• Registered: 2010-02-09
  • Posts: 8

Topic: replacing piston rings in 74 SB

I am new here and been working on my son's super beetle with help from him.  We had put a used head on (which I will never do again without having it checked) anyway ran ok for a bit had another used head had it rebuilt and put it on sounded great when we got it together but now after a 20 min drive is back to same thing.  Believe piston rings in 1 are shot need to know what is necessary before replacing those rings.  Bought them and the honing brush but if I don't need to hone would rather just put rings on.  Some advise please.
Jill

  • From: Canada
  • Registered: 2004-03-27
  • Posts: 630

Re: replacing piston rings in 74 SB

What are the symptoms that you're trying to fix, before we just jump into a "here's how you do what you're asking" type response and potentially have you chasing gremlins.

Hard to say whether or not the cylinders need honing, or if honing would do anything for them - depends on how worn they are and what all is wrong with the engine.

1979 Type 1 Convertible                                       1976 Scirocco (For Sale!)
1971 Type 1 Semi-Automatic Super                       1968 Type 1 Sedan
1961 Type 1 Sedan
1957 Type 1 Sunroof

Der Bugmeister's Website

  • From: somewhere over the rainbow USA
  • Registered: 2006-07-26
  • Posts: 1,882

Re: replacing piston rings in 74 SB

Welcome
As der bugmiester said it is more involved in that. but to replace the rings you need to check the cylinder walls for size, out of round etc. You need to clean up the piston and ring grooves, check ring gap in cylinder. I would hone them out, myself.  Did you check compression ratio when you installed other head?
But first symptoms would be nice to try and help you. Glad you are trying it yourself.

burrhead

A wise man makes his own decisions, an ignorant man follows public opinion.
  • Registered: 2010-02-09
  • Posts: 8

Re: replacing piston rings in 74 SB

Der Bugmeister wrote:

What are the symptoms that you're trying to fix, before we just jump into a "here's how you do what you're asking" type response and potentially have you chasing gremlins.

Hard to say whether or not the cylinders need honing, or if honing would do anything for them - depends on how worn they are and what all is wrong with the engine.

First low compression on 1 about 20psi, 2 had about 120psi, when you pull plug wires 1 and 2 off of dist cap there is no fluctuation in revs. whatsoever.  Boyfriend noticed oil cap bounced a little when we did compression check on 1 tells me possibly rings bad or gaps on rings lined up. Hope this helps, did not see burnt oil or anything visible on cylinder when we replaced the head but also didn't take the piston out.

  • From: Canada
  • Registered: 2004-03-27
  • Posts: 630

Re: replacing piston rings in 74 SB

Such a low reading in one cylinder compared to #2 would lead me to suspect something other than rings.  Did you check the compression in 3 and 4 also?  Did the problem occur soon after doing any maintenance on the car?

When you removed the old head, were all the head nuts properly torqued, or were any loose?  Likewise, when bolting up the new used head did you follow the torque sequences (two of them) up to the proper torque?

Where did you source the replacement head - was there any check made to ensure it didn't have issues either?

Possible problems leading to a low reading in the one cylinder include problems with the valve seat, the valve not closing completely, bad valve adjustment, cracked head, broken rings. 

Worn rings or cylinders would be more likely consistent in all cylinders, so checking them all is essential.

I'm not sure that misaligned rings would result in such a dramatic drop.

First thing to check is your valve adjustment.  I must be done when the engine is cold - let it sit overnight where you will do the adjustment.

Intake and exhaust should be adjusted to .006"

Here are a couple articles with step by step instructions, just in case:

http://www.vwtrendsweb.com/tech/0106vwt … index.html
http://www.glenn-ring.com/tech/valve_adjustment.htm

Some engine builders inadvertantly put the distributor drive shaft in backwards, which leads to an engine being "180" out.  What this means is that when you think you have the engine at TDC, it really isn't...so adjusting valves here can lead to some not closing at the right time.  To confirm to yourself that the cam is in the right position for the valves you're adjusting, put your fingers on the rockers of that cylinder and turn the engine a quarter turn in each direction.  If the rockers don't move, you're in the right position.

While checking the adjustment, also check the head nuts with your fingers to make sure none have loosened off.

Let us know what you discover!

