Exhaust valve/valves tightening. What's acceptable?

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wcfvw69
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Exhaust valve/valves tightening. What's acceptable?

Post by wcfvw69 » Fri Oct 14, 2016 10:32 am

SO, my engine that was built by a "pro" before I purchased the bus is showing some tightening exhaust valves, primarily 1 and 2. The engine has roughly 12k miles on it since it was last overhauled according to the rebuild paperwork by the builder. It's a basic stock engine but with 90.5 pistons (1776) and the rest of the engine is stock. The heads, cam, etc are stock spec. It's dressed and looks like a bone stock dual port 1600 with doghouse fan shroud.

What I've found the last three valve adjustments is a couple of the exhaust valves are slightly tight when checked. The builder used chromoly push rods, valve lash caps and stronger rocker arm shafts w/stock rockers. The intake valve adjustments are pretty consistent and rarely require adjustment.

What I'm finding is I have to back off the adjustment screw about 1-2 minutes each time I adjust the exhaust valves on 1 and 2. The valves are adjusted to loose zero meaning I tighten the adjuster while spinning the pushrod till it just starts to feel resistance to spinning it and then tighten the locking nut.

How much tightening of the exhaust valve is considered "normal"? I went about 1800 miles since the last adjustment.
1970 Westfalia bus. Stock 1776 dual port type 1 engine. Restored German Solex 34-3. Restored 205Q distributor, restored to factory appearance engine.

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Re: Exhaust valve/valves tightening. What's acceptable?

Post by Amskeptic » Fri Oct 14, 2016 4:55 pm

wcfvw69 wrote:SO, my engine that was built by a "pro" before I purchased the bus is showing some tightening exhaust valves, primarily 1 and 2. The engine has roughly 12k miles on it since it was last overhauled according to the rebuild paperwork by the builder. It's a basic stock engine but with 90.5 pistons (1776) and the rest of the engine is stock. The heads, cam, etc are stock spec. It's dressed and looks like a bone stock dual port 1600 with doghouse fan shroud.

What I've found the last three valve adjustments is a couple of the exhaust valves are slightly tight when checked. The builder used chromoly push rods, valve lash caps and stronger rocker arm shafts w/stock rockers. The intake valve adjustments are pretty consistent and rarely require adjustment.

What I'm finding is I have to back off the adjustment screw about 1-2 minutes each time I adjust the exhaust valves on 1 and 2. The valves are adjusted to loose zero meaning I tighten the adjuster while spinning the pushrod till it just starts to feel resistance to spinning it and then tighten the locking nut.

How much tightening of the exhaust valve is considered "normal"? I went about 1800 miles since the last adjustment.
One to two "minutes" or hours?

You have approximately one full turn back before your risk goes up exponentially for a valve seat problem. Assuming you get 75,000 miles before serious disassembly/machine work inspection is required, there will be 25 valve adjustments (assuming 3,000 mile intervals) in your future with these heads. That gives you a net of one half hour allowed per valve adjustment. But it is a exponential curve, so, anything more than an hour in one adjustment interval must be monitored. Due to all kinds of changing dimensions in a VW engine engine, I like to tell people that three subsequent changes in the same direction for any one valve is your warning.

The above has caveats!
a) re-done valve seats will be a more dangerous risk at 12 hours (1 turn) from relaxing the interference fit between the seat and the head aluminum.
b) any hot running episodes demand a next morning valve adjustment check if you have a valve or two on probation.
c) the rate of change is an important criterium for deciding to address a problem valve. If you lost an hour in 3,000 miles, that is a whole lot more relaxed than losing an hour in 1,000 miles or 500 miles.
Colin
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 91 414 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,113 miles

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Re: Exhaust valve/valves tightening. What's acceptable?

Post by wcfvw69 » Fri Oct 14, 2016 8:55 pm

Ah shit, I meant hours. Number 1 and 2 exhaust valves had to be backed off two hours this time. I never really paid that close of attention to my bugs valve adjustments because they don't get that many miles put on them. It seems like 1 or 2 exhaust valves on those engines tighten a slight amount as well.

I'll keep an eye on the exhaust valves on the bus. Next time I'll also see if all the valve stems are at the same height as well with a straight edge.

When you adjust the valves on your 70 after say 3k miles, what changes are typical on the adjustments. I'd be curious to hear what Robbie's finding on his valve adjustments as he crossed the country this year as well.
1970 Westfalia bus. Stock 1776 dual port type 1 engine. Restored German Solex 34-3. Restored 205Q distributor, restored to factory appearance engine.

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Re: Exhaust valve/valves tightening. What's acceptable?

