.01 Ring with Standard Piston

[Trnelson]

A little background.  I picked up my 71 240 last summer for a new hobby.  It is not a DD, race car or show car in the near future.  One of the reasons I bought it was to do a complete tear down and assembly on a fairly simple engine.  I pulled the motor and have torn down, cleaned, re-finished most all parts and I'm ready to re-assemble.  I have learned a lot and have a much more through understanding of how the engine works and how modifications impact all aspects of performance.  Knowing what I know now I do want to eventually have the block and head professionally machined with all new or machined components.  However, at this point in my new hobby I've about hit my spending limit for the short term. I ordered standard rings and bearings for the refresh and I am .003”out of tolerance on the rings. I know that for the best result and long term reliability the head and block should go to a machine shop.  My question is:   knowing that the car will only see 2-3,000 miles per year, with plans for a full on rebuild within 2 years would it be best to use the standard rings knowing that there will be some compression loss and blow by, probably about the same as before, or is it possible or make sense to pick up a set of .01 over rings and file them to fit within the .030- .045 spec.  There is no ridge at the top of the bore and the .003”out seems to be consistent  from top of the stroke to the bottom indicating very little if any taper.  I would like to see some improvement from all my efforts but absolutely do not want to create headaches down the road.  

 

 

 

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Thanks for the input

 

Tom

Edited January 13, 2021 by Trnelson

[Zed Head]

26 minutes ago, Trnelson said:

I ordered standard rings and bearings for the refresh and I am .003mm out of tolerance on the rings.

 

26 minutes ago, Trnelson said:

pick up a set of .01 over rings and file them to fit within the .030- .045 spec

What do you mean by "out of tolerance"?  End gap?  And do you really mean .003 millimeters?  That is a tenth of a thousandth of an inch. .0001 inches.

Is the bore oval'ed?  That's the other measurement you want to take.  

If you're only planning a few thousand miles on it you might be best to buy rings that will seat quickly.  Some ring materials would probably still be breaking in by the time you rebuild it again.  And I think that there are tricks to get a quick break-in, at the expense of longevity.  A rough hone finish, for example.  Not an expert, others know more.

[Trnelson]

I edited the original post to reflect inches not mm, my mistake. Yes, I am referring to the ring end gap. I’ll need to check on how oval’ed they are. Interesting thought on quicker break-in procedures, I’ll do some research on that. 
 

Thanks

[siteunseen]

I used cast iron rings with a quick/rough hone on my 2.8 block. My machinist and the internet instructed me to do down hill lower gear foot off the pedal. It sucks the rings to the cylinder walls for faster seating of the rings. The other is up and down rpms for short amounts of time, nothing steady too long. That car runs great and had solid numbers on all 6 when I did a compression check years ago. 165 I think?

On my 2.4 I used chrome faced moly rings with a specific hone for those rings. 83mm rings are hard to find without spending big bucks so I got Hastings from my machinist. I've never checked the compression on that motor but it runs so good I don't want to. 

I would stop by and talk to a machinist, they don't like talking on the phone, it's a waste of time for them. Machine work on these L motors is very basic, not too expensive. You need to find an older shop. They quit making these in 1984 but an older guy will say he's worked on thousands and would have to remember what to do. My best advice, if you haven't already got it, would be buy this book and read it 3 or 4 times. I was able to to rebuild mine without knowing anything about car motors.

https://www.amazon.com/gp/product/1931128030/ref=dbs_a_def_rwt_hsch_vapi_tpbk_p1_i3

 

[jonbill]

is your current ring end gap 0.049"? thats 1.2mm, which is very big. 

my recollection of the spec is around 0.3 to 0.4mm for the top ring. 

[siteunseen]

http://www.kangamotorsports.com/blog/setting-ring-gaps

 

Piston and piston ring manufacturers provide specification for their ring gaps dependent on the performance application. These are normally specified as a gap times by the cylinder bore diameter.

For our high performance street applications these were our values:

• Top Ring = Bore x 0.0045 = 3.4855 x 0.0045 = 0.0157 inches

• Second Ring = Bore x 0.0050 = 3.4855 x 0.0050 = 0.0174 inches

• Oil Ring > 0.015 inches

Given that we can only measure to 0.001 inches with our feeler gauges we rounded up or down the values to:

• Top Ring = 0.016 inches

• Second Ring = 0.017 inches*

• Oil Ring > 0.015 inches

[siteunseen]

29 minutes ago, jonbill said:

is your current ring end gap 0.049"? thats 1.2mm, which is very big. 

my recollection of the spec is around 0.3 to 0.4mm for the top ring. 

3.4855. That's a darn good recollection. 

[Trnelson]

My amateur strips are showing!  Took some more measurements this afternoon. So with the new standard rings installed to a depth of 2.5” I’m getting anywhere from .48mm to .53mm end gap. Monroe’s Manual says anything over .43mm get new rings. I understand that with this much discrepancy I will have to bore it out to get it right. My long term plan is to do a complete high quality, comprehensive build and now that I’m learning more about how everything works I’d like to take the time to figure out exactly what I want and how to get there. 
My question is has anyone tried a .01” oversized ring, filed down and used short term to make up for the worn items without causing any severe damage. I know that it used to be fairly common practice to get a “plus 10” ring job as a stop gap measure, I just haven’t found anything on anyone doing it on these motors. 

I realize it seems stupid to be this far in and not “go all the way” but this is my trial run project and I’ve already overshot the runway on expenses for the short term. The next go around will be much easier as I have most all of the tools and more experience to make educated decisions.   I’m really enjoying the process and look forward to building one without cutting any corners.  
@siteunseen I do have the book and it’s a great resource for sure. One issue I do have is that I live in the middle of nowhere and there are no quality machine shops within 1.5 hours from me. 

[siteunseen]

If it says anything over .43 get new rings I'm not thinking you should bore the cylinders, just get new rings. Maybe I'm not understanding but that's not unusual so I apologize if I'm simplifying too much. You think you live in the middle of nowhere!  I have one machine shop and one machinist. His brother does exhaust work.

Anyhow, don't do like I did and over think yourself to pieces. These are simple compared to most motors and you have a lot of guys just waiting to help here. It's cold out and we are sick of the news on television. PLEASE give me something Z related to talk about! 

[Zed Head]

The first thing that I'd do is to stop mixing your measurement systems together.  Pick metric or pick standard but pick just one.

What size are the pistons?  Rings, pistons and cylinders all need to work together.

I'd try one of the oversize rings, fit it, and see how it fits the bore.  If your bore is ovalized (you never answered that question) then it's probably equally bad to use an oversize ring gapped down as a "proper" ring with a big gap.  They're both round rings in oval bores.  Most of the blowby will come from the poor seal in general, not the larger gap.

You might just fit one oversize ring, stick it in the bore and shine a bright light around the edges.  If it's a poor fit you'll see light shining through.

[Trnelson]

Those are the measurements from new standard size rings.  Wondering if .01 over rings would be a feasible option to take up the slack short term. 
Trust me, I’m isolated in the mountains!  I see you’re in Bama my family is from Anniston which is considered HUGE compared to my current location!  Highlands, NC pop 968

[siteunseen]

Okay, you got me now.

If Anniston is considered huge you are isolated.