#4 exhaust tightening, 1600 DP
Posted: Sat Jun 05, 2010 5:32 pm
2 years ago I started http://www.thesamba.com/vw/forum/viewto ... highlight= over at The Samba.
I finally had the right conditions to get the heads off
To summarize the Samba post:
‘71 bus w 23,000 miles on a brand new factory 1600 dp Mexican long-block. Completely stock except for SVDA and pertronix.
For the First 7,000 mi the # 1 and 4 exhaust valves were tighter than the others whenever I checked.
Since then the # 1 has stabilized, the other 6 valves have been relatively stable the whole time.
The # 4 exhaust valve is a concern, it continues to tighten up after every adjustment. Perhaps from .006 to .004 or less in 2000 miles.
Compression test:
1..................105
2..................114
3..................114
4..................109
All the spark-plugs looked good.
I really don't think it's getting hot [but am open to the possibility], I don't have gauges but no problems w the dipstick.
I've had this bus for over 25 years, have a pretty good feel for not pushing too hard, rarely drive over 57 mph.
At the time I'd read everything in the Samba forums, that looked relevant about stretched stems and dropped seats.
My problem doesn’t seem to be overheating related: I keep a pretty good eye on things; all tin is in place and well sealed, Hoover bit, etc; engine came w a blue crayon mark on the left side, back of the case, assume it’s for temp monitoring, it still looks the same; engine was running especially rich the first 14,000 mi.
Colin, you posted one of the last replies:
"I had a similar issue with my 38,000 mile Squareback engine, never torn down since the factory and I am losing clearance at #3 exhaust. I went all catastrophic in my suppositions, receded valve seat seemed very unlikely, and valve stem stretch seemed very unlikely with oem VW valves, but I took off the head at the third tight valve inspection.
The valve stem was correct diameter and the valve length was perfect.
The seat was perfectly positioned in the head.
But:
The contact area in the seat was this huge shiny cone. It had not been correctly (if at all) hardened at the factory. Got a new seat installed for $55.00 + overhaul gasket kit for $14.95 and threw it all back together.
Do not unnecessarily tear into the engine until you know what caused the closing clearance. If it is just a soft seat (not to be confused, please, with a receded seat which is softened aluminum in which the seat sits), fix it. Leave the rest alone. If you see heat event damage that actually stretched the valve, then let your investigations go deeper. You should have absolutely no issues with the rings and pistons and cylinders, and heads even, at only 23,000 miles. The original rings are good quality long wearing rings. Replacement rings are designed to aggressively seat. They will not last as long as what you have. Remember too, that the original engine assembly balance is better right now than it will ever be after you take it apart."
Now, heads off:
The 4E stem is out about .025" more than the others, and I can feel that the valve head is recessed about that much, so doesn't seem to be a stem stretching
Pushrods are good and straight.
Blue crayon mark also on outboard face of the # 4 cylinder.
Hard to say anything definitive about the coloring of the chambers as the recent runtime has all been short trips and idling, but they were very black, no sign of overheating.
No cracks.
I was a bit surprised to see that they are 043 101 375H heads, 33mm in. x 30mm ex., supposedly 9mm ex valve stems, tho I measure 8mm at the end I can see. I suppose the small valves mean less power, any other downside? I can live w less power if the small valves are not part of my problem.
2 of the studs came out when I was removing the head nuts, the upper ones near #3 and 4 ex valves. They seem solid when I replaced them. Should they be torqued in before the head is replaced? W a sealant?
The heads had small, 1.5 "x 1.75", tin baffles on the center underside of the fins, near the chamber side. These are in addition to the usual baffles under the barrels. First I've heard of them. They seemed to collect leaves etc, perhaps restricting airflow, I'm tempted to leave them off, as far as I know they are not part of the original design. Any thoughts?
Reckon I'll pack pack them off to Headflow Masters unless I hear of a better option.
If anyone has any comment on any of the above, I'm all ears, thanks.
I finally had the right conditions to get the heads off
To summarize the Samba post:
‘71 bus w 23,000 miles on a brand new factory 1600 dp Mexican long-block. Completely stock except for SVDA and pertronix.
For the First 7,000 mi the # 1 and 4 exhaust valves were tighter than the others whenever I checked.
Since then the # 1 has stabilized, the other 6 valves have been relatively stable the whole time.
The # 4 exhaust valve is a concern, it continues to tighten up after every adjustment. Perhaps from .006 to .004 or less in 2000 miles.
Compression test:
1..................105
2..................114
3..................114
4..................109
All the spark-plugs looked good.
I really don't think it's getting hot [but am open to the possibility], I don't have gauges but no problems w the dipstick.
I've had this bus for over 25 years, have a pretty good feel for not pushing too hard, rarely drive over 57 mph.
At the time I'd read everything in the Samba forums, that looked relevant about stretched stems and dropped seats.
My problem doesn’t seem to be overheating related: I keep a pretty good eye on things; all tin is in place and well sealed, Hoover bit, etc; engine came w a blue crayon mark on the left side, back of the case, assume it’s for temp monitoring, it still looks the same; engine was running especially rich the first 14,000 mi.
Colin, you posted one of the last replies:
"I had a similar issue with my 38,000 mile Squareback engine, never torn down since the factory and I am losing clearance at #3 exhaust. I went all catastrophic in my suppositions, receded valve seat seemed very unlikely, and valve stem stretch seemed very unlikely with oem VW valves, but I took off the head at the third tight valve inspection.
The valve stem was correct diameter and the valve length was perfect.
The seat was perfectly positioned in the head.
But:
The contact area in the seat was this huge shiny cone. It had not been correctly (if at all) hardened at the factory. Got a new seat installed for $55.00 + overhaul gasket kit for $14.95 and threw it all back together.
Do not unnecessarily tear into the engine until you know what caused the closing clearance. If it is just a soft seat (not to be confused, please, with a receded seat which is softened aluminum in which the seat sits), fix it. Leave the rest alone. If you see heat event damage that actually stretched the valve, then let your investigations go deeper. You should have absolutely no issues with the rings and pistons and cylinders, and heads even, at only 23,000 miles. The original rings are good quality long wearing rings. Replacement rings are designed to aggressively seat. They will not last as long as what you have. Remember too, that the original engine assembly balance is better right now than it will ever be after you take it apart."
Now, heads off:
The 4E stem is out about .025" more than the others, and I can feel that the valve head is recessed about that much, so doesn't seem to be a stem stretching
Pushrods are good and straight.
Blue crayon mark also on outboard face of the # 4 cylinder.
Hard to say anything definitive about the coloring of the chambers as the recent runtime has all been short trips and idling, but they were very black, no sign of overheating.
No cracks.
I was a bit surprised to see that they are 043 101 375H heads, 33mm in. x 30mm ex., supposedly 9mm ex valve stems, tho I measure 8mm at the end I can see. I suppose the small valves mean less power, any other downside? I can live w less power if the small valves are not part of my problem.
2 of the studs came out when I was removing the head nuts, the upper ones near #3 and 4 ex valves. They seem solid when I replaced them. Should they be torqued in before the head is replaced? W a sealant?
The heads had small, 1.5 "x 1.75", tin baffles on the center underside of the fins, near the chamber side. These are in addition to the usual baffles under the barrels. First I've heard of them. They seemed to collect leaves etc, perhaps restricting airflow, I'm tempted to leave them off, as far as I know they are not part of the original design. Any thoughts?
Reckon I'll pack pack them off to Headflow Masters unless I hear of a better option.
If anyone has any comment on any of the above, I'm all ears, thanks.