Ring gap question

[beast02er]

I'm setting the ring gap on my new rings and have some issues that don't make sense to me. I bought +.25 oversize rings and was planning on filing them to size.

Weird thing is, I put them in the bore initially and the gap is around .028......so i'm wondering whats going on here. If i'm trying to hit .013-.014, then I can't do anything with these rings. What i'm wondering is why they weren't to where I had to file them.

Thanks,

[c.d.iesel]

either the bore measurement was off?

the rings miss packaged?

wrong rings ordered?

your method for measuring rig gap is off?

are inserting the ring in to the BOTTOM of the

bore and measuring as the photo below shows?

[oldguy]

either the bore measurement was off?

are inserting the ring in to the BOTTOM of the

bore and measuring as the photo below shows?

There is NO reason for measuring at the bottom of the cylinder. The rings dont even go down that far when they're on the piston. Put the ring in the top of the cylinder. Push it down an inch with a flat piston. Measure with feeler gauge. Done.

Unless this is some super performance race motor. Setting the ring gap is something some BS blueprinting book told you to do and you're doing alot of work for nothing. The bmw factory doesn't set the ring gap on any motor they make. It's always built into the ring construction.

You've either got the wrong rings. Or your bore measurement was way off. More likely the measurement as manufacturers are really really good at putting the right rings in the correct box. It's their job and they do it alot of times every day. Is this a freshly honed cylinder? What did the machinist say it was? did you buy these rings new from a part store or for $20 on some NOS leftover ebay sale? The gap measurement doesn't even make sense. Usually for every .001" oversize the hole gets. The ring gap goes up about .003". So if you got .010" oversize rings and your gap was .028 and it's supposed to be .013. That would look like a .015" oversize hole which isn't something you'd machine anything to. If you come back and say you took a block and just dingle berry honed it because you could "still see the crosshatch" and it "looked standard" you receive no more help.

[Harv]

I have never had to gap piston rings when building a motor. Every set I have ever installed has been spot on.

Maybe have the wrong rings?

John

[c.d.iesel]

....... "There is NO reason for measuring at the bottom of the cylinder"

wow man - whers da love ?

yer tone is not altogether warm and helpful

and i also won't tell you the secret to ring gaps,

and measuring at the bottom of the bore

[beast02er]

"wow man - whers da love ?

yer tone is not altogether warm and helpful "

Glad it's not just me that thought that! That's the great thing about this board above others out there, the information and help you can get. But, you still run in to the grumps that have to flame people for not check the search or posting something that's already posted.

I have another car which has NO US support forums (well, an old school dinosaur email type list), nothing as useful as this. It is nice if you are thumping your head (maybe staring at the answer but not knowing it) to pop on here and have someone help.

I think I figured out my ring issue, I was a bozo and ordered the wrong ones I believe.

-Bryan

[jgerock]

I guess I'm in the bottom rung of folks here with my tii engine. I used a "dingle-berry" ball hone to clean up my bores and re-ringed the 2nd oversize pistons to extend the life of my engine. I inserted the rings from the top and pushed them down about 2" into the bore to take measurements. All were OK (I purchased Goetze rings).

[beast02er]

Jim, i'm doing the same! Though I was a double dingle and ordered the wrong pistons.

How's the engine doing for you? I'm trying to salvage a bad engine build that I paid too much for apparently! Hopefully this will give me at least a few thousand more miles!

[jgerock]

Jim, i'm doing the same! Though I was a double dingle and ordered the wrong pistons.

How's the engine doing for you? I'm trying to salvage a bad engine build that I paid too much for apparently! Hopefully this will give me at least a few thousand more miles!

So far - the engine runs great and I'm getting about 33 mpg on long trips (still with the 4-speed tranny)! I installed a "turbo" head gasket with new head bolts. Last time I checked the compression, all (4) bores were almost 180 PSI (warm engine).

BTW - I purchased a 3.5" diameter ball hone, honing oil and a bore cleaning brush from Brush Research Company. Very good products.

[aa/fd]

I hate to break the news but measuring and preparing a proper engine build is not blueprinting BS from some book.

You should never install anything out of the box without a micrometer in your hand, I don't care who manufactures it.

Your hard earned money is worth the time to learn and do it right the first time.

[jgerock]

I hate to break the news but measuring and preparing a proper engine build is not blueprinting BS from some book.

You should never install anything out of the box without a micrometer in your hand, I don't care who manufactures it.

Your hard earned money is worth the time to learn and do it right the first time.

I agree 100% with your comments. My engine "work" was only done to extend the life of my original VIN block and head because of the loss in power and a poorly machined head by a PO. I did take my head and upper timing cover to a reputable machine shop for inspection, valve leakage testing and proper surfacing. All (4) pistons and rods were carefully cleaned (by me) before the new rings were installed (using a ring spreader). New rod bearings and an oil pump were also installed.

I am biding my time with this engine (the tii isn't a daily driver), then I'll have to find another one. The cylinder head is at the minimum thickness and the pistons are already 2nd oversize.

[oldguy]

I hate to break the news but measuring and preparing a proper engine build is not blueprinting BS from some book.

You should never install anything out of the box without a micrometer in your hand, I don't care who manufactures it.

Your hard earned money is worth the time to learn and do it right the first time.

I agree that a "proper engine" should have some blueprinting. Sorry if I came off harsh but there's no point in buying a set of rings.. setting the ring gaps etc on old worn bores with used pistons. If you understand the "why" behind setting ring gaps then you'll know that the previous two points make this an academic exercise.

