TheSamba.com :: View topic

Wed Jul 23, 2008 6:13 pm

As some of you may be aware, I recently bought a '71 super vert for my wife. The first job was a brake rebuild, which went great. I also did all the usual 'Do it so I know when it was done stuff' - oil/cap/rotor/plugs/timing/valve adjustment. I did a compression test and got not great, not awful numbers: 110, 135, 115, 135 respectively on the 1-2-3-4 cylinders.

When I bought it, I drove it home about 4 hours at highway speeds without incident -- just typical poor tuning and crackling on long inclines. After my work, it seemed to run fine. Then my wife drove it to work and about 1/2 hour of highway time, it broke down on her. I managed to limp it home; it behaved a lot like a flooding carb. It would only start with the throttle wide open, there was popping in the enigne noise, etc. It also seemed to be running very hot; I mistakenly used the wrong heat range plugs (W7AC).

After a carb rebuild and much swapping of known-good parts from my Ghia and no progress, it finally occured to me to recheck compression. 1 & 2 were unchanged, but I got 45 and 45 on 3 & 4. It started raining before I could pop the valve cover for further inspection.

So, whaddaya think could cause this sudden drop on one side? Pulled studs? Cracked head? Bad valves? I'm hoping it's something stupid I can solve without dropping the engine, but I know that's a long shot.

Thanks in advance

Wed Jul 23, 2008 7:19 pm

Look under the engine where the heads meet the case for evidence of a head leak. Sounds like you have valve or head problems for sure. The cause is unclear without more history I guess. Sounds like it overheated.

Wed Jul 23, 2008 7:26 pm

"...crackling on long inclines"????

Wed Jul 23, 2008 7:51 pm

Front back side to side
head leak pop on inclines
front back side to side
head leak pop on inclines

shake it, shake that head stud dandy
head stud, oh so loosey
head seal you're lookin leaky
now pop that head leak!

Check it out dood.

Wed Jul 23, 2008 8:06 pm

mharney wrote: Front back side to side
head leak pop on inclines
front back side to side
head leak pop on inclines

shake it, shake that head stud dandy
head stud, oh so loosey
head seal you're lookin leaky
now pop that head leak!

Check it out dood.

:) :) :)

Wed Jul 23, 2008 8:16 pm

Das Dragon wrote: "...crackling on long inclines"????
The crackling sound that I assume is detonation associated with poorly set timing or bad gas.

Thu Jul 24, 2008 8:02 am

That's probably why the valves and/or seats are toasted. Preignition is death.

Thu Jul 24, 2008 9:08 am

Das Dragon wrote: Preignition is death.
Yeah. Could be that when I heard it driving it home, I knew well enough what it was to back off the throttle, but when/if she heard it, she kept pressing it. Or it just coulda been that the engine had been kept in poor enough tune for long enough that it was just a matter of time before it went kaput. Either way, that's why I love VWs... "Oh, I need to rebuild the engine? That's a nice saturday afternoon."

So, it looks like I'm dropping the engine. Oh well. As long as I have it out, I'll do a C/P job to correct those weak compression numbers on 1 & 3 and shore up all the oil seals.

Next question... assuming my valves are burnt up (which is a pretty good bet), is it advisable to get new valves/ guides/ springs/ seats/ etc and rebuild my current heads, or just get new complete heads? How can I tell if my heads are shot and not rebuildable?

Thu Jul 24, 2008 9:15 am

Its probably best to get new heads especially with how cheap they are

Thu Jul 24, 2008 10:25 am

Bill271 wrote: Its probably best to get new heads especially with how cheap they are
ditto.

Sun Jul 27, 2008 9:45 pm

Update:

I dropped and tore down the engine this weekend. Turns out it didn't need much. Just new cylinders, pistons, and heads. :)

Found that the cylinders were 92mm, and ALL the cylinder walls and pistons were heavily damaged. I'm replacing them with the thicker 90.5mm. The heads were rebuildable, but needed machining as well, so I bought a pair of 042s with S/S valves instead for not much more than the rebuilds woulda cost.

I'll post some pics shortly.

Sun Jul 27, 2008 11:20 pm

If you don't mind telling, where'd you pick up the new heads?

Mon Jul 28, 2008 4:16 am

IntrstlarOvrdrve wrote: If you don't mind telling, where'd you pick up the new heads?
Don't mind telling at all... I took a ride out to Bug City. He's about an hour drive for me. The heads were $250/ea.