Home Technical Discussions Volkswagen Vanagon: 1980-1991 (T3)

Volkswagen Vanagon: 1980-1991 (T3) failed '87 vanagon head replacement


Permlink Replies: 3 - Pages: 1
Last Post: Aug 23, 2013 7:55 AM Last Post By: RickW
timinnm2

Posts: 2
Registered: 08/20/13
failed '87 vanagon head replacement
Posted: Aug 20, 2013 4:13 PM
  Click to reply to this thread Reply
Have just completed installing used cylinder heads on my í87 Vanagon and need some help on a couple of issues. A broken alternator, water pump belt caused serious overheating, enough to melt the thermostat housing and create cracks between the valve seats. I installed two used heads from an í84 van that had spun a main bearing. Ergo, I knew their history and felt they were in good enough condition to get me running again.
However on start up the engine does not idle when cold and then once warm enough to idle it will surge from 1000 rpm to 4000 and there is also an intermittent popping/small backfire from the 3/4 head.
I have checked and rechecked the seating of the pushrods and rocker arm adjustment to no avail with regard to the backfire. As for the idle speed surge I have no clue what could be the cause. Did the excessive heat destroy a sensor and if so, which would cause this type of problem? Temp Sensor II ?
Iíll be ever so grateful if anyone has some insight into what the solution might be.

Edited by: timinnm2 on Aug 20, 2013 4:39 PM
RickW

Posts: 718
Registered: 02/16/05
Re: failed '87 vanagon head replacement
Posted: Aug 21, 2013 7:47 AM   in response to: timinnm2 in response to: timinnm2
  Click to reply to this thread Reply
Hello, timinnm2

I'm going to start by making a couple of assumptions:

-your block and cylinders were unaffected by the overheat
-you torqued the new heads down properly and they're sealing properly

You said you JUST completed the job. How recently was it? I just completed the same job (back in late June) on a 1991 Vanagon. At first, it didn't want to start and run properly - similar symptoms - wouldn't idle properly on startup, ran erratically, etc.

In the end, once I had run the engine a while and driven it a few miles, it started behaving normally. Not a scientific diagnosis, but that's what happened.

Another thing you might want to look for is a vacuum leak. Your problem might be due to the temp sensor (did you re-use the one from the melted thermostat housing?), or an out-of-adjustment throttle position switch.

Regards,
Rick W
Bentley Publishers
timinnm2

Posts: 2
Registered: 08/20/13
Re: failed '87 vanagon head replacement
Posted: Aug 23, 2013 12:27 AM   in response to: RickW in response to: RickW
  Click to reply to this thread Reply
Hi Rick,
Thanks for responding and my apologies for not getting back to you sooner. Unfortunately the first assumption you made is still in question as I knew of no way check compression until I got the heads back on. But now that itís back together, and yes, they were properly torqued, the readings are dismally low, 85 to 90 on all four cylinders but oil pressure is still good around 40 lbs.

I tested the temp sensor and throttle switch and both are good. Also checked for vacuum leaks with carb cleaner and found none. Unplugged O2 sensor as well, still no change. It will idle without surging if the air meter is unplugged but is extremely rough.

What has me really puzzled though is the reading on the leak down test. The orifice on my homemade tester is 1/32Ē and all 100 PSI are lost in the cylinders. I can hear the leak from all valves in all cylinders and the confusing part is, if I tighten the adjuster slightly it, the air sound, goes away but then comes back in a few seconds. Iím guessing that with each tweak Iím actually opening the valve a bit to a point where the air is passing too freely to be heard and then it is slowly settling back into a leaky seat as the lifter is losing oil. Does that sound correct? Guess the heads werenít as good as I thought they were.

Also wondering about the old burnt oil that must still be trapped in the lifters and if that might prevent them from functioning properly. Another observation, when the rocker adjustment screws are finger tight against the pushrods. some, not all of the pushrods can be depressed into the lifters as if they are not holding oil properly. Could a number of fouled up lifters be causing all the running problems?

I would normally have pulled the engine and been more methodical with my approach. but this happened away from home and Iím working in a dirt driveway during monsoon season and as much as I had hoped for a quick fix that is obviously NOT going to happen. Your thoughts and or comments will be appreciated.

Best Regards,

Tim C
RickW

Posts: 718
Registered: 02/16/05
Re: failed '87 vanagon head replacement
Posted: Aug 23, 2013 7:55 AM   in response to: timinnm2 in response to: timinnm2
  Click to reply to this thread Reply
Hello, Tim

I'm not sure how much more advice I can offer at this point. Your approach with the compression and leakdown tests is exactly what I would have recommended next.

"Iím guessing that with each tweak Iím actually opening the valve a bit to a point where the air is passing too freely to be heard and then it is slowly settling back into a leaky seat as the lifter is losing oil. Does that sound correct? Guess the heads werenít as good as I thought they were"

While I would absolutely need to at least partially suspect a homemade leakdown tester, you also supplied compression readings, which lends at least some validity to the leakdown test. But, I don't personally have much practical experience with the process, so I can't be of much help toubleshooting the leakdown test itself.

"Also wondering about the old burnt oil that must still be trapped in the lifters and if that might prevent them from functioning properly. Another observation, when the rocker adjustment screws are finger tight against the pushrods. some, not all of the pushrods can be depressed into the lifters as if they are not holding oil properly. Could a number of fouled up lifters be causing all the running problems?"

I suppose the lifters might be a factor. If the valve adjustment is more or less OK, then simply running the engine a while may help a bit with the lifters. You mentioned the oil pressure. Is that with the engine hot or cold? I've seen oil pressure vary greatly based on temperature. On a previous Vanagon engine, I had oil pressure that seemed high enough with a cold engine and dropped to near zero when the engine was hot.

Regards,
Rick W
Bentley Publishers

Point your RSS reader here for a feed of the latest messages in all forums

Popular Discussions:
No popular dicussions.