 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Car Forum / Volkswagen / Water Cooled Volkswagen Cars / March 2009Broken valve, why?
This is a 1.9 SDI engine. It was running on 3 cyl.and produced a lot of smoke. I diagnosed a compression loss on cyl #4. Pulled the head and #4 piston was sitting lower than #1(?). Maybe a bad bearing shell or bend rod. Pulled the oil pan and indeed a bend rod. Replaced the rod. I then serviced and cleaned the head but one thing wasn't right. Almost all the hydr. valve lifters were damaged. Dents and cracks were the cam hits the lifter. What could cause this? Maybe they didn't subtract and the pistons hit the valves(?) but I found no traces on the piston. I replaced all the lifters and let them settle over night. Finished the work and started the engine and it was running very smooth, no smoke or vibrations. I could here the valve lifters knock but thats normal with new lifters. Let the engine warm up until suddenly a loud ticking noise and then bang!!. I couldn't rotate the crank by hand, arrgh. Checked the timing but it was spot on. Pulled the head again and #2 exhaust valve was broken in four pieces!! I examined all the parts but I can't find any explanation why the valve obvious stayed open hit the piston and broke. Could a high oil pressure cause the lifter to lift the valve? This diesel has only one valvespring /valve so there's not much oil pressure needed to lift it. SFC I have seen a 1.8 gas engine develop sooo much oil pressure that the lifters would keep the valves open and the compression would drop to '0'. So your theory might be valid here. I have seen crankshaft sprockets break off their keyways. Camshaft sprocket did not shift any? Tensioner fail enough to allow the timing to change?  Signaturelater, (One out of many daves) > This is a 1.9 SDI engine. It was running on 3 cyl.and produced a lot of > smoke. I diagnosed a compression loss on cyl #4. Pulled the head and #4 [quoted text clipped - 17 lines] > > SFC > I have seen crankshaft sprockets break off their keyways. > Camshaft sprocket did not shift any? > Tensioner fail enough to allow the timing to change? This one of the first things I checked and the timing was spot on. The pump and cam aligned perfectly with the crank. One thing is puzzling me, the valve stem broke just under the two keys so above the guide. The keys were still in place with a little piece of the stem. Maybe the spring bend and snapped of the top of the stem(?). Have to investigate further..... SFC www.tdiclub.com has lots of diesel nerds. Camshaft timing incorrect and piston banged valves causing lifters to be damaged? In the US lots of folks get tools from www.metalnerd.com I suspect there are tools availible where you live from some vendor. In the US I spent $300 in tools just to change a timing belt. On my ALH TDI I have to break the cam sprocket loose, lock the cam by the vacuum pump, lock the crankshaft and some other things to properly time it. I would suspect a SDI would have similar procedures. If yu try to get it running again I woudl have a mechanical oil pressure guage hooked up to monitor oil pressure. >This is a 1.9 SDI engine. It was running on 3 cyl.and produced a lot of >smoke. I diagnosed a compression loss on cyl #4. Pulled the head and #4 [quoted text clipped - 17 lines] > >SFC Camshaft timing incorrect > and piston banged valves causing lifters to be damaged? In the US lots Could be, maybe the previous mechanic didn't do a good alignment > of folks get tools from www.metalnerd.com I suspect there are tools > availible where you live from some vendor. In the US I spent $300 in > tools just to change a timing belt. On my ALH TDI I have to break the > cam sprocket loose, lock the cam by the vacuum pump, lock the > crankshaft and some other things to properly time it. I would suspect > a SDI would have similar procedures. Same with the sdi engine, pump is locked with a pin, cam is locked with a bar in a slot on the gearbox side and the crank is set on the TDC mark "O". > If yu try to get it running again I woudl have a mechanical oil > pressure guage hooked up to monitor oil pressure. There happened to be an oil connection on the head for this!! SFC Lost track here. Did the head get new cam, lifters, valves and guides? Was the deck height checked on every cylinder? Was the timing mark on the flywheel confirmed with dial indicator? Was cam belt tensioner replaced? > Camshaft timing incorrect >> and piston banged valves causing lifters to be damaged? In the US lots [quoted text clipped - 17 lines] > >SFC > Lost track here. Did the head get new cam, lifters, valves and guides? > Was the deck height checked on every cylinder? Was the timing mark on > the flywheel confirmed with dial indicator? Was cam belt tensioner > replaced? Same cam, was still okay! Replaced the lifters with some good used ones, valves and guides were well within spec. Deck height was checked for the right head gasket, #2 (same as the orig. one). Timing mark on the flywheel is at tdc as piston #1. New belt and tensioner was fitted. I think there was too little play between the lifter and cam. Maybe the lifter didn't subtract far enough and when the valve expanded things went wrong. In normal cases oil is slowly added into the high pressure chamber of the hydr. lifter until the play is almost zero. But if there's already little play then the oil can't flow back because of the check valve. I read that h.lifter should be placed upside down for this. So with the cam side on the table. This way oil can slowly drain out of the high pressure chamber. This could also explain why the valve stem broke just under the keys. SFC So what are you replacing now? The oil pump too right............ along with all things broken/damaged? BTW Are complete engines easy to find for this vehicle there? >> Lost track here. Did the head get new cam, lifters, valves and guides? >> Was the deck height checked on every cylinder? Was the timing mark on [quoted text clipped - 18 lines] > > SFC Well the head and piston have some little indents and scratches but no cracks. These diesel piston are very heavy and have a thick crown! So I think I can still use them. I'll replace of course the broken valve and all off the lifters. I'll also check if the pressure control valve inside the oil pump isn't stuck. I've a spare pump of a tdi engine which should work, have to check the part# with etka. There are many varieties on this engine in terms of inlet manifold etc. This one is a ASX with some strange plastic velocity stacks inside the inlet manifold. I guess the base of the engine is pretty much the same and it's not difficult to find one. So if I blow it up again then this will be the final solution. What do you think of the broken valve tip? I can't understand why it broke just under the keys. You can almost bend a valve stem 45deg before it snaps but this was a clean horizontal crack! SFC |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2009 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.