Help: Bad compression. What to do?

[VWunderbaum]

My 1.6 suffers from very bad compression, I do not know what else it can be.
It will start, given enough gas, but it fumes terribly. Yesterday evening the smoke seemed bluish, this morning white... I have not tried to drive it yet, but I suspect loss of power as well.
It was driven with no oil pressure until it rattled and stopped by itself.
What I have done is to change the bearings on the crankshaft and pistonrods, and put new rings on, the pistons themselves were not seared.

I did measure as well as I could in all the the cylinderwells using a pistonring and measuring the gap and cross-section of the ring. Wear should be within 0,1 mm as according to the manual, BUT, when one turn the engine by hand, one can hear air slipping down. I do not know how much compression loss these engines normally have. Air slippage happens on all the travel.
The cylinderwalls have no vertical scratches, only subtle traces of diagonal ones, which are probably due to the honing done some two years ago when the wells were bored up to 0.1 oversize during a professional restoration. There are no pits or discoloring either.

What to do, any ideas?

Daniel

[tlbranth]

Did you do anything with the valves? It sounds like you guessed at the ring size which isn't a good idea and it sounds like you didn't hone the cylinders - also not a good idea. Did the cylinders have a ridge at the top? How thick? Did you remove it?
It sounds like you replaced the rod bearings and main crankshaft bearings. Is this correct? Did you measure the crankshaft journals?
For a lot of the measurements, you can get a pretty good idea with a halfway decent caliper.
_________________
Terry

1991 Westfailure. 2004 Forester 2.5 engine. 4speed Standard transmission.

[VWunderbaum]

Hey Terry, thanks for your reply. Your suggestion to hone the cylinders is a great idea. I have already ordered the bit.

About the valves, I cleaned them and they were all tight (turned the head upside down, then checked for leaks by pouring WD-40 on top of them)

I bought new pistons (just in case) with already mounted rings, all oversize +1.0 mm. I did not remove a ring to test the fit, not wanting to risk bending them or scratching the piston itself. I assumed the rings were as good a fit as could be.

About the bearings, I got the factory crankshaft journal measures, and mine are equal, so I bought std size bearings.

What is a ridge? Do you mean the fact that the cylinder is tapered? (tighter at the top were the rings do not arrive) This is the case for me, but the difference is very small, say under 0.1 mm. Otherwise the walls are smooth.

Do you suggest I get bigger rings and file them down to size myself? Leaving a 0.3 mm gap? I will dismantle the engine again and check my rings to see how much of a gap they leave.

[Wildthings]

If you have much of a ridge, you will damage the rings and pistons as they reach the top of their travel and the rings hit the ridge. Though if you could remove the piston out of the top of the block the ridge probably isn't too bad. You can get a ridge reamer to cut away the ridge if it is excessive and you can use a bar hone on the cylinders to cut away a more minor ridge.

Yes you need to hone the cylinders to get the rings to seat. I would at leasts remove a few of the top piston rings and check the end gaps at various locations in the cylinders. If the ring gaps are too small the rings will bind when the engine gets hot.

[tlbranth]

Cylinders wear most at the top and not at all at the bottom. So they taper as they wear. It's the rings that cause the wear and it stops where the top of the first compression ring (top ring) reaches TDC. This leaves an unworn portion of the cylinder at the very top. As Wildthings stated, if this ridge is not removed, it can break the new top ring. Ridge reamers can be rented or borrowed. I'm concerned that you put in oversize pistons and rings without knowing if the cylinders had been bored oversize. If they were standard size but just worn a bit, you would still use standard size pistons and rings.
Rings generally need to be gapped too. This involves squaring the ring in the unworn lower part of the cylinder and measuring the gap between its ends with a feeler gauge. I'm not familiar with your engine so I couldn't give you a number but it should be in your shop manual. An air-cooled engine will have larger gaps than water-cooled.
To hone the cylinders, you can either buy a tool or make one. I use a piece of 1/2" dowel with a kerf cut 2" or so lengthwise and a piece of emery cloth doubled over and stuck in the kerf. Chuck it in a drill and move the thing up and down the cylinder while it's turning 'til there's no shiny spots left.
You ought to remove the valves and inspect the seating surfaces. Based on what you see, either get the seats recut at a machine shop and the valve faces reground ...... or lightly lap them. If your intake valves have stem seals, replace them. Check that your valve stems don't wiggle around much in their guides. If they do, you could need new guides, valves or both. This could be a source of oil getting into the combustion chamber and making blue smoke.
_________________
Terry

1991 Westfailure. 2004 Forester 2.5 engine. 4speed Standard transmission.

[dobryan]

I'd recommend a leak down test to confirm what is going on.
_________________
Dave O
'87 Westy w/ 2002 Subaru EJ25 and Peloquin TBD

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[?Waldo?]

