Low compression...

[MidWesty79]

Hey all, i’m starting a 3 month voyage to Alaska. Departed WI last week and I’m doing some tune up work at a family member’s place in WY. I did a quick compression test while changing plugs and noticed my #3 cylinder is at 77psi, the rest were around 92. The engine wasn’t super warmed up, but I did let it idle a few minutes before testing.

I rebuilt the engine about 5 years/40k miles ago including rebuild heads from Adrian at Headflow masters with bigger valves and Heavy Duty Stainless Steel valves. It had a sunk valve prior to the rebuild.

I checked the valve adjustment (hydraulic) and didn’t see anything crazy.

My question is, is the valve sunk again? I have about 10-12k miles ahead of me.

Thanks!
Nick
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1979 Westfalia, 1975 BMW 2002, 1996 Mazda Miata, 1979 Jeep CJ5, 2006 325 XI Wagon, 2021 M240i (all manual transmission... as god intended.)

[busdaddy]

Time to pull the rockers and put a straightedge across all the valve tips.
only 9' lbs torque on the rocker shaft nuts when you put them back
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[MidWesty79]

Just checked with a straight edge. I didn’t use a feeler gauge or anything, but they appear to be dead level.
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1979 Westfalia, 1975 BMW 2002, 1996 Mazda Miata, 1979 Jeep CJ5, 2006 325 XI Wagon, 2021 M240i (all manual transmission... as god intended.)

[MidWesty79]

Smallest feeler I have with me is .006”. I couldn’t get close to getting it under the straight edge at any valve.
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1979 Westfalia, 1975 BMW 2002, 1996 Mazda Miata, 1979 Jeep CJ5, 2006 325 XI Wagon, 2021 M240i (all manual transmission... as god intended.)

[SGKent]

Your best bet at this point is to put a leak down tester on it and see where the compression is going.
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[MidWesty79]

Fed the cylinder 30-40 psi. No air out of the exhaust or intake. Breather had a fair bit of air rushing out. Rings are going I suppose. Anyone have any “magic elixer” recommendations?!
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1979 Westfalia, 1975 BMW 2002, 1996 Mazda Miata, 1979 Jeep CJ5, 2006 325 XI Wagon, 2021 M240i (all manual transmission... as god intended.)

[Tram]

[Wildthings]

Considering that you are likely around 7000' above sea level your number are not that bad. I would at least try adding a full quart of upper cylinder wall lubricant to your fuel for a few tankfuls, MMO, Sea Foam, 2-cycle oil, or synthetic motor oil.

According to the Vanagon Bentley 85 psi is normal at seal level for a 2.0L aircooled engine and 73 psi is minimum while the max difference between cylinders is 44 psi. You are way better than that.

Heading out onto a three month trip would make me a bit more concerned though.

Corrected for a 7000' elevation your number would look more like this

Compression for three cylinders: 114 psi
Compression on one cylinder: 95 psi
Difference between cylinders: 19 psi

A synthetic oil will keep your engine cleaner inside than a dino oil.


When doing an compression test, you need:

A well charged battery
All plugs removed
Throttle held open

[Tcash]

Could be stuck rings.
Might be worth putting a couple of table spoons of Marvels Mystery or Trans fluid down the spark plug hole, turn the engine over a couple of times wo/strarting to spread it and let it soak over night.
With the spark plug out, crank the engine a few times to clear the cylinder. Install the plug, fire it up and bring it up to operating temp, then excel hard and use engine braking to decal hard to brake the rings free.

Good luck
Tcash

[MidWesty79]

I only had one plug out at a time, and didn’t Have the throttle open. I was mainly looking for big differences, not so much the actual numbers, but that would likely throw off the actual values.

I’m at about 6400 ft of elevation.

I always run Rotella 15w 40. I was told years ago on the samba that it was a good choice. Not sure if that wisdom still holds true. I change it every 2k miles.

I’ll try some seafoam in the tank and MMO down the plug hole, see if that gets me anywhere.
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1979 Westfalia, 1975 BMW 2002, 1996 Mazda Miata, 1979 Jeep CJ5, 2006 325 XI Wagon, 2021 M240i (all manual transmission... as god intended.)

[SGKent]

[Wildthings]

[MidWesty79]

I shot a bit of MMO down the plug and let it sit about an hour. I then drove the bus around, revved her up pretty good a few times and checked the compression again, this time with all the plugs out and the throttle open. I got 80psi on #3 right around 100 in the other 3.

I’m going to shoot some more MMO down the #3 and let it sit overnight. Take another look in the morning I guess.
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1979 Westfalia, 1975 BMW 2002, 1996 Mazda Miata, 1979 Jeep CJ5, 2006 325 XI Wagon, 2021 M240i (all manual transmission... as god intended.)

[Tram]

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[Tcash]

Good luck
Tcash

[aeromech]

Two things.

1). You’re betting a lot considering your destination is Alaska. Best to try another gauge to be sure.

2). Whatever happens be sure to make an adult decision and if you need to abort the trip and cut your losses then do it.
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[Davada66]

I would delay that trip. The compression reading should be around 135 to 140.

[airschooled]

[Wildthings]

15 year +/- ago I asked a question on Shoptalkforums.com and was advised that I should rebuild my engine before I drove out my driveway again. I ignored the advise and only got another 100K miles out of the engine. Should I have ignored the advise and canceled my family's trip to Mexico or not?

Jamb it down into third, put your foot to the floor, and enjoy life. You only get one time around. The best advise I every got in life was to buy a junker when you are planning an extensive trip so you will not have to worry about taking a major financial loss should you have a break down and have to abandon your ride.

[airschooled]