Lack of compression -1.9TDI (BLS engine)

Gobey

New member
Joined
Mar 9, 2014
Location
Auckland
TDI
Golf 5
My 2008 1.9 Golf TDI (77kw BLS engine) had a failure on 176,000 km and I thought it good to replace the rings, bearings, camshaft, cam lifters and injector seals with the engine open. I fitted standard rings and made sure that the rings face the correct way up. Did it all myself except the skimming of the head and valve seating which was done by a professional workshop. Also had to do the rocker adjustments to the correct measurements as per the VW Workshop manual.
On top of that I replaced the turbo (which comes a complete unit consisting of turbo, manifold and actuator) as the turbo shaft was broken. I did not adjust the actuator setting though.

The idling is now very inconsistently at low revs(800r/m). As soon as the revs pick up it seems to disappear. Took it to the local VW dealer for a check and they informed me that the compression is low (+-16bar/235psi vs normal compression of between 25bar/370psi to 30bar/440psi.....not sure if it is the correct measurement?), but that this consistent on all pistons. There is also a loss of power, as though the turbo is not really kicking in.

Any suggestions on what I could do?
 
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nord

Veteran Member
Joined
Mar 5, 2010
Location
Southern Tier NY
TDI
All turned back to VW. Now a 2017 Hundai Tuscon. Not a single squalk in 10k miles.
Unfortunately when so many things have been done to an engine it's somewhat difficult to sort things out. Let's start with the basics:

Rings... I assume you end-gapped them properly. I further assume that you made sure that the gaps were staggered and not aligned. TDI lower ends are tough and I doubt any problems there even if you did nothing.

Valves... Have they been properly faced and do they seal?

Injectors... Are they properly seated and sealed?

Once we're assured of the above, then I'd suggest a leakdown test for each cylinder. If your job was properly done there should be minimal leakage past the rings into the crankcase and no flow past the valves. (I'm not suggesting improper work. All I'm saying is that these things need to be checked.)

Assuming all is well as far as the above, then I'd question the head gasket. Very slight differences in thickness will yield much different compression ratios. My guess? You have too thick a gasket installed. (As I remember there is a choice of three thicknesses.)

Loss of power? Obviously low compression will cause a poor idle and power loss. If the turbo is working it will somewhat compensate and hide the root problem. Given that you have a new unit I'd check vacuum and related adjustments but only after you get the initial idle and compression problem solved.

So back to the gasket. Compression is reported as about the same for each cylinder. This means to me that either the same error was made across the board, or one error was made that affects compression on all cylinders. Unless you replaced rods or pistons with incorrect components there is really only one thing (other than leakage) common to the problem at hand.

Sorry I don't have a magic bullet to solve your problem. I'd tell you to bring the car over to our garage but I hear the trip across big salty might be a deal breaker.
 

newlitemotorist

Veteran Member
Joined
Jan 16, 2013
Location
Indiana
TDI
06' Jetta TDI dsg, 445,000 miles and counting!
Nord hit all of the main points but I would like to reiterate plus add some thoughts.

Check your compression with another tester just in case. Like nord pointed out, the rings have to be staggered or else you provide a straight path for cylinder pressure to escape past the piston. Another thing that comes to mind that wasn't mentioned is cylinder wall prep. Did you hone the cylinders with a ball hone? In order for the rings to have a better chance of seating it is important to have the proper finish which provides a good cross hatch.

Finally, what caused your failure in the first place? Did you measure your cylinders to make sure you were good to reuse your standard size pistons? Did you measure piston protrusion? I too would suspect the wrong thickness head gasket! Just throwing ideas at you, there are other more knowledgeable people on these boards that will surly to able to offer more insight.
Keep us posted
 
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Gobey

New member
Joined
Mar 9, 2014
Location
Auckland
TDI
Golf 5
Hi Nord & Newlitemotorist,

On advice from the cylinder head machine shop, I replaced the con rods with an aftermarket model. I did not check the piston protrusion though! I will have to redo the work done and check to see if the gasket is the right size.

Many thanks.
 

bl00tdi

Veteran Member
Joined
May 8, 2011
Location
Miami
TDI
None
Unless there was other appreciable damage to the cylinder wall I'm almost certain the crosshatch is fine at 109k. And remember its there for oil retention not ring break-in or sealing.

Before you tear into the engine, please verify that the cam-to-crank timing is on point. If it's off it could definitely affect compression numbers across the board. Also, were the pistons fitted into their original bores? Other than that I would also suspect the head gasket and injector sealing. A quick way to check the latter is to run the engine off of a jar of D2 or Diesel Purge and checking the tandem pump output hose for bubbles.

