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914World.com _ 914World Garage _ Ring Gap

Posted by: swood Sep 1 2003, 02:18 PM

KB - 96mm pistons and stock overbored steel barrels. I'm getting ready to ring the pistons and check/set the gap. I believe the gap should be about .006", but can't remember and can't perform a search for some reason (some virus has dissed me).

I placed a ring in the top of the barrel and the gap was around .021". That's a bit over .006". Am I measuring it the right way? I measured my pistons and yes they are 96mm. Of course I 'll second guess myself and check again.

Thanks dudes.

Wow, post #100! I'm getting up there!

Posted by: Brad Roberts Sep 2 2003, 12:58 AM

You need to check the rings about 10mm down from the top (you may know this already) I also check them about midway down in the bore. .006 is fine for the street (other will chime in if it isnt).

I'm happy that your checking them..

B

Posted by: Racer Chris Sep 2 2003, 02:53 AM

3-4 thousandths per inch of bore is close for the compresson rings. I think 6 is too small and 21 too big.

Posted by: porsche735 Sep 2 2003, 01:25 PM

There is a spec in the Haynes manual. Something like a range of .012 to .024. I just did mine yesterday and they measured .016. .006 seems way too tight. A little heat and they are touching....

Chris

Posted by: Brad Roberts Sep 2 2003, 01:28 PM

So.. .020 should be fine. Gap them. Now I need to check the rings on the stock 2.0 Mahles I have.

Why does 6 sound familiar ? hum.

B

Posted by: porsche735 Sep 2 2003, 02:37 PM

I used a gauge and set the ring at about 1" down from the top of the cylinder. We checked it and got .016. We then flipped it over and checked about 2.5" from the bottom. This also measured .016. We did as Brad recommended and checked the top and the bottom of the swept path. All seems well.
Also, we cced our heads and found that there was a 2 cc variation across them all. We varied the shim thickness to account for this difference. By the way, the calculator on the PP page is messed up on the botom section. Just plug in your variables and use the top portion (not the extra shim to get what you want part).
After it is all said and done, we have matched CRs in all cylinders. Takes a while....

chris

Posted by: porsche735 Sep 2 2003, 02:46 PM

Hmmm, maybe I should set my valves to .020" and my rings to .006". I should get higher compression......

Posted by: Jake Raby Sep 2 2003, 03:46 PM

What rings do you have??? Pistons? Some of the pistons nowdays want 2 different gaps for each compression ring.

I install mine square in the cylinder and put them in the oven and see what you have and work from there...400 degrees is a good setting.

What is the application for the engine? hih revs and high oil temps demand different settings. Skirt clearance also makes a huge difference as well.

Posted by: swood Sep 2 2003, 07:45 PM

Jake: stock 1.8 jugs overbored to 96mm, 96mm KB hyperblahblahsomething. Hastings rings. Street driving, fast street driving when applicable.

If it matters I put in a modified T1 Schedek oil pump.

Posted by: swood Sep 2 2003, 11:08 PM

Got some more measurments, but I think I may take it to someone with some more sophisticated tools to double check.

Cylinder bore top and bottom - 3.78" = 96.012mm
Ring gap 1" down from top - .025"
Ring gap 1" up from bottom - .018"

Pistons measure (from top) 3.754"
Skirt measures (from the bottom) 3.778" ???
Is this correct? should the skirt be 3.754 if the top part of the piston is? Is this "out of round"?

I measured .008" clearance between P&C from the top when piston is all the way up, but there is very little clearance between the skirt and the bottom of the cylinder.

Can anyone shed some light on this?

Also, the Hastings part # is 4203

Muchos grassyass

Posted by: Racer Chris Sep 3 2003, 06:07 AM

The measurement at the piston skirt is where you compare with the cylinder bore. The top of the piston has much more clearance.
In order to get an accurate cylinder bore measurement you need a better bore gauge. It is very difficult to get a true reading with a "snap" gauge.

Posted by: swood Sep 3 2003, 01:04 PM

just a respectful bump...for more input

Posted by: porsche735 Sep 3 2003, 03:02 PM

Like I said, I just did this. When you measure your gaps you have to make sure that your rings are inserted square. With .018 you are probably fine, well within spec. I am concerned about your .007" variance (I think the ring is not square when measured). The piston will be sweeping from about 1/2" down to about 3 1/4" down.
What you are referring to is deck height. Figure out what compression ratio you want, cc your heads, and plug the results into the PP spreadsheet.

http://www.pelicanparts.com/914/technical_specs/914_compression_ratio.htm

But, like I said, don't use the bottom part....

To measure the deck height correctly you need to do teh following:
1) Use a few sockets and washers and bolt your cylinder to the case after installing the piston, rings and all.
2) Tap the "face" of the cylinder with a dead blow hammer
3) Tighten the nuts a little bit more. be careful as you don't want to bend the fins.
4) if you have a dial indicator use that to set TDC. Otherwise use the marks on the flywheel.
5) Measuer with a depth gauge at 12, 3, 6, and 9 o'clock positions to the top of teh cylinder from the piston.
6) take the average of the measurements. this is your deck height (if you are not using head gaskets which you shouldn't be.
7) To adjust, you must remove the cylinder, add or subtract shims, and reinstall the piston.
8) oh yea. And after each cylinder is done, have a beer..It will take you a while...

Chris

Posted by: J P Stein Sep 3 2003, 03:21 PM

The comparison between the upper and lower ring gaps is not as bad as it seems. What you are doing is comparing circumference of the bore in the 2 different places. The variation of the circumference is approx 3.14 times greater than the variation of the bore diameter.
You're actually looking at about .002 difference in bore dia.

Chris hit the nail on the head. Measuring bores is a job for a bore gauge. Your reading of 3.78 is short 2 decimal places. A dial bore gauge will read in tenths..
(.0001). An inside mic will do the trick for a quick and dirty job....if you have "the touch" you can read to half a thou (.0005) or so.

Posted by: swood Sep 3 2003, 04:21 PM

Thanks. I'll check it when I get home. I've got the heads cc'd and won't be using the gaskets. I was thinking of 8.5:1 CR.