[VWunderbaum]

Thanks Wildthings.

I have removed one piston and checked up and down with the top ring. The gap is a perfect squeeze of 0.3 mm all the way. So I am optimistic that after the honing compression might be better.

I have only opened one cylinder today, I don't want to mix the pistons up so I will remove them one at the time when the device arrives and I can start the job.

[VWunderbaum]

Hey Andrew
Thanks for your input. I did not want to confuse anyone, I never knew there was a 1.6 liter aircooled petrol.

My manual says 0.1 is the wearlimit beyond the initial cylinder bore, which in my case is 1.0 mm oversized, not 0.1 as mis-typed in the first post.

[?Waldo?]

Ok, so now everyone knows we're talking about a diesel. Good to know.

I don't know where you are finding the 0.1 wear limit spec or what spec that is referring to. Are you looking at the Bentley? Are you talking about piston to bore clearance?

In the Bentley, 13.29 at the bottom right corner.
Piston to cylinder clearance for new parts is 0.03mm (0.0011")
The wear limit is 0.07mm (0.0027")

Bear in mind that is the difference between the piston diameter (at the bottom of the skirt) and the largest diameter anywhere in the bore (near the top but below the ridge if there is one and perpendicular to the crank).

Your method of using a new ring and measuring the gap to try to figure if your bores are out of spec is not a viable measurement. The ring gap is a different measurement to take on reassembly. To determine if your bores are worn out you should be using either a bore gauge or a snap gauge combined with mic.

[fxr]

[Terry Kay]

First post , first sentence identified the engine.

1.6 is an oil burner without reservation.
_________________
T.K.

[crazyvwvanman]

Since he didn't post his location there was a least a chance it was a 1.6 aircooled T3, gasoline. They produced them for 3.5 years, not sold in USA/CA.
VW Parts Data says they built 143,000 vans with the aircooled 1.6 gasoline engine.

Mark

[tlbranth]

Sorry all. Don't know that much about VW's and assumed we were talking about a gas engine. So I'll bug out of this one since I've never worked on a diesel.
_________________
Terry

1991 Westfailure. 2004 Forester 2.5 engine. 4speed Standard transmission.

[VWunderbaum]

Success!

This van rolls again


Thank you for your advice and help. It is beautiful that this community is so active and full of knowledge.

I just came back from the first test drive and power is like my 1.6 TD of before, there is no smoke, just a little smell at the startup (but not upon revving it as I parked it at the end of the ride), this might get better as the rings set themselves.

In a downhill I shut of the engine, put it in second and let the gravity jerk the car forward through the four compression-cycles. Three were equal and good, one was a bit faster and not that tight. At this point I don't think I bother to open it up again and hone it. I will see how it continues to perform.

About the measurements, sure I would like to have the proper instruments, but using an old ring at various depths in the cylinder, and a feeler gauge to measure the gap, then close the ring shut under a vicegrip and measure diameter sideways and lenghtwise (as the ring is a slight oval) gives a fair idea of the diameter I think.
As circumference = diameter x 3.14, I divide the gap in the ring with 3.14 to see how much to add to the diameter of the cylinder.

Hey Andrew
The 0.1 mm wear limit I have from a book called 'Reparatur Leitfaden Volkswagen Transporter' it is the 1991 edition published by VW for their serviceoffices.
It is in German, but you will find the wearlimit beyond original cylinderbore on top of page 30. If you contact me here; [email protected] , I will send you the pdf if you are interested.

And yes, I am right at the limit so we will see how long it lasts. But for now it is a joy to speed up the hills again in my Wundervan since 15 years.

Cheers and thanks again