Poor compression on all 4

[jgallen]

Helping a friend restore his 59 transporter with 36 HP engine

He put it all back together and after a failure to start (didn't even sputter), checked compression and all were under 25 psi. Bummer.

Trying to figure out why, valves are all adjusted and close fully. Haven't checked rings yet.

Copper crush gasket between cylinder and head don't seem to be very crushed after appropriate torquing (27 lbs). There is only a slight mark on them (compared to the prior which was obviously smushed). New heads were used (with same SN as prior) but old cylinders.

Could this be the cause of that low of compression? with a bit of oil down the cylinder we could only get 50 psi.

Any help MUCH appreciated.

[sub-hatchtim]

Did you orient the rings correctly?
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[BarryL]

Are you saying that you pulled of a head to look or are you going by peeking from the outside at the gas ring?

[FarmerBill]

Was this a full rebuild? Just heads? Is there something interfering with the head seating on the cylinder? What did you set your compression ratio at? Valves can be closed but still leak. Try a leak down test and you might be able to hear where you're losing compression.

[jgallen]

This was a full rebuild. Had a bent push rod but no other obvious damage.

Heads have been pulled to try to find the source which is how we were able to examine the copper gaskets. We were able to use Prussian blue with a new set of gaskets which is how we know there is very little downward force on them (just the lightest trace showed up).

We also blued the very end of the cylinders to see if they seat correctly in the head which it does. (BTW is most of the "fit" to sustain pressure done by the top of the cylinder contacting the head or is it due to the compression of the copper gasket? (newbie question admittedly).

One obvious possibility is to take a few thou off the top of the cylinder head to allow more compression on the gasket.

Don't have the cylinders pulled from the case so hard to say about the rings. it will be interesting to see where they are oriented.

[RWK]

check the depth of the cylinder head where cylinders sets,,possible the cylinders fin area and ledge is touching the head not in the recessed seat or pocket. there should be clearance here at least .01 or more, you are on the right track checking with blue.
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73 Type 181
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[FarmerBill]

Don't take any material off of anything in the cylinder to head mating area until you determine your compression ratio. The cylinder to head to seal takes place at the top edge of the cylinder and the flat inside the head, the gasket is just a soft material in between to take up any inconsistencies between the surfaces and ensure a good seal. The "crush" of the gasket is also important in determining your CR, if your'e not getting good crush on your copper gaskets you are effectively lowering your CR. Like RWK said, you probably have cylinder fins stoping the head from fully seating. (still check your compression ratio anyway).

[jgallen]

With this type of cylinder how would the fins interfere with the mating of the cylinder to the head? I am getting good contact where the black arrow is on the image based on the Prussian blue.

Back to my main question which I am still confused about as I am seeing different answers. Is the rim of the cylinder where the arrow is, the location where the compression seal takes place or is it the base where the copper gasket where the majority of the seal takes place.

Thanks

[FarmerBill]

Ok, I just realized you are not talking about a copper head gasket correct? The copper gasket you have goes around the outside of the cylinder not on top? If this is the case then yes, the sealing surface is the narrow edge on the top of the cylinder to the inside of the head. The gasket I believe you are referring to is sort of an auxiliary seal they put on stale air engines to keep an exhaust leak from getting into the heating system and giving everybody carbon monoxide poisoning.
Here's a thread that explains how it works.
https://www.thesamba.com/vw/forum/viewtopic.php?t=704350&highlight=copper+gasket
If you look about halfway down the page on the thread I linked you will see a diagram. The red arrow is the cylinder to head seal, the black arrow is the copper gasket I think you're talking about. If the head can't get enough pressure on the top of the cylinder to seal then you will never get good compression. Try torquing the heads down without the copper gasket and see if that gets you where you need to be. If it works then you found your problem. Then you just need to re-assemble with a thinner or softer gasket. If, like you said you think that you're already getting a good seal between your cylinder and head then the problem lies elsewhere.

[BarryL]

If you crank it and put your hand over the oil fill do you feel pressure? I realize you can't do it with the heads off. Are you doing the compression test with the other 3 plugs out?

[Busted-bolt]

If this is a stale air forty horse you are talking about .Are you using oem VW stale air auxiliary sealing rings ? I have not found a good source for new aftermarket ones yet. The aftermarket ones "non VW" ones will not "crush" to conform at all and will hold the cylinder top barrel surface away from seating on the head.I tried to crush a pair of those aftermarket ones on a exploded block and I ripped the head studs out before they even started to "dent". You must buy nos VW ones or carefully remove the old ones and reuse them. You run the risk of the used ones not sealing very well either. You will at-lest have the cylinder mating to the head properly.This may not apply here but this is what i have ran on to in the past.
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I do all my own work,body,engine and transmission.