Side note: The BLS engine fascinates me as it's essentially a BRM with a DPF fitted. Gobey: How reliable have the DPF's proven themselves to be? Any issues?
 

newlitemotorist

Veteran Member
Joined
Jan 16, 2013
Location
Indiana
TDI
06' Jetta TDI dsg, 445,000 miles and counting!
Unless there was other appreciable damage to the cylinder wall I'm almost certain the crosshatch is fine at 109k. And remember its there for oil retention not ring break-in or sealing.
You make good points but I have to respectfully disagree with your generalized statement about the cross hatch. Your statement is only half true! You are right that its sole purpose is for oil retention but the reason why this is so important aside from lubrication is for the proper sealing of the piston rings. Too shallow and the walls hold too much oil preventing proper ring seal, too steep and the oil runs off too fast causing oil starvation and premature cylinder wall and ring wear.

Am I saying this is the cause of the op's low compression? Not really. I felt it necessary to mention since it is an important step ANY time you are replacing the rings. You have to have sufficient "valleys" for the oil to cling to or else the rings will wipe the cylinder walls clean with every stroke. At 100k miles I am sure the hatch is still visible but that doesn't mean it is optimal for a new set of rings.

Point being...it has a LOT to do with ring seal!!!
 

bl00tdi

Veteran Member
Joined
May 8, 2011
Location
Miami
TDI
None
A poor finish or pattern can prevent sealing or cause premature wear yes, but flex-honing a "used" cylinder is not necessary for proper ring break-in by any means. That was my point. Some people seem to think that it's good to rough the cylinder up a bit to give the rings something to "bite" so that it can wear in properly, when a bottle brush type hone does just the opposite. It's simply a final step to knock the jagged peaks off (plateau finish) after a proper hone job has been performed on a worn or bored cylinder. It's more of a finishing tool than a cutting tool. Further, an amateur with a drill using Youtube videos as a guide will probably do it wrong anyway and end up with something worse than the factory finish. Best to be done professionally using a full-on Sunnen (or equivalent) if the cylinder condition is so poor as to require refinishing. My guess is that it's not. Why try to fix what ain't broke?
 
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Ol'Rattler

Top Post Dawg
Joined
Jul 3, 2007
Location
PNA
TDI
2006 BRM Jetta
A rebuilt at 109K miles? Completely unnecessary. Something went wrong with your ill advised "rebuild".

What was the failure you had? If you honed the cylinders and installed standard rings, the bores might be out of spec for the new rings. Were the bores measured for diameter and taper after honing?
 

newlitemotorist

Veteran Member
Joined
Jan 16, 2013
Location
Indiana
TDI
06' Jetta TDI dsg, 445,000 miles and counting!
A poor finish or pattern can prevent sealing or cause premature wear yes, but flex-honing a "used" cylinder is not necessary for proper ring break-in by any means. That was my point. Some people seem to think that it's good to rough the cylinder up a bit to give the rings something to "bite" so that it can wear in properly, when a bottle brush type hone does just the opposite. It's simply a final step to knock the jagged peaks off (plateau finish) after a proper hone job has been performed on a worn or bored cylinder. It's more of a finishing tool than a cutting tool. Further, an amateur with a drill using Youtube videos as a guide will probably do it wrong anyway and end up with something worse than the factory finish. Best to be done professionally using a full-on Sunnen (or equivalent) if the cylinder condition is so poor as to require refinishing. My guess is that it's not. Why try to fix what ain't broke?
I see what you are saying now and I apologize for the misunderstanding. The flex hone is, like you said, a finishing tool and it is to be used as a final prep. I agree that at 100k the original finish is probably fine and in the op's case he should probably leave it alone. Your youtube comment made me laugh because it is so true.

If it were me, I would still run the proper grit ball hone to restore the final finish.

I too would like to hear what actually failed. Unless oil pressure was lost and bearings bit the dust, a total rebuild "just because" at 100k is completely unnecessary. Whats done is done at this point. I am still betting on the head gasket being the wrong thickness since he replaced the rods in the process and did not measure protrusion. From there, improper injector installation makes sense.

I could be wrong but wouldn't the timing have to be way off to effect compression in our case since these cams have negative over-lap? Just some more loud thinking...no claims.
 

bl00tdi

Veteran Member
Joined
May 8, 2011
Location
Miami
TDI
None
I see what you are saying now and I apologize for the misunderstanding. The flex hone is, like you said, a finishing tool and it is to be used as a final prep. I agree that at 100k the original finish is probably fine and in the op's case he should probably leave it alone. Your youtube comment made me laugh because it is so true.

If it were me, I would still run the proper grit ball hone to restore the final finish.
No worries. And your main takeaway is a fair-enough point. Just wanted to make it clear that it's very easy to mess up and be worse off.

I could be wrong but wouldn't the timing have to be way off to effect compression in our case since these cams have negative over-lap? Just some more loud thinking...no claims.
If the cam is retarded by one tooth the intake valve will close late, lowering the dynamic compression. I'm wondering if the exhaust valve would touch the piston at the top of the exhaust stroke though..
 
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