Low Compression after Rebuild and 400 Miles

[biondic123]

My guess is the answer to my problem is simple and that I'm not going to like the answer.

I recently rebuilt a 2.1L motor for my 1988 Vanagon using a 2.2L rebuild kit from a well known supplier. I've been putting a few miles on it every few days or so to break it in. Yesterday, I topped off the oil (I think it was overfilled) and took it down the highway for 40 miles traveling anywhere from 55 to 70 miles per hour. When I came off the highway, the motor stalled and wouldn't start. I was then towed home. I checked compression and the cylinders are all low (40 to 70 psi). I also noticed some oil in the throttle body. I have an oil gauge and it was running about 20 to 22 psi on the highway, and my oil light and buzzer were going off even though the gauge was above 20psi.

Did I blow up the motor? If so, any ideas why? I will be happy to answer questions. Would too much oil cause the lack of compression?

[garryv84]

Did you check all the clearances when you rebuilt it?

At 4000rpm you should have 40psi oil pressure. Are you should your gauge is correct? Check against a manual gauge.

Low oil pressure and low compression pressure are two different things.

[biondic123]

This is a bit embarrassing. I did not check all clearances. To save money, I did not replace any of the crankshaft bearings. I suspect this is why the oil pressure is low.

I installed the GoWesty gauge for oil pressure. I think the gauge is okay. The oil light does not come on at warm idle. the gauge reads 9 to 11 psi at warm idle.

The oil pressure was lower (I think) when the oil level was overfilled.

Even though I screwed up by not replacing the bearings, I'm having difficulty understanding why each cylinder's pressure (compression) is low. Why all 4?

Thanks.

[AtlasShrugged]

If you are certain you pre-set the valves correctly..then squirt some engine oil in the spark plug holes (spark plugs removed) and check the compression "wet"

If your 40/70psi cylinders now go up to 140psi..you have a piston ring/piston/cylinder problem.

If the compression numbers don't change much..say 50/90psi..then you have a valve/valve seat problem. Or..a bad compression gauge.

If you have a main/rod bearing problem..your oil pressure would be very low when the engine is hot at idle. 9/11psi hot idle oil pressure is pretty reasonable. 20/22psi at highway speeds seems pretty weird (low) compared with the hot idle psi.

What viscosity oil are you using? a 5w30 might give you the weird oil pressure numbers..use a 15w40 or 20w50 (in a warm climate)

[nacradriver]

Not to be insulting, but did you prime the oil pump and more important fill the oil filter up with oil before installing?
_________________
Güdrun -1989 Westfalia - 2013 - 2018
Petra - 1985 Vanagon - 1985 to 1991
Zisa - 1974 VW Van "Bus" - 1974 to 1985

[biondic123]

nacradriver: at this point, I'm not insulted, and am trying to learn and find out the root cause of my issue with the motor.

I did prime the pump, but not the filter. I'm assuming 2 things with the filter: 1. it would prime when the pan was filled, and 2. the motor performed without issue for 360 miles. Plus I cranked the motor a few times with the coil wire pulled off so it wouldn't start before I lit it up for the first time.

[biondic123]

AtlasShrugged: Thanks.

The heads are new, and the clearances were checked before starting the motor. If I recall correctly, the valve clearances were set to 0.006".

I like the idea of the "wet" test and will try it tomorrow. I agree the gauge could be faulty only because all 4 cylinders are measuring low, but it's a relatively new gauge. I'll check things out tomorrow and report my findings.

I also agree that the highway pressure was weird. I think it was higher when the oil level was lower (within the stick limits), but can't swear to it.

The oil in there now is 20W50 conventional. I was getting ready to switch to synthetic (also 20W50) when this problem cropped up so I'm holding off until, if and when I can get the motor running again.

[AtlasShrugged]

If you set the valve clearances at 6 thou..well that won't work with hydraulic lifters..they need to be pre-loaded..and that would explain the compression numbers being low..and might explain the weird oil pressures, maybe.

As each cylinder is pulled to TDC with the valves closed (remember, there are 2 TDCs: one with valves closed (compression stroke) and one with valves open), adjust the screws so they just touch the valve stem with the free-play taken up. Then adjust them in (compressing the lifter) another 1/2 to 1 1/2 turns. If everything is really bled, this may open the valve a bit until the lifter bleeds excess oil and adjusts. Then tighten the lock nut. (VW originally said compress 2 turns, but if it starts out with a bit of air that can over-compress.)

Remember, it's not unusual for a 2.1 to have valve clatter when the oil drains out of a lifter, and that can continue for some time until it fills and gets rid of air bubbles. That takes getting the oil hot and thin. There is much less trouble with clattering lifters when using a thinner synthetic, such as a 5W40, if the engine wear will give adequate oil pressure.

