p/c and rings
Thursday, 12-Oct-00 00:24:42
i've heard some people say that re-ringing the piston during a rebuild is asking for trouble in the future, and the thing to do is to get a new
p/c set. what do you guys have to say? thanks in advance.
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Re: p/c and rings (Dave Nor-Cal Holleran) (12-Oct-00 00:41:26)
Re: dave's right (bugly) (12-Oct-00 01:36:34)
Re: p/c and rings (Gary Cooper) (12-Oct-00 09:14:06)
ah, blue printing. i think i'm going for a new set, blow-by was so bad after all. thanks guys. (n/t) (zen) (12-Oct-00 10:18:08)
Re: ah, blue printing. i think i'm going for a new set, blow-by was so bad after all. thanks guys. (Dave Nor-Cal Holleran) (12-Oct-00 11:41:01)
Where do you find the specs in the Bentley manual for 90.5s and 94s? I must have missed that page. (n/t) (Bruce Tweddle) (12-Oct-00 12:45:51)
Page 69 (n/t) (Gary Cooper) (12-Oct-00 14:56:43)
Re: p/c and rings (LONG) (John Connolly) (12-Oct-00 12:23:26)
Re:HOW MUCH MONEY YOU GOT??? IS IT DAILY TRANSPO??? (OR BEATER??) (n/t) (D.BERG) (12-Oct-00 13:44:03)
Uh oh, DOUG'S BACK! :-) (n/t) (John Connolly) (12-Oct-00 16:43:10)
not much, but i'm planning on doing it right this time! (more) (zen man) (12-Oct-00 21:41:20)
I believe that it is a balance. Most P/C's for rebuilds have many miles and lots of wear on them. Good for trash.....However, Have run used sets with low miles on them. If a quick
hone cleans them up and bore dia is in spec, then there is no problem with R/R them. Keeping in mind that they won't last as long as new ones. I am also of the opinion that line
boreing is OK too........ (Ohio ( mr. cheapskate) Tom) (12-Oct-00 23:50:23)
Re: p/c and rings
Thursday, 12-Oct-00 00:41:26
Yes indeed you're asking for trouble if you re- ring your engine. 20,000 miles is about all you'll get.
It's about 125.00 For a good set of pistons & Cylinders and all you have to do is drop them in. The Cima/ Mahle Sets have been pre
gapped and are ready to install once you clean off the cosmoline coating that they have on them to protect them from rusting & then paint
them with a High heat flat black paint.
Dave Nor-Cal Holleran
Re: p/c and rings
Thursday, 12-Oct-00 09:14:06
What is basicly being said here that new p/cs as I've measured come already at wear limit as per bently manual so they are not
rebuildable because if you hone them then they are beyond wear limit and will not last.To check and see if your set is rebuildable
measure piston skirt od and cly. ID and compare the difference to spec in bently manual. Also check ring end gap by taking ring off
piston and slide it squarely in cly and use feeler gauge to measure gap also compare this reading to spec in manual for wear limit.If
piston to cly clearance and ring gap are well within limits then hone and install new rings.Ring sets are about 20% of the cost of new PC
sets so your call.
Note I didnt give you the spec because you need to have a manual if your doing this type of engine work anyway.
Re: ah, blue printing. i think i'm going for a new set, blow-by was so bad after all. thanks guys.
Thursday, 12-Oct-00 11:41:01
Another idea if you have the money is to install a set of Total Seal Gapless Second Rings. I think they're around $150.00-$180.00 These
work great in my 65' and I'll never use anything less. I used the stock rings in the Cima/ Mahle sets but they never seated ( After 1500
miles of driving in my 65'.
If you keep the stock rings that come in the set, make sure that you stagger the ring gaps as you'd be suprised how many people do not
stagger the gaps. I stagger the oil control rings at 9:00 & 3:00 The 2 nd ring at 2:00 and the top ring at 10:00 again.
Most people think that this is too close but from what I've experienced, They will stay in this area and aren't likely to rotate to the bottom
of the cylinder as they can do with a larger gap.
