don't think I've ever received pistons with the rings already fitted.  It's not helpful as you have to take them off to check the gaps.  I wouldn't really agrue with you machinist, except that I seem to remember being told that if anything the top ring has the bigger gap as it gets hotter.....

https://www.fagengine.com/blogs/tech/hepolite-piston-ring-installation-notes#:~:text=RING GAP MUST BE CHECKED,no sharp edges are present.

This any use?  There's also a  pdf doc if you scroll down a little

[SpitfireBGT]

Hmmm I bought these at a swap meet in their original packaging. The box doesn't really have a place to hold the rings separately from the pistons. 

I found this on the web Performance Piston Rings - Engine Builder Magazine

It says that the chamfered rings should be on top. It is curious that the rings have no markings for top or bottom. I'm going to install them as they are after gapping them. whatever that gap may be. More research ahead of me

[JumpingFrog]

Are all the compression rings plain iron? If one of the compression rings is chromed that will definitely be the top one.

I remember having a chart somewhere for this, but can't find it now...

Edit:
Here's a chart from the Herald/Spitfire/Vitesse workshop manual, suggesting parallel would go at the top. But I assume by chamfered, you don't mean a tapered ring? I suppose there must be some logic to it?

Edited February 17, 2024 by JumpingFrog

[SpitfireBGT]

Thanks Frog and Nick

Well that drawing confuses things a bit. But I dug out my old pistons and a magnifying glass. They have the beveled rings on top and the square ones on top. So that's the way I will install the new ones. 

My gaps are a little bigger than I would like. .015 for the top and .017 for the bottom. Will I get a lot of blowby with those gaps or should I just go with them? Better too big than too small I reckon.

[Nick Jones]

I wouldn’t fuss with those gaps. The only way to improve will be to buy a set of rings for the next undersize, which will then need lots of fettling to get them right.

Too big is definitely better than too small as too small risks them butting up the first time the engine gets properly hot and that tends to break them.

[Escadrille Ecosse]

7 hours ago, SpitfireBGT said:

Thanks Frog and Nick

Well that drawing confuses things a bit. But I dug out my old pistons and a magnifying glass. They have the beveled rings on top and the square ones on top. So that's the way I will install the new ones. 

My gaps are a little bigger than I would like. .015 for the top and .017 for the bottom. Will I get a lot of blowby with those gaps or should I just go with them? Better too big than too small I reckon.

Jumping Frog is correct. The drawing shows the correct way to fit the rings. If your old pistons are different then I would suggest that they are wrong.

Here is another drawing

The top compression ring should be chrome (although may look black) and have a SMALL bevel top and bottom. This is the one that does most of the work against engine compression

The second ring is the scraper ring and as the name suggests is there to scrape excess oil back down the bore. Which is why they are tapered as shown in the drawing.

The bottom oil control ring is there to manage lubricating oil for the bores in the 'goldilocks' zone.

The rings themeselves should have an identification for which way up they go in the groove. Usually it is a small dimple next to the ring gap. This goes on the upper face of the ring.

Remember to orient the ring gaps at near 120 degrees as possible and avoid any gaps being at the thrust faces of the piston (ie front and back) or directly above the gudgeon pin.

[SpitfireBGT]

Colin

Your pic is the opposite of frogs. But it is the same as my old pistons and the way my new pistons were shipped. So that is the way I'm putting them in. Small bevel on both sides on the top. Square in the middle. That seems to be the way all my research says to do it. They all look the same color.

Wish me luck

Mike

[JohnD]

Colin is very clear and correct, except for...

Rings spin in their grooves, at about 1000th of the rev rate, and they don't do so at exactly the same speed, so after a few minutes of running they are in random relative positions.    No point in careful positioning of ring gaps on installation.

John

[Escadrille Ecosse]

5 hours ago, SpitfireBGT said:

Colin

Your pic is the opposite of frogs. But it is the same as my old pistons and the way my new pistons were shipped. So that is the way I'm putting them in. Small bevel on both sides on the top. Square in the middle. That seems to be the way all my research says to do it. They all look the same color.

Wish me luck

Mike

Good luck Mike .

It'll be fine. 

4 minutes ago, JohnD said:

Colin is very clear and correct, except for...

Rings spin in their grooves, at about 1000th of the rev rate, and they don't do so at exactly the same speed, so after a few minutes of running they are in random relative positions.    No point in careful positioning of ring gaps on installation.

John

Agree about ring precession John, although it is rather more complicated than a simple 1/1000 of engine rpm and depends on speed, load and ring position. For example...

https://www.highpowermedia.com/Archive/rotation-of-piston-rings

However, all that aside the most critical time in the life of the rings and bores is that first startup before everything has run itself in. So I would still recommend assembling things in the best way possible as then you have done everything you can to get a good result. It costs nothing and is guaranteed not to make things worse. So just do it this way. 

 

[JumpingFrog]

7 hours ago, SpitfireBGT said:

Your pic is the opposite of frogs. But it is the same as my old pistons and the way my new pistons were shipped. So that is the way I'm putting them in. Small bevel on both sides on the top. Square in the middle. That seems to be the way all my research says to do it. They all look the same color.

I think both diagrams are showing the same thing, just from different eras. E.g. D-shaped cross-section rings are an improvement over earlier square rings.

Maybe the ring you said was square is actually slightly tapered/trapezoid/bevelled?

Edited February 20, 2024 by JumpingFrog

[JohnD]

Each to their own!

Two strokes,  because they pump both ways, and usually only have two rings, commonly have pinned rings, so that they don't rotate et all.  EG:

Edited February 20, 2024 by JohnD

[SpitfireBGT]

AHHHHHH

So which way should they go???

D shaped on top and slightly tapered on the bottom?????? as in Escadrille's drawing????

I was hoping to put it together this weekend but now you've got me paranoid about how they go

[SpitfireBGT]

Right

So how do you recommend It be run in?? 

My plan is to build oil pressure without plugs, start it and get it up to temperature, re torque the head, then drive it like my Mum between 2,000 and 4,000 Rpm for a couple hundred miles, change oil and filter then enjoy my zippy little car.   I'm sure that there is more to it than that.

[andymcp]

I guess it depends if your mum is Miss Daisy or Michelle Mouton...?  

[Escadrille Ecosse]

7 hours ago, SpitfireBGT said:

AHHHHHH

So which way should they go???

D shaped on top and slightly tapered on the bottom?????? as in Escadrille's drawing????

I was hoping to put it together this weekend but now you've got me paranoid about how they go

Basically yes. Both Jumping Frog and I are really saying the same thing. Just my drawing is slightly clearer.

I assume the bores have been honed or glaze busted for the new rings. If not this must be done first.

As for running in. Like you say. Build oil pressure with the plugs out then start it and keep the revs up around 2000 for 15-20 minutes to get things bedded in.

Do not let it idle during this period. Stop and restart if necessary for any reason.

Then drive it moderately until the first oil change gradually increasing the revs. I go with 300 to 500 miles.

Main thing here is actually more about not running the engine at high load. No low revs, big throttle opening.

in other words no pootling around at 25 mph in top or booting it at gear changes.