Piston Rings don´t fit, too little clearance, sits too tight

[bollerwagon]

Reassembling my Volvo Penta AQ271C after honing, the piston rings I purchased (Sealed Power Performance Piston Ring Sets E251K) don´t seem to fit. The piston is a GM piston p/n 10046106, I assume there are the original ones.

With this piston the oil scraper rings were too wide, the piston ring was not fitting into the groove completely and the piston could not be inserted into the cylinder.
Since on of the piston showed some wear, we decided to take new pistons. There the oil scraper rigs fitted fine.

But then we noticed, that the compression ring #2 would not fit into piston. The rings (#1 and #2) have a thickness of 1.89mm as they should have according to the manual. But the groove of the pistons was different. While #1 was fine, #2 sits way too tight. Clearance should be 0.03-0.11mm but on #2 it was basically zero. Weirdly same phenomenon shows on the old pistons.

So I am confused now and don´t know what to do.

 

[Lou C]

I'd say you probably should find a good automotive machine shop and get advice from them.

 

[alldodge]

But then we noticed, that the compression ring #2 would not fit into piston. The rings (#1 and #2) have a thickness of 1.89mm as they should have according to the manual. But the groove of the pistons was different. While #1 was fine, #2 sits way too tight. Clearance should be 0.03-0.11mm but on #2 it was basically zero. Weirdly same phenomenon shows on the old pistons.

Take #2 and place just the ring in the top of the bore and measure gap.

Use a piston without rings and push into bore about 10mm and measure gap

Repeat the gap measurement every 10 or so mm

 

[ESGWheel]

@bollerwagon

It seems that you have had issues with at least two of the types ring clearances thus a suggestion to make sure it’s understood. While you are aware of these critical clearances, I only highlight them here for the clarity of the discussion and for others to understand.

Piston Ring Gap Clearance: this is the space between the two ends of the ring when the ring is in the cylinder bore. I may have misinterpreted but it seems that this was the first issue with the Oil Rings in the original pistons.

Piston Ring Side Clearance: this deals with the thickness of the ring and the width of the groove in the poison. This seems to be your current issue with the new pistons.

There is also a Back Clearance but not getting into that. See picture below for all these clearances.

Now as to your current issue, assuming its is Ring Side Clearance and how is this possible with new parts I can only offer this: they just do not make it they way they used to. This is not meant to be snide remark to frustrate you but rather one I have experienced. Also I am a fan Dave’s Auto Center videos (link) and lately he has become more vocal about the crap that is out there including from the OEMs.

Which I guess does lead to, as Lou suggests, go to a quality auto machine shop. Suggest seeing if there is a “speed shop” in your area > they will know the best machine shops around and may be able to take point on getting it fixed.

If the issue is one of Ring Gap, then the process outlined by AllDodge is the way to go, as I am sure you know you can adjust this gap yourself (carefully).

Good luck and keep posting on how it goes.

 

[Scott Danforth]

You have to file fit rings to get the gap you need. It's engine building 101.

 

[ESGWheel]

You have to file fit rings to get the gap you need. It's engine building 101.

Yes of course
But i think the OP's current issue is Side and not Gap clearance....

 

[Scott Danforth]

Yes of course
But i think the OP's current issue is Side and not Gap clearance....

Oops, lack of coffee this morning and sort of skimmed ADs answer


The AQ271C is a 37 year old motor. Basically a 1987-1989 GM 350.

Mehling was one of 3 or 4 supplies back then to GM. Not sure about Sealed Power which is mostly after market . Sealed power back in the late 80s was it's own company when the engine was first assembled

Sealed power has gone through a few different owners since then. Sealed Power became SPX, then became a federal mogul brand with the rings currently being made at UPI under license Prior to UPI it was MPR when the plant went joint venture

I believe the piston is this assembly that may have any of the following piston castings (pulled from an old link(

12361371 High Performance Piston
This piston is for 350-300 and 330 HP service with SP I.D. This 350 standard, pressed pin, high performance piston has a 9.1:1 compression ratio with 64cc head chamber volume (casting ID#10046106, 14075651 or 14093679)."

 

[bollerwagon]

Thank you all so far, let me be more percise on the problem. It indeed is the Piston Ring Side Clearance. On the first attempt, when trying to fit the oil scraper rings on the 10046106 pistons, there indeed was back clearance issues. Since one piston was a bit worn and my workshop hat some new pistons on hand, we chose to use new ones.
The E251K rings #1 and #2 have both 1.98mm, that is exactly what the workshop manual from Volvo Penta says they should have.
But the pistons seem to have different groove heights, that is what I don´t understand. The ones that were in the engine (I assume these were original), also the new replacement pistons. So this is why clearance on ring #1 is fine, but #2 sits too tight.