Dave Nor-Cal Holleran
Re: p/c and rings (LONG)
Thursday, 12-Oct-00 12:23:26
Replace the set (unless it's a race engine and doesn't have many miles on it)
Horizontally opposed engines of any make ( VW, Porsche, Corvair, Lycoming, etc,)do not have cylinders that wear in a perfect circle,
they wear more on their downward-side (due to gravity), ending us as a measurable oval (bust out the mic sometime). Since the typical
cylinder hone, which was designed to be used on monobloc engines, follows the BORE of the cylinder, honing does nothing but smooth
the walls on your oval-shaped bore. (don't believe me? Measure it after a hone)
To achieve a properly centered, truly round cylinder you must re-bore. But before doing so you must install the jug into a special fixture.
Back when Volkswagen overhauled their engines at the factory they spent millions trying to get the same service from overhauled jugs...
gave up when they figured out that it was less expensive to simply melt down & recast the old jugs rather than try to remachine them. (A
factory overhauled engine had the same warranty as a new one. But the ones with used cylinders had a habit of crapping out early forcing
VW to honor the warranty... and they
spent millions trying to figure out why the reconditioned jugs failed.)
The fact that the cylinder walls kept getting thinner had a lot to do with this too -- 85.5's
are just bored-out 83's, 92s are bored out 90.5s, etc. The thinner the wall, the more difficult to maintain alignment during the re-bore.
You'll hear all sorts of stories by "mechanics" to the contrary -- how someone threw in a set of rings and ran another zillion miles. Such
stories are usually bullshit. Hone the jugs, throw in a set of rings, it'll run nice... for a while. Easy way to make a quick buck, if the
customer is some kid; kids seldom keep their bugs or buses more than a year or two, since they sell them with another wheezing (and
leaking) engine to another 18 year old kid who immediately discovers the VW mags, and finds great companies like GEX, Mofoco,
Bergmann, to supply an engine with a fantastic warrantee (too good to be true?). The cycle then repeats, unless they take their lumps and
rebuild it RIGHT with good parts. I went thru this cycle, and didn't go to the Dark Side (watercooled. :-) )I'm sure many of you went thru
the same thing on the learning curve. You have to learn the hard way.
As to your pistons, the wear-surfaces are the ring-lands. Thats where the top & bottom of the piston rings form their seal. Putting in a
new set of rings doesn't make any sense unless you overhaul the pistons. That means having the
grooves re-machined to be perfectly perpendicular to the axis of the piston. The tricky bit here is that the inner corner of the groove must
have a subtle radius. Cut a square corner, as you see all the 'experts' doing when they use an old piston ring as a carbon scraper, and you
create a stress-riser -- the piston will crack right there in the corner. Back in the day, all
automotive machine shops overhauled pistons, but now the cost of labor is so high and the price of replacement pistons so low, the only
slugs that can justify being overhauled are high-buck forged racing items (JE, Wiseco, etc).
All of that should give you some idea why the smart money is on a new set of P&C's rather than overhauling the old ones.
Just replace em', they are cheap.
I believe that it is a balance. Most P/C's for rebuilds have many miles and lots of wear on them. Good for trash.....However, Have run
used sets with low miles on them. If a quick hone cleans them up and bore dia is in spec, then there is no problem with R/R them.
Keeping in mind that they won't last as long as new ones. I am also of the opinion that line boreing is OK too........
Thursday, 12-Oct-00 23:50:23
I don't have lots of money to spend on my ride so I tend to go for the most bang for the buck. Even if it doesn't last. I don't mind R/R
every 10 or 20K mi. I pull the heads off to freshen them up anyway. Some may call me cheap. Some may say that i'm the "Poor man who
always pays more". Maybe so....I can't help it.... I love to work on my car and I godda' go faster...Hmmmm, A new case, or a stroker
crank? See my point. I don't rely on my car as a daily driver, I have 2 engines and all winter to get ready....
Ohio ( mr. cheapskate) Tom