Compression Issues
Ich fahre ein Kdf ein Tag - July 18th, 2006 at 12:22 PM
Hi AVD's, I am intending to purchase '58 Beetle but it is having compression problems. I know that cylinders can loose compression due to wear and
tear etc. But this car has had an engine rebuild in the last 4 years, the carbies have been fixed up, new fuel lines and tank. So what could it be?
could it just be valve issue? Your help appreciated.
H
PurpleT3 - July 18th, 2006 at 12:40 PM
Loose head studs. Check that all head studs are torqued to spec. Could also be worn valves. Four years is long enough to do 100,000km, if it's a
daily driver. Could still be worn rings. Test by pouring a small amount of oil into the cylinder and re running comp test. If comp goes up, rings
are worn
Bizarre - July 18th, 2006 at 12:43 PM
have a read through here
http://www.vw-resource.com/vw-resource.com_non_ssl/search.php?zoom_query=comp...
there are a heap of things go wrong with a motor resulting to low compression
First
What are the compression problems?? low - none??
What do you call a rebuild?? New pistons and barrels or a quick hone and new rings if you are lucky??
Could be
pulled head studs
dropped valve seats
valve badly adjusted and held open
distorted barrel
76camper - July 18th, 2006 at 08:33 PM
If its got low comp, you pretty much certainly going to have to rebuild, or at least a top end freshen up. Replace valves, seats and guides at least.
Possibly head studs as above, rings, barrels... list is long. Try the oil trick but generally crap compression WILL mean a rebuild.
Ich fahre ein Kdf ein Tag - July 20th, 2006 at 04:35 PM
| Quote: |
Originally
posted by 76camper
If its got low comp, you pretty much certainly going to have to rebuild, or at least a top end freshen up. Replace valves, seats and guides at least.
Possibly head studs as above, rings, barrels... list is long. Try the oil trick but generally crap compression WILL mean a rebuild.
|
Reading Muir's I figured as much. The car is supposedly not running hot, and sounds like normal no clunking (rings ok i guess) but i expect it would
be smokin' oil. Compression test figures showed that No.1. cylinder is stuck, and 70psi in the other cylinders so it sounds dead, head rebuild and
all things new there. The 4 year rebuild apparently was bottom end (according to owner), my guess she means crankshaft, and rods and pulleys etc but i
dunno. Cracked piston is also a possibility i guess.
76camper - July 20th, 2006 at 05:17 PM
Thats kinda good news, as hopefully you wont need to touch the bottom end (except inspect it). You will probably be able to get away with top end
freshen up (valves, seats and guides) and possibly hone cylinders and chuck in some fresh rings. If its not blowing smoke that would suggest the rings
are sealing well. One way to determine between compression loss due to rings or valves is as sed, take the comp reading of a pot, then put a fit of
oil through the spark plug hole and take another reading (after a few cranks). if the compression remains constant its a head issue.
VWCOOL - July 20th, 2006 at 06:24 PM
| Quote: |
Originally
posted by 76camper
If its got low comp, you pretty much certainly going to have to rebuild, or at least a top end freshen up. Replace valves, seats and guides at least.
Possibly head studs as above, rings, barrels... list is long. Try the oil trick but generally crap compression WILL mean a rebuild.
|
Um, valves, guides and seats won't do JACK if your rings are shot.
No comp could be as simple as a 'riding' valve due to tight tappets...or as bad as a scored bore that even new rings won't fix!
Ich fahre ein Kdf ein Tag - July 21st, 2006 at 10:39 PM
| Quote: |
Originally
posted by VWCOOL
| Quote: | Originally
posted by 76camper
If its got low comp, you pretty much certainly going to have to rebuild, or at least a top end freshen up. Replace valves, seats and guides at least.
Possibly head studs as above, rings, barrels... list is long. Try the oil trick but generally crap compression WILL mean a rebuild.
|
Um, valves, guides and seats won't do JACK if your rings are shot.
No comp could be as simple as a 'riding' valve due to tight tappets...or as bad as a scored bore that even new rings won't fix!
|
But a scored bore or distortion in the barrel should cause loud noises should it not? and the engine apparently runs sweet just no compression, must
find out if it is smoking...
Bizarre - July 21st, 2006 at 10:42 PM
umm.......... how can it run sweet if it has no compression :duh
Ich fahre ein Kdf ein Tag - July 24th, 2006 at 11:29 AM
he he yeah...thats what i thought, but i mean sweet in that it does not apparently sound any different, no loud, odd noises coming from the car's
engine! I dont get it either, Bizarre
H
VWCOOL - July 24th, 2006 at 11:42 AM
pop off a rocker cover and go looking for a stuck valve. No smoke means your rings may be okay. Maybe...
Ich fahre ein Kdf ein Tag - July 24th, 2006 at 05:10 PM
No smoke definitely, so probably a stuck valve on no. 1 cylinder. Guess the question is, when I get to look at it, will i go gung ho with a fully top
end rebuild or just fix what is broken.
tassupervee - July 24th, 2006 at 05:45 PM
| Quote: |
Originally
posted by Ich fahre ein Kdf ein Tag
........... the question is, when I get to look at it, will i go gung ho with a fully top end rebuild or just fix what is broken.
|
Mayyyyyteee, thats a question only you can answer....which may well be influenced by your wallet size...or lack of it.
Got no money? plop it up with S/H bits.
Got plenty spondulah? Build it up bigger and better with nice new bits.
You decide.
L8tr
E
Ich fahre ein Kdf ein Tag - July 25th, 2006 at 10:46 AM
tanks for tee help tassupervee, hmmm...i got a quote for a head rebuild as $300 is that reasonable?