[FarmerBill]

I wonder if you could anneal them? I bought a box of nails the other day that were soft as butter, modern manufacturers seem to have forgotten how to heat treat metal. Or maybe the aftermarket rings are the wrong alloy. Disappointing when the simplest of products don't meet expectations.

[Busted-bolt]

Yeah it may be posable to soften the brass that way .The original VW ones are so thin you can almost dent them with you're finger nail and they have a fiberglass or asbestos packing. The after market ones uses a way thicker brass source stock sheet metal with no packing, the ring itself is also way thicker to. There is no place for all that extra metal to go when it is placed between the barrel and the head.
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Vw collection 60 combi ,61 panel ,62 deluxe micro,82 diesel Westfalia,88 Vanagon synchro,98 Jetta tdi,11 Jetta tdi mt ,11 Jetta tdi dsg.
I do all my own work,body,engine and transmission.

[jgallen]

Update!
The apparent cause after much disassembly and reassembly and some machining work is that the top of the cylinder was not mating with the head completely.

We found this using Prussian blue. After milling the top of the cylinder flat and then lapping the cylinder into the head we were able to get good contact and normal numbers using a leak down tester.

Also found using the leak down tester were intake valves that weren't seated well despite lapping originally and we are in the process of re-lapping them.

Thanks for all the help!.

[jgallen]

Well, It has been a crazy last 6 months. Put the engine on hold as we were making no progress with the poor compression (which it turned out was not fixed and we STILL have low compression) so are now back to square one.

Changes we have tried:

1. new pistons (64mm stroke), rings, and cylinders (77mm) (no help) (yes the rings are staggered)
2. changed how we ground the valve seats (bought neway cutters now for 3 angle valve seats) (and build a jig where, after cutting the new seats and lapping, we bolt the heads to a flat piece of aluminum with a rubber gasket and were able to determine the valves are not leaking) using a leak down tester.
3. We actually bolted a block of extruded aluminum to the top of both cylinders, drilled and tapped at hole the same size as a spark plug, without the heads and found they leaked (meaning that the cylinders were not level with each other) so we:::
4. Fly cut the heads to be within .001 of each cylinder and clean and shinny.
5. For the heck of it we machined the deck of the case on the mill (it only needed less than 0.010 inch to get them all cleaned up).

(We volumetrically measured the heads and found they hold 47ml (pretty close to the specified volume and a deck height of 0.044 inches for a compression ratio of 6.7:1)).

Using the leak down tester we get "moderate" leakage (which is better) but BUT STILL GETTING 25 PSI on all 4...

What a bummer.

So we are still scratching our heads... I noticed that JBugs video rebuilds a 36 and the cylinder head bolts are HEX style (and large). Is there any way that using smaller bolts and washers (bolts are 15mm I think on 10mm studs) could be stopping the heads from tightly sitting on the cylinders? We torqued each of the 8 bolts to 24 psi.

Any ideas appreciated. Suffering from engine rebuilding fatigue....

thanks

John

[Tvättbjörn]

Piston rings usually have a top side. TOP is etched onto it. Marking has to face the cylinder head.

Camshaft installed correctly? It can be off by a few teeth before valves hitting the head.

[Tvättbjörn]

[jgallen]

PostPosted: Today 7:40 am Post subject: Re: Poor compression on all 4 (update) Reply with quote Edit/Delete this post Delete this post Report this post to Moderator/Admin.
Thanks for the reply. Yes sorry Nm.

The rocker arms are not on so all valves are closed (new springs).

The rings are oriented correctly.

The cylinder head is not loose to the touch..

The pistons came with rings (not already installed) so we gapped them appropriately and double checked them.

I do not hear a hissing sound from heads.

Cam shaft 0 between the two dots (just did it yesterday and double checked)

Bought a second compression testing kit to verify the first one.

When we pressurize the cylinder I DO hear pressure going into the case but figured that was just normal blow by past the unseated rings. How much should you be able to hear on a new rebuild with unseated rings?

Anyway thanks for the help!

[Abscate]

You will have to start again from tear down , but this time critically evaluate every part in the engine. The days where you can buy parts for these on spec are gone. It’s common to get new out of box stuff that won’t work

24 No for head studs? That sounds way light, but I don’t carry those numbers in my head.
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[Lind]