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low compression on back cylinder
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BOATPOKER
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PostPosted: Sun Jan 30, 2011 2:03 pm    Post subject: low compression on back cylinder Reply with quote

removed the heads and cylinders, should the last rings be tight or loose

tight
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loose
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chucked
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PostPosted: Sun Jan 30, 2011 2:24 pm    Post subject: Reply with quote

All the rings should be loose. Thats probably your problem
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JerryMCarter1
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PostPosted: Sun Jan 30, 2011 5:49 pm    Post subject: Reply with quote

Rust on the rods. ??
Man you better take it all the way down for s serious look ! And check everything
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BOATPOKER
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PostPosted: Sun Jan 30, 2011 7:14 pm    Post subject: Reply with quote

What size rings do I need if the cylinder bore is 90mm?
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PostPosted: Sun Jan 30, 2011 7:59 pm    Post subject: Reply with quote

run another thread with that exact question
so that it hits the face baord of Samba

the rings look to small
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johnnypan
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PostPosted: Sun Jan 30, 2011 8:00 pm    Post subject: Reply with quote

90.5mm rings....that engine sat for a long time at one time or another,the oil control ring has rusted and siezed in the ring groove.imagine there are a whole lot more rust issues inside that case.
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BOATPOKER
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PostPosted: Sun Jan 30, 2011 8:20 pm    Post subject: Reply with quote

The PO let it sit for 7 years, when I got it the motor was seized, but I got it to run then it puke oil due to rotted push rod tubes, that and since number 1 cyl had only 70 lbs compression I pulled the motor.
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JerryMCarter1
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PostPosted: Sun Jan 30, 2011 9:06 pm    Post subject: Reply with quote

I would do a complete tear down and take the time to clean and replace as necessary
Of - look for an inexpensive used motor somewhere. One that you can hear it run or some reliable history of its condition.

Although I have had sitting engines come back on their own. Maybe you could just start to drive the piss out of it and hope for the best -- often rings start working and the rest - use 5- 30 oil --- so that the five gets into everything
But usually something serious goes wrong just down the road a few hundred miles
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johnnypan
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PostPosted: Sun Jan 30, 2011 9:21 pm    Post subject: Reply with quote

Marvel mystery oil,run a pint in with the oil run it for a few miles,drain and repeat.But odds are it has to come down.
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JerryMCarter1
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PostPosted: Sun Jan 30, 2011 10:10 pm    Post subject: Reply with quote

I had forgotten about that stuff
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BOATPOKER
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PostPosted: Mon Jan 31, 2011 6:08 am    Post subject: Reply with quote

Thanks, My plan is to hone the cylinders and replace the rings, run it with MMO and keep my fingers crossed.

Now that the motor is apart and the bore 90mm and the stroke is 72mm
Can I establish what soze this motor is?
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JerryMCarter1
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PostPosted: Mon Jan 31, 2011 8:50 am    Post subject: Reply with quote

the math is Pie(3.14) times R(radius) squared = ( area ) of the cylinder,,,, times the stroke ( distance ) of piston travel ,,,,times four ( cylinders )
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candymustang65
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PostPosted: Mon Jan 31, 2011 8:57 am    Post subject: Reply with quote

I beleive if your talkin 90.5 by 72 mm it would be a 2019cc .
It's definately stroked I can tell by the shorter B piston's .
Or least has appearance of stroked with those piston's .
Usually it's the ring width or thickness that matters as long as you get the right diameter 90.5 or on the piston top it will say 90.48 .
Im not a big fann of Marvel or used engines < It's B.S. !
Tear it down to a short block check every thing as in do not assume this engine was assembled correctly .
Compression testing is ???
Bleepin knuckle head's dont know there a--- from a hole in the ground alway's with the leak down and compression testing .
Very rarely do I actually perform compression testing on a V.W.
The result's of compression testing are only as good as the person who perform's them .
Reason's are many and complex and the result's are usually redundant .
Often if you back the valve adjuster off on a low cylinder the cylinder compression will come up .
Look at the heads see what kind of head's they installed on this motor ?
Then get a reccomended CCR for what your runnin .
Mean's you will need to CC the heads < measure combustion chamber with liquid .
Then a deck height measurement .
Usuall here is no more than 9-1 CCR ( Cylinder compression ratio ) for the street on pump gas .
You can test the head integrity by pouring gas intoo the exhaust ports and intake's while observeing that cylinders valve .
If gas leak's thru immediately indicates burned or badd valve if it seep's thru slowly after 30 second's or so indicates valves are sealing .
We have a CCR calculator here on the samba .
You can type in your head CC measurement , Bore and stroke , and deck height , then the calc will tell you displacement and CCR .
Sean
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BOATPOKER
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PostPosted: Mon Jan 31, 2011 9:14 am    Post subject: Reply with quote

Sean,

The cylinder bore measures 90 mm are 90.5 rings too large?
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JerryMCarter1
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PostPosted: Mon Jan 31, 2011 12:42 pm    Post subject: Reply with quote

not sure
sounds right
check a supplier
rungs have to push out to gather air and oil
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ashman40
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PostPosted: Tue Feb 01, 2011 9:38 am    Post subject: Reply with quote

BOATPOKER wrote:
Sean,

The cylinder bore measures 90 mm are 90.5 rings too large?

I think the face of the piston will have the true diameter stamped into it. If you clean off the piston you may be able to see it.
(sorry about the pic size)
Image may have been reduced in size. Click image to view fullscreen.

This one looks to be 85.46mm (I think that's a "6"?) from a stock 1600cc. See stamping at 4-o'clock position.
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'75 Beetle 1200LS (RHD)
"stock" 1600 w/ 34 PICT-3 carb & S/A tranny
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BOATPOKER
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PostPosted: Tue Feb 01, 2011 6:38 pm    Post subject: Reply with quote

no markings from the research they are NPR 90 mm stroke 82 pistons, still cannot find rings for these
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candymustang65
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PostPosted: Wed Feb 02, 2011 9:53 am    Post subject: Reply with quote

Ashman is correct should be stamped on the top of the piston as to the piston diameter .
Ashman is holding a 85.45 stamped piston wich is 85.5 rounded out .
As to type B piston's these are shorter piston's than the Type A and many different version's or brand's exist .
Carb spray and your thumb rubb should present some numbers in my experience .
But realize the old school guy's did a lott of stuff that is beyond my expertise these could be Mogul piston's or even TRW or ?
NPR does ring a bell with me .
Just not registering with me this mornin and I cant go look cause I moved into a Itchin house and movin my garage to new digg's .
NPR ? ehh maybe this evening I can look thru some old B piston's at the other place see if I can find somethin with NPR on it .
If not your left with mikeing them .
I should know or probably do know just cant pull it out this mornin Im old and tired under stress of a move ?
Or take um to some one reputable to buy your ring's .
NOTE : 3 different ring width's out there in my experience so make sure the width / thickness of the ring is correct as well as the diameter and there application .
Sean
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BOATPOKER
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PostPosted: Wed Feb 02, 2011 10:23 am    Post subject: Reply with quote

Image may have been reduced in size. Click image to view fullscreen.

They are 90mm I believe the rings need are 1.5,1.5,4.0 oil, should I measure the piston or the ring itself?
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JerryMCarter1
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PostPosted: Wed Feb 02, 2011 10:27 am    Post subject: Reply with quote

check it against another mic
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