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E1
Samba Member
Joined: January 21, 2013
Posts: 8748
Location: Westfalia, Earth
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 Posted: Sat Nov 08, 2025 11:03 am Post subject: Re: loss of compression on 2.1L, cylinder 2 (exhaust valve?) |
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| Nitramrebrab72 wrote: |
So as to put a bit of clarity to the hydraulic lifters, they have a piston/cylinder length of 4mm max, each turn of the adjusting screw is 0.8mm 2 turns 1.6mm. They should always be at least half full so that leaves 2mm divided by 2 for the half way point of the usable part of the cylinder equals 1mm divided by 0.8mm (1 turn) gives 1.25 turns is a recommended preload once broken in. VW recommended 2 then did a recall to 1.5 turns Bentley say a bit of both, Brickwerks now recommend 1 and a 1/4 which is the ideal position for reliability.
I am more happy with 1.75 turns not to put the rocker geometry out too much but you have to keep more of an eye and check on things. |
Been waiting with baited breath on whether these ^ numbers do apply, or if they need to be adjusted via Mark’s thread-pitch comment below…
This kind of info is valuable and goes into my permanent RAM.
| crazyvwvanman wrote: |
The 2.1 adjusting screws have a 1.0 mm thread pitch.
Mark |
_________________
If ever twice as rich, we’re gettin’ a double-wide
’84 “Westfailure”/2.1 Digijet/5.43 Ring & Pinion/Peloquin/D-rated BFG KO2s
AI has spoken to further illiteracy, to steal, to cheat, and to replace humans
The caveman’s first question to the headhunter: “Hey, you got any coffee?” |
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Nitramrebrab72
Samba Member
Joined: November 10, 2018
Posts: 989
Location: France
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| Posted: Sat Nov 08, 2025 11:52 am Post subject: Re: loss of compression on 2.1L, cylinder 2 (exhaust valve?) |
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| E1 wrote: |
| Nitramrebrab72 wrote: |
So as to put a bit of clarity to the hydraulic lifters, they have a piston/cylinder length of 4mm max, each turn of the adjusting screw is 0.8mm 2 turns 1.6mm. They should always be at least half full so that leaves 2mm divided by 2 for the half way point of the usable part of the cylinder equals 1mm divided by 0.8mm (1 turn) gives 1.25 turns is a recommended preload once broken in. VW recommended 2 then did a recall to 1.5 turns Bentley say a bit of both, Brickwerks now recommend 1 and a 1/4 which is the ideal position for reliability.
I am more happy with 1.75 turns not to put the rocker geometry out too much but you have to keep more of an eye and check on things. |
Been waiting with baited breath on whether these ^ numbers do apply, or if they need to be adjusted via Mark’s thread-pitch comment below…
This kind of info is valuable and goes into my permanent RAM.
| crazyvwvanman wrote: |
The 2.1 adjusting screws have a 1.0 mm thread pitch.
Mark |
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It depends on the ratio of the rocker arm of the engine and it's angle which varies depending how far the screw is out ,1 turn equals 1mm multiplied by 1.5 gives 1.5mm I rounded it to 1.6mm so as to have 0.4mm per quarter turn for simplicity but mind is buzzing to be bang on
....
I think 1.5 turns in is a good call and checking them every 50,000kms(30,000miles) and 7,500kms(5,000 miles) after a rebuild..
Brickwerks prefer 1.25 turns and will probably be better if valve seat wear recession is great than valve stem wear.
One thing for sure is 2 turns is too much... There is someone out there setting them with a gap of 0.006" no preload to take advantage of virtually never having to adjust them as long as the seats wear/sink faster than the stems wear if they don't
they will tap after a while.. Yes and with no preload they will prime with oil as the cam lobe is way higher than the depth of the hydraulic tappets cyl/piston...Don't confuse preloading with priming ... |
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crazyvwvanman
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Joined: January 28, 2008
Posts: 10476
Location: Orbiting San Diego
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| Posted: Sat Nov 08, 2025 1:06 pm Post subject: Re: loss of compression on 2.1L, cylinder 2 (exhaust valve?) |
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The lifter adjustment is done with valves closed.
Ideally, turning the screw in just compresses the lifter within its range.
Each turn of the screw equals 1.0 mm at the valve minus the ratio factor at the lifter.
The fairly small rocker ratio doesn't play that much of a role in the adjustment.
From another rocker thread.
| tencentlife wrote: |
......
OEM wbx rockers are 1.1:1 ratio, just like Type 1's.......
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Mark |
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E1
Samba Member
Joined: January 21, 2013
Posts: 8748
Location: Westfalia, Earth
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| Posted: Sat Nov 08, 2025 3:37 pm Post subject: Re: loss of compression on 2.1L, cylinder 2 (exhaust valve?) |
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Thanks Mark.