Post by asiab3 » Sat Oct 15, 2016 12:19 am

wcfvw69 wrote:I'll keep an eye on the exhaust valves on the bus. Next time I'll also see if all the valve stems are at the same height as well with a straight edge.

When you adjust the valves on your 70 after say 3k miles, what changes are typical on the adjustments. I'd be curious to hear what Robbie's finding on his valve adjustments as he crossed the country this year as well.
The valve stem height test works on a new head, or a head with reworked valve seats, or a head with professional voodoo done. Since mine were bare bones new valves and 3-angle grind on scrap heap heads, when I installed the heads, the heights of a few stems were off by a thread at most. I did not know to check for it at the time… :pale:

Since you asked, I went about 9,000 miles without adjusting a single valve, checking every 3,000 plus the morning after some insane mountain pass where I put my ice chest on the gas pedal for almost two hours in second gear. At the 12,000 mile check, #1 exhaust valve was a half-hour tight, so I made good on it.

Are you sure you're not just hunting for a reason to put a model-year-correct single port engine in your 1970 bus? :geek:
Robbie
1969 bus, "Buddy."
100k miles with me.
279k miles on Earth.

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Re: Exhaust valve/valves tightening. What's acceptable?

Post by wcfvw69 » Sat Oct 15, 2016 7:19 am

wcfvw69 wrote:Ah shit, I meant hours. Number 1 and 2 exhaust valves had to be backed off two hours this time. I never really paid that close of attention to my bugs valve adjustments because they don't get that many miles put on them. It seems like 1 or 2 exhaust valves on those engines tighten a slight amount as well.

I'll keep an eye on the exhaust valves on the bus. Next time I'll also see if all the valve stems are at the same height as well with a straight edge.

When you adjust the valves on your 70 after say 3k miles, what changes are typical on the adjustments. I'd be curious to hear what Robbie's finding on his valve adjustments as he crossed the country this year as well.
Ok, I need to see your chart on hours vs. minutes again.. I was thinking about this an hour ago and drank too much last night. Bottom line, I'm having to back off the screw 1/8 to 1/4 turn. There, that was easier for my damaged brain..

Robbie, define 1/2 hour in turns? Sounds like you have some good valves and valve seats in place on your rebuilt head. And no, I'm perfectly comfortable with the 71 engine in my 70! She's runs beautifully! :drunken:
1970 Westfalia bus. Stock 1776 dual port type 1 engine. Restored German Solex 34-3. Restored 205Q distributor, restored to factory appearance engine.

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Re: Exhaust valve/valves tightening. What's acceptable?

Post by wcfvw69 » Sat Oct 15, 2016 7:28 am

Also Robbie,

who rebuilt your heads? Headflow masters? What seats and valves did he install?
1970 Westfalia bus. Stock 1776 dual port type 1 engine. Restored German Solex 34-3. Restored 205Q distributor, restored to factory appearance engine.

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Re: Exhaust valve/valves tightening. What's acceptable?

Post by sgkent » Sat Oct 15, 2016 11:30 am

Informational answer for anyone interested:

VW heads when new had a stem that was X above the spring deck. A really professional shop can tell you what X is. Usually that is not a published spec although it might be. When a head comes in to have a quality job done, the machinist measures the current height of each valve and writes the number down. If that number is very far off the normal height the machinist will probably stop and look things over to figure why it is different than what has been encountered before. He may even contact the owner to see if they know because there could be something special about the motor. Usually a difference results from a prior valve job. Then the machinist will do a valve job including guides, perhaps and seats - welding cracks in a VW head, or at least peening them closed if they are not in a worrisome place. Once the valve seats and valve heads are ground, the machinist will measure the valve again, and tip the valve a little to take off the height gained in the valve job and set it back to factory. Perhaps nothing will be done because it is common to reuse intake valves, and replace the exhaust valves. Once the height is acceptable then the springs are added and the spring height checked. If any spring has substantially changed it will be replaced. A shim may be placed under the valve spring to bring back a little lost tension. Then when the heads are complete the machinist may place it in a solvent tank and fill the ports with solvent - verifying that the valves completely seal and do not leak out. When I went to check the heads RIMCO did for us in Oct 2008 they did not have 3 angles on the seats. They went back. When I brought them home again they did not seal up with solvent so I took them back again. Eventually I had to hand lap them myself to get the solvent leaks to stop because RIMCO no longer had a skilled machinist good enough to do an A1 quality job. Everything else was fine. If the head is some other car - especially something that has overhead cams where lifter cups and shims are used to adjust the valves, then the machinist will put the stem height exactly back to where it was to minimize the work needed to adjust the valves.

