2003 XC70 - Low Compression after head rebuild Topic is solved

wieselaj · Post by **wieselaj** » 24 Mar 2018, 05:53

I would appreciate any help on this topic as I am running out of guesses. Keep in mind... I am just an avid DIY'er, this is an extra vehicle that I have owned for a year and only have about $3K into. My (perhaps shortsighted) philosophy has been to either keep a really tight budget or to move on from the car.

Background
2003 XC70 w/ 116K miles
I bought the car a year ago and almost immediately had the timing belt changed by my father
Drove the car for 6000 miles or so essentially trouble free. No oil burning, smoke, or coolant burning.
Two months or so ago, the car threw a cam sensor code. Was running smoothly so I (incorrectly) assumed that I had a faulty sensor
Changed sensor, cleared code and drove for a week without problems or new codes.
I did have to add a small amount of coolant around this time. That's the only time I ever had to add coolant. I think it's unrelated, but....
Wife drove the car - check engine, loud, no power.... dead
Car was towed to mechanic who said that the timing was way off and that he couldn't get compression. His advice was to junk it.
I do not know why the timing slipped. The mechanic said that the crank bolt was missing. This is odd because my father said that he didn't remove the crank pulley, he removed the lower bracket and slipped the belt through the gap.
My suspicion is that the tensioner bolt loosened over time as I found anti-seize on the threads.
I had been wanting to try to rebuild an engine so I had the car towed to my house and I pulled off the head.
It was evident from the top of the cylinders that the exhaust valves had been hit but not obvious from the valves themselves. The headgasket was fine.

I cleaned the head, removed the valves and seals, and could tell that roughly half of the exhaust valves were bent.
I ordered a head gasket kit, all new osvat exhaust valves, new valve seals, cam locking tool etc. I did not send the head to a machine shop.
I lapped the exhaust and intake valves, replaced the seals, cleaned the top of the pistons w WD40, cleaned the PCV system and replaced hoses fittings as needed, and began reassembly.
The crank seemed to spin fine and the timing mark on the crank corresponded to just a tooth or two shy of top dead center on cylinder one.
As I mentioned, I bought the cam locking tool so I wasn't worried about timing the cams. With the cams locked, and the VVT gears rotated clockwise to limit, the timing marks on the cam lined up with the cam cover. (I never removed or loosened the VVT hubs)
Timing set, cam locks unbolted, I had no problems rotating the engine clockwise via the crank bolt.

Here's the prolem... the car will not start. It cranks but will not start.
I thought it was spark... We checked all the plugs and they are firing. Oddly, the plugs were not getting wet.
So it must be the injectors. Node tested the injector wires and they were firing. fuel rail was pressurized and gas would release from the shrader valve. We eased the right side of injectors out of the intake and turned the car over and we could see the gas.
Checked compression. ONLY 60-65 PSI IN EACH CYLINDER!!!! (Compression test gauge, all plugs removed, max throttle and rougly 8 spins of the motor)
It will wet test higher... some over 100 PSI if tested wet.
But why would ALL of the rings have gone bad when the car had been running fine before timing slipped!?!?!?
I injected about 20 PSI of compressed air into all of the cylinders (with each cylinder as close to TDC as I could estimate via a zip tie through the spark plug hole) and it really only seemed to be escaping from the dipstick, the PCV breather hose and nipple, and oil fill.
i could not feel air coming out the tail pipe or through the vacuum connection on the intake.

More to consider....
I asked my mechanic what he thought and he thinks it's likely that the pistons/rings are fine and that I still have a timing or valve train issue. He thinks I should pull the head off and take it to a machine shop. I don't know how this would jive with my crude leak test.
My father is suspicious of the copper coat that I put on the head gasket. I will note that I didn't see any bubbling in the coolant tank and it would seem to be a stretch for the air to escape through the head gasket and find away into the crankcase or cam cover without bubbling the coolant.
I am wondering if I have the crank off by one turn. I don't see how this could be an issue but I read another thread on here about a lack of compression after a timing belt change and the OP resolved his issue when he remembered that he only "turned the crank one turn instead of two".

Any help would be appreciated!

Adam

Post by **RickHaleParker** » 24 Mar 2018, 08:37

Did you measure the head and block deck for warpage? .....

Post by **chrism** » 24 Mar 2018, 09:08

Sometimes the cylinder walls and rings can get dry and not seal well. You could dry squirting some oil into the cylinders and see if it improves compression. But the fact that ALL cylinders are low on compression by the SAME AMOUNT suggests that one or both of the cams are way out of time and keeping a valve open too far into the compression stroke.

wieselaj · Post by **wieselaj** » 24 Mar 2018, 09:17

Thanks for the replies. I did not measure for warpage. I wasn't very worried about that since I didn't blow the head gasket and I don't have any confidence that I own anything straighter than the cylinder head. I also had read enough threads about these heads sealing with some degree of warpage. Perhaps that was a mistake, but I don't think I have any indication that it's the head gasket that is leaking.

A couple of other things that I thought of.... The mechanic had asked me if any water or coolant had collected in the cylinders. The block was open for 4-6 weeks, but it was covered. I am wondering though if my attempt to clean the cylinder top caused me to clog/stick the cylinder rings.... if the crud that i was scrubbing off ran down the cylinder walls. I just pulled the plugs and dumped a can of sea foam in the cylinders to see if that helps. I will rotate the engine every half hour or so to see if I can free up the rings.