 

[Scott Danforth]

The E251K rings #1 and #2 have both 1.98mm, that is exactly what the workshop manual from Volvo Penta says they should have.

Volvo bought the long block from GM. GM had a few different sources for the piston assembly. There could have been a change.

Are these new rings for old pistons?

 

[bollerwagon]

The parts list shows two different types of pistons, depending on the block (Std S4 and Std S5). But the rings are the same, as it seems.

 

[bollerwagon]

Are these new rings for old pistons?

Yes, brand new set of piston rings that are supposed to work with these pistons.

 

[Ptr.Torch]

I think your best (not cheapest in the short term) option is to buy both piston and rings from same source to ensure a proper fit. Then check end clearence to be sure. Also - align rings so the gaps are 180 degrees away from the next as they sit on the piston before installing them. That ensures the lest possible amount of blow-by once the rings have been broken in and seated.

 

[ESGWheel]

For my benefit here is a recap of your situation > it helps me think thru things

• Doing a rebuild on engine > only honing cylinders, not bored
• Intending to reuse ‘old’ pistons but with all new rings had back-clearance issue on Oil scrapper
• Thus, decided to go with New Pistons that the shop had on the shelf (*)
• Using same new ring set (E251K) found the all the rings (Compression and Wiper (#1 & #2) to be the correct thickness and as per spec.
• However, while Compression ring will fit into piston groove with proper clearance, the Wiper ring does not. This is true for all 4 new pistons > All 4 pistons have Side Clearance issues with the Wiper ring. More: that all 4 new pistons are the same visually including the narrower Wiper ring groove.

I asterisked the new pistons from the shop to highlight that they may not what you think they are. While others will know better, I too find it odd that they would be different sized grooves.

So, what to do? Choices exist and depends on “how tight” that wiper ring is in the groove. Here is my assessment in order of priority with No. 1 being ‘best choice’ IMO.

1. Return the shop pistons and get proper new ones
2. Get the rings that are made for these pistons.
3. Lap the wiper rings to fit

Lapping can be done but needs to be done correctly and carefully but do not expect to be taking several thou off using this process, hence the ‘how tight’ comment.

My justification for no. 1 is this: you are already heavily invested in this rebuild and if the shop is willing to take the pistons back your out of pocket is much less. And always best to do it by the book vs. making it work.

Keep asking and posting and good luck!

 

[cyclops222]

There is very little quality companies left . The unseen buyers up of good companies. Cheapen the critical tolerances of ALL machined parts.
You have NO CONFIDENCE in what you are buying. WEB or even local place.
Heck You can get not accurate Micrometer or caliper.

 

[Mc Tool]

There is very little quality companies left . The unseen buyers up of good companies. Cheapen the critical tolerances of ALL machined parts.
You have NO CONFIDENCE in what you are buying. WEB or even local place.
Heck You can get not accurate Micrometer or caliper.

Talk about glass half empty cyclops , how do you get out of bed every day ? Yeah , you must be a blast at parties .

 

[Scott Danforth]

If you bought pistons from a shop, have them supply the rings

 

[Scott Danforth]

Yes, brand new set of piston rings that are supposed to work with these pistons.

Did you mix the skirts to make sure they did not collapse?

Did you use a bore gauge to make sure the birds are not tapered?

Never been able to just replace rings. Usually a 0.020 bore and hone needed as a minimum

 

[bollerwagon]

All cylinder values were within tolerances, so we only replaced bearings. (The engine should not have been taken apart in the frst place, but back then I knew nothing and did how I was told.)
Pistons also new because one skirt showed some wear and I could not find a better single replacement piston in time.
He now grinded a tiny bit out of the second gap and rings fit well.

Next problem: the valve guides are too loose, valves wiggle a lot. Seems like Volvo Penta used thicker valves than standard, according to the workshop manual the valve stern diameter is 9.45 mm (0.372 in). Would you take oversize valves as in the workshop manual, or use Valve Guide Liners?

 

[Scott Danforth]

I would swap the heads from the current heads you have to vortec heads and pick up another 30+ hp

 

[alldodge]

Next problem: the valve guides are too loose, valves wiggle a lot. Seems like Volvo Penta used thicker valves than standard, according to the workshop manual the valve stern diameter is 9.45 mm (0.372 in). Would you take oversize valves as in the workshop manual, or use Valve Guide Liners?

If not replacing the heads replace the guides