If you see a valve clearance that is wearing wider It is usually the screw wearing but always check the valve stem for pitting. The valve should spin slowly when in use and that will leave a circle where the screw contacts the stem unless you have elephant / swivel feet. When the clearance gets tighter, it can mean that the cylinder is settling into the cylinder head, or the cylinder into the case. That should be a one time thing and stop after a couple valve adjustments. If however you see the clearance changing by say .001" tighter every time you check at every additional 3000 miles then you may have a stretching valve or a seat sinking. I keep a spread sheet of each valve's clearance at each oil change so I can see if there is any pattern developing. I am guessing you do the same Robbie - is that correct? Note: I only do this on my T4 bus because of the high temps the T4 head runs at. I did not do this on my 1971 doghouse cooler bus. Because I worked in a machine shop, I typically did those myself every 40,000 miles and replaced them at 80,000. Those heads would develop a small crack between valves that could be heli-arced or peened. They were so inexpensive back in the 1970's and early 80's that one just replaced them. VW intended that the heads cylinders and pistons would be replaced when an engine had a major overhaul.
Thank You -

Merlin The Wrench

Machine Work/Shop Recommendations: http://kentcomputer.com/77VW/machinework.pdf

Pointers on rebuilding an engine: http://kentcomputer.com/77VW/rebuilding_a_vw_engine.pdf

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Re: Exhaust valve/valves tightening. What's acceptable?

Post by Amskeptic » Sat Oct 15, 2016 6:28 pm

wcfvw69 wrote:
When you adjust the valves on your 70 after say 3k miles, what changes are typical on the adjustments. I'd be curious to hear what Robbie's finding on his valve adjustments as he crossed the country this year as well.
My Yuma flea market used heads have been a joy over the past 77,000 highway miles. The exhaust valves on the left side are a good full turn or two further out than the intakes. I lose about an hour every 3,000 miles on those exhausts, but I am pretty sure I don't care.
Colin

I pulled the original rebuilt heads out when the exhausts got to this point . . . only a couple of threads more than the intakes, but the rate of change was unacceptable:

Image
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 91 414 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,113 miles

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Re: Exhaust valve/valves tightening. What's acceptable?

Post by asiab3 » Sat Oct 15, 2016 9:22 pm

wcfvw69 wrote: Ok, I need to see your chart on hours vs. minutes again.. I was thinking about this an hour ago and drank too much last night. Bottom line, I'm having to back off the screw 1/8 to 1/4 turn. There, that was easier for my damaged brain..

Robbie, define 1/2 hour in turns? Sounds like you have some good valves and valve seats in place on your rebuilt head. And no, I'm perfectly comfortable with the 71 engine in my 70! She's runs beautifully! :drunken:

who rebuilt your heads? Headflow masters? What seats and valves did he install?
The chart is a clock! 1/12 of a turn of the screw = one hour. (See Colin's diagram below.) Your 1/8 to 1/4 turn is 1.5-3 hours.

My valves are Ivam stainless steel valves with original Volkswagen valve seats. Adrian did the three-angle grind and the chambers held gasoline overnight when I got them. We installed the valves together, since I wanted to make sure the keepers and valves worked together; there were reports a few years ago of these particular valves being ever so slightly too small for the keepers, to the point where the valve actually had some movement in the keeper once installed. (The valves were NOT cheap, so I had to make sure everything was kosher while I had a shop worth of parts at my disposal. Worth it.) The springs are new, stock stiffness. Porsche swivel feet adjusters keep the wear down to a minimum. When I removed the rockers, the valves and swivel feet still had indications of valve spin during normal operation, since the swivel feet are still offset the few thousandths like the old engine stock adjusting screws used to be.

Hope that wasn't too much information!
Robbie

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1969 bus, "Buddy."
100k miles with me.
279k miles on Earth.

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Re: Exhaust valve/valves tightening. What's acceptable?

Post by wcfvw69 » Sun Oct 16, 2016 8:05 am

Thanks Robbie for the excellent response. I couldn't remember seeing that diagram in the past if it was minutes or hours. So, with this reminder, I can say I had to back off the exhaust valves I mentioned earlier 1-2 hours. At the next valve adjustment, I'll also look at the adjustment threads closer for a comparison between them.

I'm not overly concerned at the moment. I just recalled Colin suggesting to keep a valve adjustment log when he was here 1.3 years ago. The shop that rebuilt this engine has a very good reputation. Since I reinstalled all the correct, original, rebuilt ancillary parts back on it (carb, distributor, etc) it runs beautifully. The builder installed a counter balanced crankshaft and it's very smooth and vibration free.

Thanks to everyone who replied to this question.
1970 Westfalia bus. Stock 1776 dual port type 1 engine. Restored German Solex 34-3. Restored 205Q distributor, restored to factory appearance engine.

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