I will go take pictures of the timing marks and post them. I didn't have the benefit of being able to set the timing before taking the belt off, but I believed that the cam locking tool would keep me in the clear. Maybe I have missed something....

wieselaj · Post by **wieselaj** » 24 Mar 2018, 09:34

Well... I am wondering about the timing. I will show pics of the front of the engine. Where - to my eyes anyway - it looks like the timing gear is perfectly aligned at the cams and the crank. On the back of the engine though... the slots on the cams aren't parallel to the seem of the head or to each other. I am guessing that is due to the rotation of the variable valve hubs, but is that what should have happened? The cams were locked from the back when the belt was installed with the cam gear aligned with the cam cover.

wieselaj · Post by **wieselaj** » 24 Mar 2018, 09:41

Let me post a clarification/correction here... The pics of the front and rear of the cams above were taken after I had rotated the cams past the alignment marks by a quarter turn and then backed up to alignment. I just went back down and rotated the engine clockwise to the alignment marks (no turn past and then back) and the slots at the back of the cams are now perfectly parallel with the seams on the head.

Post by **firstv70volvo** » 24 Mar 2018, 11:33

Hi Adam,

I tend to agree with the mechanic, I don't think it's your pistons/rings although I don't agree you should pull the head off just yet. The compression readings are very low but also very consistent so incorrect timing is most probable cause in my opinion. If it were a head gasket or valve sealing problem I just can't see how you'd get the consistent low results for every cylinder and your compress air results help confirm this.

You mentioned the crank bolt was missing and if it's the main center nut that was missing then that's an area to check again. I think it would be difficult to damage the crankshaft timing belt pulley internal splines even with the missing crank nut but it's something I would check because everything else appears to look good with regards to timing. The mechanic could have also meant it was missing one of the four serpentine belt pulley bolts, which I wouldn't think would cause any any damage to the timing belt pulley. If it was the center nut that was missing though I would pull the crank serpentine belt pulley off and check the crank timing belt pulley, the splines of the pulley and crankshaft, is there any back and forth movement of the pulley (timing belt loosened or removed) or any other obvious damage to the pulley such as worn belt teeth. Seems unlikely the pulley could be damaged this way, it's a robust design, but worth a check.

You're leak down test results and compression results after adding oil point to poorly sealing rings but the consistency of the low readings and previous good running condition just doesn't add up to sudden piston/ring sealing problems. Double, triple check everything timing related first is the way I would go.

some good information here
https://www.motor.com/magazinepdfs/081999_05.pdf

Post by **firstv70volvo** » 25 Mar 2018, 10:43

Just a follow up of my previous post and an example of possible crankshaft timing belt pulley spline damage and in your case considering the crank pulley nut may have been missing.

different forum site but good photos of pulley spline damage
https://volvoforums.com/forum/volvo-s80 ... ear-89394/

wieselaj · Post by **wieselaj** » 25 Mar 2018, 13:04

I let the seafoam sit in the cylinders for about 24 hours and tried the compression test again today. No change. Every cylinder measured right around 60 PSI dry and roughly 95-110 PSI wet. Certainly a big jump. I have read that if pressure jumps more than 10% than its probably the pistons/rings. Odd to me that the all the cylinders would have the same reading though. Also, odd that it seems to be a sudden onset... I mean 60 PSI is ABYSMAL. I also don't know how much that the fact that the engine is completely cold is influencing all of this. Maybe I am losing 40 PSI because of worn rings and the other 50-60 PSI is getting lost in the timing/valves.

As for the crank nut... The mechanic originally told me that I had been missing a bolt on the crank pulley and was asking me why it was missing when the pulley doesn't have to come off to change the timing belt. When I took the car home, the pulley, cam covers, stablilizer bar, etc was in the back of the car. When I was reassembling, I was expecting to have only three of the four pulley bolts, but I had all of the bolts but didn't have the 30mm crank nut. My father distinctly remembered using the 30mm nut to rotate the engine and said that he never took it off because he removed the lower belt shield. So that's all still a mystery to me. My best guess is that it's in the floor drain at the mechanics garage.

I locked the cams again and removed the timing bolt and the crank serpentine pulley. I could feel ZERO rotational play on the crank. I didn't pull the timing pulley off because it was obvious that it was going to be a PITA to get it off the crank shaft. Certainly some rust and grime on the outside of the splines, but I don't have any reason to believe that they are slipping.

wieselaj · Post by **wieselaj** » 25 Mar 2018, 13:19

I would like to revisit one question i asked in the original post... Is it possible for the crank to be off one full turn? It doesn't make sense to me, but I saw this in another post from someone with an S60 that jumped time...

viewtopic.php?f=9&t=84244&p=461892&hili ... lt#p461892

"Second. After re-timing and then having what seemed like no compression, another big mistake due to me again! Now that I think about it, I rolled the engine over ONE turn in the process. DUH!"

"You forgot it is a four stroke not a two stroke."

Pulling the cam cover again isn't a big deal, but it's a messy one. But if it makes any sense that the crank needs to be advance a turn, I will obviously give it a try.