1979 Type 1 Convertible                                       1976 Scirocco (For Sale!)
1971 Type 1 Semi-Automatic Super                       1968 Type 1 Sedan
1961 Type 1 Sedan
1957 Type 1 Sunroof

Der Bugmeister's Website

  • Registered: 2010-02-09
  • Posts: 8

Re: replacing piston rings in 74 SB

I did adjust the valves and the head was rebuilt by a VW mechanic that I trust.  When the old head was on there was a similar problem which leads me to believe the rings in that cylinder.  I also made sure all the nuts for the head were torqued in the proper order and to the proper specs. We did not check the other side for compression as it has been running the same every time they have been checked.  The valves were done after the head was in place and torqued.  When the compression test on #1 was done there was movement on the oil filler tube cover.  This was not true with #2.

  • From: somewhere over the rainbow USA
  • Registered: 2006-07-26
  • Posts: 1,882

Re: replacing piston rings in 74 SB

Best to do a leak down test to see where the air is going. if the rings are bad it would oil foul the plug or smoke. Drive it down the road with someone following to see if it smokes. The driver can't notice it sometimes

burrhead

A wise man makes his own decisions, an ignorant man follows public opinion.
  • Registered: 2010-02-09
  • Posts: 8

Re: replacing piston rings in 74 SB

burrhead wrote:

Best to do a leak down test to see where the air is going. if the rings are bad it would oil foul the plug or smoke. Drive it down the road with someone following to see if it smokes. The driver can't notice it sometimes

When the last head was on we did a leak down test and it took about a 10 to 15psi jump which is why I thought it was the rings on #1. Sorry I forgot to mention that.

  • From: B.C.Canada
  • Registered: 2005-01-26
  • Posts: 2,586

Re: replacing piston rings in 74 SB

jilli67013w wrote:
burrhead wrote:

Best to do a leak down test to see where the air is going. if the rings are bad it would oil foul the plug or smoke. Drive it down the road with someone following to see if it smokes. The driver can't notice it sometimes

When the last head was on we did a leak down test and it took about a 10 to 15psi jump which is why I thought it was the rings on #1. Sorry I forgot to mention that.

Miscommunication here. jilli67013w is referring to a wet compression test. Burrhead is suggesting something different. You pressurize the cylinders with air at TDC and time how long it takes to leak and you can hear where it's leaking from.

jim

'71 SB(DD only 79K(now 84K miles) & '78 FI Westy (project)
PO of '65 Beetle in '69, '70 Crewcab & '70 Ghia in '77
'71 Super inside rear vents now available
http://www.openroad.ca/volkswebbin/view … p?id=85915
  • From: somewhere over the rainbow USA
  • Registered: 2006-07-26
  • Posts: 1,882

Re: replacing piston rings in 74 SB

jamesdagg wrote:

. You pressurize the cylinders with air at TDC and time how long it takes to leak and you can hear where it's leaking from.jim

Yes you can hear where the air is coming out. thru oil cap = piston/rings, out exhaust = exhaust valve, out thru carb = intake valve
By chance did you measure the depth of the combustion chambers between the 2 heads?

burrhead

A wise man makes his own decisions, an ignorant man follows public opinion.
  • Registered: 2010-02-09
  • Posts: 8

Re: replacing piston rings in 74 SB

jamesdagg wrote:
jilli67013w wrote:
burrhead wrote:

Best to do a leak down test to see where the air is going. if the rings are bad it would oil foul the plug or smoke. Drive it down the road with someone following to see if it smokes. The driver can't notice it sometimes

When the last head was on we did a leak down test and it took about a 10 to 15psi jump which is why I thought it was the rings on #1. Sorry I forgot to mention that.

Miscommunication here. jilli67013w is referring to a wet compression test. Burrhead is suggesting something different. You pressurize the cylinders with air at TDC and time how long it takes to leak and you can hear where it's leaking from.

jim

Yes you are right miscommunication for sure guess I didn't understand thank you for the clarification.  Have never done that type of leak down and not really sure on how to do it if you can guide me I am sure I can do it.
thanks

  • Registered: 2010-02-09
  • Posts: 8

Re: replacing piston rings in 74 SB

burrhead wrote:
jamesdagg wrote:

. You pressurize the cylinders with air at TDC and time how long it takes to leak and you can hear where it's leaking from.jim

Yes you can hear where the air is coming out. thru oil cap = piston/rings, out exhaust = exhaust valve, out thru carb = intake valve
By chance did you measure the depth of the combustion chambers between the 2 heads?