_________________
If ever twice as rich, we’re gettin’ a double-wide
’84 “Westfailure”/2.1 Digijet/5.43 Ring & Pinion/Peloquin/D-rated BFG KO2s
AI has spoken to further illiteracy, to steal, to cheat, and to replace humans
The caveman’s first question to the headhunter: “Hey, you got any coffee?” |
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Nitramrebrab72
Samba Member
Joined: November 10, 2018
Posts: 989
Location: France
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| Posted: Sun Nov 09, 2025 2:30 am Post subject: Re: loss of compression on 2.1L, cylinder 2 (exhaust valve?) |
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| westspeleo wrote: |
| Nitramrebrab72 wrote: |
it will take a short while of the engine running to clean the crust of carbon off the valve and seat something the glove test won't be able to do so won't be conclusive and could mislead to an unnecessary top end rebuild. |
I'm hoping that running for a bit might clean some crust off and help lead to an improvement in compression! I'm really hoping the exhaust valve itself wasn't damaged by being held open improperly. |
It should do as the slight play in the valve guides mean that it will ever so slightly rub together before fully seating...Failing that you could spray in some valve cleaner through the exhaust port...(Position the crank so the valve is just ever so slightly open) |
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westspeleo
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Joined: June 12, 2017
Posts: 33
Location: New River Valley, VA
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| Posted: Mon Nov 10, 2025 7:48 am Post subject: Re: loss of compression on 2.1L, cylinder 2 (exhaust valve?) |
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| Nitramrebrab72 wrote: |
| It should do as the slight play in the valve guides mean that it will ever so slightly rub together before fully seating...Failing that you could spray in some valve cleaner through the exhaust port...(Position the crank so the valve is just ever so slightly open) |
Another update:
I did about 40 miles of highway driving and then another 50 miles of back roads over the weekend. It initially was running rough, however, it again was not as bad as it was a month ago. At this point I picked up some fuel injector cleaner and topped the tank off with it and premium It took about a 1/4 tank to fill it back up. After this, the misfires went away pretty quickly. The remaining 50 miles were more or less misfire free. These miles were slower and hillier, for what it's worth. Once I got home I did another leakdown test on the hot engine. Leakage in #2 improved from 78% (measured cold) to 42%. I redid the test later cold and leakage increased to 61%, but that's still down quite a bit from what it had been.
An observation regarding the misfires. They occur when the engine is at high rpm and also when it is idling. The tach takes a dive whenever the engine misfires, e.g. it'll go from 3000-4000 rpm down to 1000 rpm, but quickly recovers. Is that typical? I don't think the motor is actually changing speed that quickly. This dipping tachometer symptom also happens when the engine speed is low, but I can't actually sense a misfire in how the engine is running at low rpms, the dipping tach is the only way I can tell. I should note that this not the tach wandering a bit as the idle stabilizer does its job (or doesn't, whatever the case may be).
While doing the leakdown tests I've noticed that the wires connecting to the distributor is kind of loose. When I snap the cap back on, I have to carefully hold the little wire mount thing against the lower part of the distributor housing, otherwise the cap won't hold it in place. If this is faulty, could it interfere with spark in somehow, causing or exacerbating misfires?
Regardless, I'm happy that the valve adjustment and perhaps fuel injector cleaner may be helping. Again, will do all the cylinders as soon as the new gaskets get here, and I will inspect the adjustment screws to see whether they have degraded any.
Again, thanks for all the help!
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1986 2WD Westy (4-speed) |
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Howesight
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Joined: July 02, 2008
Posts: 3422
Location: Vancouver, B.C.
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| Posted: Mon Nov 10, 2025 8:35 am Post subject: Re: loss of compression on 2.1L, cylinder 2 (exhaust valve?) |
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The tach needle bouncing down quickly is a very important symptom. There are only two things that can cause it:
1. The Hall sensor in the distributor (usually dodgy wiring at or near the connector);
2. Failing solder joint in the ECU.
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'86 Syncro Westy SVX |
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do.dah
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Joined: August 27, 2015
Posts: 861
Location: Washington
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| Posted: Mon Nov 10, 2025 11:25 am Post subject: Re: loss of compression on 2.1L, cylinder 2 (exhaust valve?) |
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| Yep, your clue is the compromised hall sender plug. It's only gonna get worse until ya fix that. |
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E1
Samba Member
Joined: January 21, 2013
Posts: 8748
Location: Westfalia, Earth
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| Posted: Mon Nov 10, 2025 11:40 am Post subject: Re: loss of compression on 2.1L, cylinder 2 (exhaust valve?) |
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Since putting fresh gas in helped, add a bottle of HEET in the red jug.
Any water in tank settles to the bottom where it’s drawn from. Adding even a quarter-tank can remix the fuel. Then the next day — and/or as gas quantity runs lower — the water’s back to the bottom and you’re right back where you were.
I think this possible issue is atop the “3-4000 rpm” glitch. The above advice for that is solid. I would add that whenever we have a coil issue it seems to happen at 4,000 rpm, no clue why.
_________________
If ever twice as rich, we’re gettin’ a double-wide
’84 “Westfailure”/2.1 Digijet/5.43 Ring & Pinion/Peloquin/D-rated BFG KO2s
AI has spoken to further illiteracy, to steal, to cheat, and to replace humans
The caveman’s first question to the headhunter: “Hey, you got any coffee?” |
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Nitramrebrab72
Samba Member
Joined: November 10, 2018
Posts: 989
Location: France
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| Posted: Mon Nov 10, 2025 2:52 pm Post subject: Re: loss of compression on 2.1L, cylinder 2 (exhaust valve?) |
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| westspeleo wrote: |
| Nitramrebrab72 wrote: |
| It should do as the slight play in the valve guides mean that it will ever so slightly rub together before fully seating...Failing that you could spray in some valve cleaner through the exhaust port...(Position the crank so the valve is just ever so slightly open) |
While doing the leakdown tests I've noticed that the wires connecting to the distributor is kind of loose.
Regardless, I'm happy that the valve adjustment and perhaps fuel injector cleaner may be helping.
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I think it was more likely to have been the intake valve or possibly both, you stated there was a hissing noise from the airbox on #2 compression cycle... Modern injector cleaner is with high polyetheramine levels are great for cleaning the intake valve, but will be burnt off in the combustion cycle for the exhaust valve, spraying some in 50/50 mixed with petrol through the exhaust port valve just slightly left open over night should do it..
The miss fireing is likely down to removing and re-fitting the plug leads serval times for the compression tests, you might of pulled a wire internally from it's plug by the sound of things... |
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