#4 exhaust tightening, 1600 DP

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denjohn
Getting Hooked!
Location: Tracy, MN
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#4 exhaust tightening, 1600 DP

Post by denjohn » 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.
Peace
'71 bus, stock running gear ex SVDA and pertronix

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Amskeptic
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Re: #4 exhaust tightening, 1600 DP

Post by Amskeptic » Sun Jun 06, 2010 10:38 pm

denjohn wrote: 23,000 miles on a brand new factory 1600 dp Mexican long-block.
don't think it's getting hot

Now, heads off:
The 4E stem is out about .025" more than the others,

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.
What does ".025" out" mean? That the stem sticks up .025" higher than the tips of the other valves? That is 12 valve adjustments of losing .002" clearance every time. Check the seat/valve contact width. Anything more than 2.2mm is wear.

Those tin baffles are critical and your comment about leaving them off is a demerit against the IAC credo and humanity. :blackeye:
They are the 1600 answer to the Type 4 baffle in the same place, the Type 4 just has them as part of the entire under cylinder deflectors. Their purpose is to block airflow at the intake valve ports so the heads will heat and cool more evenly. Take them off and enjoy your cylinder head cracks.

Your valve stem/adjustment nut sizes are classic Mexican fuel injection valve sizes, if you have the chance to resize the valves to carbureted specification (but no more), you will need new rocker arms and valve guides, but I don't think you will notice a constriction in breathing with these valves until about 4,500 rpm +.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

denjohn
Getting Hooked!
Location: Tracy, MN
Status: Offline

Post by denjohn » Mon Jun 07, 2010 10:07 am

Thanks Colin,
Right.....the stem sticks up .025" higher than the tips of the other valves.
When I look at my adjustment log, that's about the cumulative total I figure I'd lost in 23,000 mi.

"Check the seat/valve contact width. Anything more than 2.2mm is wear."
Something is obviously wrong w that valve/seat and my living and workspace situation make an engine pull quite a hassle, so want to put the next one off as long as possible.
I haven't found a rebuilder that I'm comfortable with within driving range. So, my thought is to just pack both of them off for a complete recondition.
Does that make sense?

Tin stays on, thanks for the explanation.
How many demerits are we allowed?

Good to hear you say that the valve size is not an issue, should work fine for my needs.
Thanks for the heads up re rocker arms and guides if I ever think about bigger valves.
Anyone know what 4th gear 4500 RPM translates to in MPH on a '71 bus?
Peace
'71 bus, stock running gear ex SVDA and pertronix

denjohn
Getting Hooked!
Location: Tracy, MN
Status: Offline

Post by denjohn » Thu Jul 15, 2010 8:35 pm

I got the heads back, reconditioned and a new seat........seems the problem was a soft seat, as Colin mentioned in the original Samba thread.

I'm wondering how long one could run w a soft seat that is recessing at a rate of .001" per 1000 mi.
That would only be 1/16th of an inch after 62,500 mi.
If one is confident that it is not overheating related damage, this 'soft seat' seems a likely culprit.
Peace
'71 bus, stock running gear ex SVDA and pertronix

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Amskeptic
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Post by Amskeptic » Thu Jul 15, 2010 9:40 pm

denjohn wrote:I got the heads back, reconditioned and a new seat........seems the problem was a soft seat, as Colin mentioned in the original Samba thread.

I'm wondering how long one could run w a soft seat that is recessing at a rate of .001" per 1000 mi.
That would only be 1/16th of an inch after 62,500 mi.
If one is confident that it is not overheating related damage, this 'soft seat' seems a likely culprit.
1/16" is the difference between living with a scratch on your neck and bleeding out from a breached carotid artery, too . . . .

Once the contact surface is huge, like in the Squareback, it is only a matter of time before a little piece of carbon gets stuck on that huge surface and burns the valve. The unit pressure at the correct width prevents carbon induced pitting.
ColinWeLikeHardSeats
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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