Not exactly what you are talking about "the depth" of the combustion chamber? Please explain in a little more detail.  I have been working on VW's for about 6 years but only on a few mostly beetles and a few busses.

  • Registered: 2007-03-27
  • Posts: 2,422

Re: replacing piston rings in 74 SB

Often a Bad valve adjustment will hold a Valve open < compression will leak thru the open valve .
  You all know Me ?
I dont do compression Test on Bugg's except to Turn them over by hand while observeing the Rotor and at what Cyl. it is pointing too .
  Feel the compression by hand .
  Find a weak Cyl. < back the valves off .
See if it improve's the Compression on that Cyl.
Riddle Me this and Riddle Me that ?
How many threads above the nut are showing on the Valve adjuster's ?
  I highly suspect Bad Valve adjustment Possibly due too the Distributor Drive Being turned from it's Traditional T.D.C. #1 Posistion .
  Even if it has a Badd hole it should runn Ok with a Badd Miss ?
  Find T.D.C. #1 <, Then re-adjust the Valves .
  120 Buck's will buy a new Sett of Jugg's and Piston's .
Ive been re- ringin Piston's for 35+ year's there's considerably more to it than most People would think there is !
  First off you Dont Hone Cyl. too Clean them up of there Ring Groove, and wear .
  You Hone to Cross hatch so that the Ring's will seal .
  If the Cyl. is to worn << you need to Buy new Cylinder's and Piston's .
  How were the Head's Tested ?
  And answer the Adjuster nut Question .
                                                  Sean

  • From: B.C.Canada
  • Registered: 2005-01-26
  • Posts: 2,586

Re: replacing piston rings in 74 SB

You don't really need fancy equipment. You can buy an adapter to connect your compression tester hose to an air compressor type fitting.

http://www.type2.com/library/engineg/leaktst.htm

jim

'71 SB(DD only 79K(now 84K miles) & '78 FI Westy (project)
PO of '65 Beetle in '69, '70 Crewcab & '70 Ghia in '77
'71 Super inside rear vents now available
http://www.openroad.ca/volkswebbin/view … p?id=85915
  • Registered: 2010-02-09
  • Posts: 8

Re: replacing piston rings in 74 SB

Sean's wrote:

Often a Bad valve adjustment will hold a Valve open < compression will leak thru the open valve .
  You all know Me ?
I dont do compression Test on Bugg's except to Turn them over by hand while observeing the Rotor and at what Cyl. it is pointing too .
  Feel the compression by hand .
  Find a weak Cyl. < back the valves off .
See if it improve's the Compression on that Cyl.
Riddle Me this and Riddle Me that ?
How many threads above the nut are showing on the Valve adjuster's ?
  I highly suspect Bad Valve adjustment Possibly due too the Distributor Drive Being turned from it's Traditional T.D.C. #1 Posistion .
  Even if it has a Badd hole it should runn Ok with a Badd Miss ?
  Find T.D.C. #1 <, Then re-adjust the Valves .
  120 Buck's will buy a new Sett of Jugg's and Piston's .
Ive been re- ringin Piston's for 35+ year's there's considerably more to it than most People would think there is !
  First off you Dont Hone Cyl. too Clean them up of there Ring Groove, and wear .
  You Hone to Cross hatch so that the Ring's will seal .
  If the Cyl. is to worn << you need to Buy new Cylinder's and Piston's .
  How were the Head's Tested ?
  And answer the Adjuster nut Question .
                                                  Sean

OK I checked the valves once again all were at the right specs of .006, then put a new gasket on the intake manifold for 1 and 2, have compression but not the best did a check on all #1 was 115, #2 was 145, and #3 and #4 were 150.  Normally when I pulled the #1 and #2 spark plug wires it would not drop the rpms but this time it did just not much on #1, also checked and there are 2 threads on all adjuster nut's on intake and exhaust on #1 and 2.  Checked to make sure the rods were properly seated also and they were.  The head was rebuild by a VW mechanic in Tampa I am not sure exactly what he does as far as testing.  He replaced 2 or 3 valves as the stems were bent, reseated them and I can't remember what else.  I have the receipt just not readily available at the moment. Did not do a leak down test yet wanted to see what possible cures I had made so far.