[dobryan]

For those that know (not I), at what point in a 2.1 can you overfill the oil so that it makes contact with the crank and froths, which could cause low oil pressure on the highway?
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[biondic123]

Atlas Shrugged:

Having the 0.006 inch clearance probably explains why the motor sounded a little louder to me than it should have; one lifter near cylinder one was particularly louder than the others, not air bound though (I don't think). I can certainly adjust the valves as prescribed by you. However, I'm having difficulty envisioning how having a little clearance would lower the compression. In my way of thinking, having the clearance would allow the valves to close more tightly (for lack of better terminology) creating satisfactory compression on the compression stroke. On the other hand, if the clearance were removed, or tightened to much, the valve might be prevented from closing causing lower compression. What's wrong with my way of thinking? My guess is it has to do with the hydraulic lifters being somewhat self adjusting. Many thanks for your time and patience with me!

As for the oil pressure, I think I'm going to have to suffer until I rebuild again and replace the bearings and crank (again) provided I can get the motor fired back up.

[biondic123]

AtlasShrugged:

I think I just found the answer to my question. If the cylinder can't get air, then it can't compress. Correct? In other words, if the input valve doesn't let in enough air, then there isn't enough air to compress. Ergo, low compression values. I hope this is correct, and the problem. If so, I have renewed hope.

[AtlasShrugged]

yes the hydro lifters are self adjusting..by not pre-loading the hydro lifters they never open the valves fully..really never open much at all..and compression numbers will be very low.

The snap ring retainer in the top of the hydro lifters body is under a lot of strain and energy as it is not designed to stop the lifter in operation..due to the designed in pre-load..the snap ring itself can come loose and cause some damage to the lifter bore and the lifter.

The hydro lifters also never "pump-up" and may be bleeding oil pressure too.

Reset the valves per the book and see what you have after a drive.

[AtlasShrugged]

[Howesight]

The valve lash is a good thing to chase. What was the piston deck height when you assembled the engine? It should have been 0.040"

Your rings might be installed upside down. They do not seal properly when this is done. Assuming that is not the problem, however, DO NOT use synthetic oil for the first, say 3,000 miles. It prevents the rings from seating properly.
_________________
'86 Syncro Westy SVX

[morymob]

When u do comp test make sure u prop open the throttle.

[biondic123]

Well, I had high hopes going into this valve adjustment routine, but things don't feel good.

Rather than get things too far out of whack, I only adjusted the valves on cylinders 3 and 4. With the valves adjusted for 1 or 1-1/2 turns, the compression is zero(0). I can get back to 60 psi by adjusting them for less than 1 turn. What is the significance of the above finding? The motor still won't start, or even sound like it wants to start whether the valves are set to 1/2, 1 or 1-1/2 turns on cylinders 3 and 4.

I have spark, and pulled the injectors out on the 3/4 side and they are spraying nicely.

I'm thinking maybe I should try the "wet" test next with the valves adjusted for 60 psi. Would this be a worthwhile data point at this juncture?

I don't have a nice, warm fuzzy feeling about this. Help is appreciated.

By the way, I did prop the throttle body open (AFM disconnected) on the oft chance it was restricting the flow of air during the compression test.

As for deck height and upside down rings. The 2.2 kit I purchased came with the rods torqued to the crank and the pistons with rings already inside the bored out cylinders. So, deck height was not measured by me and I'd be surprised if the rings were upside down since this kit came from a reputable supplier. Plus the motor ran great for 360 miles.

[biondic123]

Sorry guys and gals, here's some additional data.

So, I did a "wet" measurement on cylinders 1 and 2. This is the side where I have not disturbed the valve clearances yet. Cylinder #1 went from 80 psi to 90 when "wet". Cylinder #2 went from 70 to 80 psi when "wet". It was difficult to spray the oil into the cylinder. I used HD-30W with a small plant sprayer and must have gotten some in the cylinders since the pressure did go up a little.

Also, I checked my compression gauge with my air compressor and it matches up at 80 psi and 40 so I feel quite certain the gauge is good.

I'm not sure what to try next. Please see posting immediately above too and advise. Thanks for all!

[Ahwahnee]

[onslowb]

Can you tell us exactly how you are adjusting the valves.
_________________
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1970 Vw Bug SP 1600

[biondic123]

More data:

Performed "wet" test on cylinders 3 and 4.

#3 went from 70 to 110 psi
#4 went from 68 to 85
Tried to start it after the "wet" test thinking it might fire up with a little more compression. It DID NOT, and still will not start.

Can any conclusion be drawn from the data I've collected and presented so far?

Thanks.