Blueprinting is a highly suspect practice that "everyone does". What is blueprinted for you is not for another person. There is a cheap book on amazon about blueprinting called "step by step guide to engine blueprinting" by rick voegelin. There's 200 pages of measurements to take on an engine. If you want a "fully blueprinted" engine start at page 1 and finish the book. You'll probably be stuck in the middle trying to find a "good block" because the factory machining is always off a little. So certain flaws you accept that preclude other machining steps.

Also, using a tsnap and a digital caliper for bore measurements is good for figuring out if you've got a STD or a .020" over bore but it does nothing for telling you if you've got a .020 or a .021" bore. Unless you've got like 5-10 years of machinist experience working with tsnaps which most of those guys are old aircraft machinists. You don't have a good enough "feel" for them to get an accurate number. Then you throw a harbor freight digital caliper on top. Seeing that lets me know he doesn't have a proper micrometer set so then I know he didn't measure the piston for wear.

There's nothing wrong with this kind of a rebuild. A ring and bearing refresh. But there's no need to sweat on some of the minute details. In this thread you mentioned you bought +.25mm oversize rings and you're on your second overbore. That may be your problem. Did you buy .25mm rings larger than your bore (ie like .75mm)? or .25mm rings?

For others that read this thread. Please don't commit the same mistakes as a customer who called me last week.

"I measured the piston to wall clearance with a feeler gauge."

"I used a digital caliper to measure the piston"

He was convinced that std pistons in a .020" hole would work because the pistons he had didn't have alot of piston to wall clearance. He measured them and they were .010" over stock from the factory according to his caliper and he could only jam a .010" feeler gauge between the piston and wall. So he took them out of his old motor. Put them in his .020" over motor with .020" rings on them and it was making a helluva noise. Didn't know why. Asked me if he thought the rings could be made out of spec because it was the only thing he didn't measure.

[jgerock]

"Old Guy" - The original poster is a different person, but we are on a similar path with our "last-ditch" efforts. I am a degreed Mechanical Engineer and understand the logic behind proper engine building. In hindsight, after uncovering the issues with my engine, I would have delivered it to a reputable builder for proper engine work.

1) My digital caliper is an AmPro brand purchased from Advanced Auto Parts. Yes it is cheap but it worked for me.

2) I measured the piston diameters using the Blue book instructions.

3) I measured the side clearance of the original rings in the ring lands using the Blue Book instructions and feeler gauges. All were OK.

4) I measured the bore of each cylinder at (3) different heights and at multiple locations around the bore. The snap gauge was borrowed from a mechanic friend because I didn't have a direct-reading telescopic bore gauge.

5) The new rings were inserted into the bores and checked for end gap.

6) New rings installed on the pistons and staggered per the Blue Book instructions.

[Guest Anonymous]

I have never had to gap piston rings when building a motor. Every set I have ever installed has been spot on.

Maybe have the wrong rings?John

You must be plain lucky or work with perfect parts made for the Space program. When Pratt & Whitney and Curtiss Wright spent most of its efforts on reciprocating piston engines, ring gap was never left to chance. Too much at stake. We filed piston rings as needed, which is why there were machines designed specifically for that purpose.

Production standards have no doubt improved with laser technology, but even when dealing with fresh off the assembly line parts, cutting and pressing equipment wears and there are tolerances to consider. In a perfect world, every machine shop's boring and honing would result in identical measurements - but they don't (except according to Arkansans). The same is more true for most shadetree mechanics who undertake their own machining.

Who's to say my 80 year old Starrett micrometers are necessarily better than inexpensive asian digital equipment, if they both accurately measure the same dimensions. The digital readout might have helped my eyesight 40 years ago!

For youngsters, see what Deves piston rings says on the subject:

"Check the end gap of the compression rings by inserting them, one at a time, into the cylinder and squaring them to the cylinder wall by turning a piston upside down and pushing the ring down into the cylinder approximately one inch (with the top of the piston). Measure the end gap with a feeler gauge. Check this against the end gap spec chart at the back of the Deves Piston Ring catalog or the instruction sheet included in each set of rings. If the gaps are too small, the ends of the rings need to be filed. If the gaps are too large, you may have the wrong size rings, or your cylinder may be worn to the point that it needs to be bored and oversize pistons installed. But, if the cylinder is still within factory tolerances, it is possible to install oversize rings (.010"/ .025mm larger than the bore) and file the ends to the correct gap. Please call to check availability for your particular application.

Check each compression ring in the cylinder in which it will be installed. Keep the rings and cylinders consistent as there might be some variance in the individual cylinders and the rings are gapped per the cylinders. There is no need to check the end gaps on the Deves four-piece oil ring. The rails are made for specific bore sizes and are pre-gapped at the factory. Just make sure you have the correct set." http://www.deves.com/tips.cfm I am confident other ring makers provide similar advice to the public, whereas the trade is presumed to have this working knowledge.

There are many reputable engine builders. There are also many generally accepted practices each builder and designer uses to establish a base line for a reliable build. However, most highly regarded builders have their own closely guarded tricks and this includes piston ring design, measurements, and yes, modifications.

[jgerock]

I'll add another note to my "shade-tree" method. I purchased a ring file because I thought I would have to adjust the Goetz rings to fit the individual bores, but I must have been pretty lucky, because I didn't have to use it.

Old Guy: I'm jealous of your Starrett measurement devices. I remember using them in a machine shop class in college. As you well know, there is a trick to holding them for taking proper measurements (just like using a set of feeler gauges).