johnny250 Posted July 21, 2009 Report Share Posted July 21, 2009 Disaster strikes with only days to the International..... the saga so far..... The left exhaust pipe has always been a bit sooty compared to the right, so I thought I would give the SU's a bit of a tune up, seemed to go fine and took the car out last night to test it. Even my wife remarked how much smoother the engine seemed, so after about 15 miles, I found a clear bit of road and tried it flat out....all went well until I throttled back, when it started to misfire. I limped back home and diagnosed cylinder number 5 U/S...... the spark plug was well choked up with carbon and gunk (it has always been the mucky one) so I fitted a new one and tried a short test drive..... no improvement. Checked the compression, Cylinder 5......NONE! Lifted the rocker cover to make sure the valves were going up and down OK....they are, tappet clearance OK too....... your theories please gents........ john Quote Link to post Share on other sites
Guest ntc Posted July 21, 2009 Report Share Posted July 21, 2009 Disaster strikes with only days to the International..... the saga so far..... The left exhaust pipe has always been a bit sooty compared to the right, so I thought I would give the SU's a bit of a tune up, seemed to go fine and took the car out last night to test it. Even my wife remarked how much smoother the engine seemed, so after about 15 miles, I found a clear bit of road and tried it flat out....all went well until I throttled back, when it started to misfire. I limped back home and diagnosed cylinder number 5 U/S...... the spark plug was well choked up with carbon and gunk (it has always been the mucky one) so I fitted a new one and tried a short test drive..... no improvement. Checked the compression, Cylinder 5......NONE! Lifted the rocker cover to make sure the valves were going up and down OK....they are, tappet clearance OK too....... your theories please gents........ john Hi John That is a bugger after the trip you have just had, anyway back to the problem remove both pushrods from number five and check again, if still no compression then it's the head off to find out more Quote Link to post Share on other sites
Alec Pringle Posted July 21, 2009 Report Share Posted July 21, 2009 On the overrun, throttling back, might suggest valve rather than piston. Damage to the valve, or seat, or spring, or less likely pushrod, or even a cam lobe. Alternatively it's a ring or even just possibly a holed piston. You could try filling number 5 with oil and see if it disappears quickly - if it does, then piston or ring is the probable culprit. Neil's suggestion will also help narrow it down. Cheers, Alec Quote Link to post Share on other sites
Guest ntc Posted July 21, 2009 Report Share Posted July 21, 2009 (edited) On the overrun, throttling back, might suggest valve rather than piston. Damage to the valve, or seat, or spring, or less likely pushrod, or even a cam lobe. Alternatively it's a ring or even just possibly a holed piston. You could try filling number 5 with oil and see if it disappears quickly - if it does, then piston or ring is the probable culprit. Neil's suggestion will also help narrow it down. Cheers, Alec Hi Alec Could also be an unleaded valve seat that has let go? Edited July 21, 2009 by ntc Quote Link to post Share on other sites
Alec Pringle Posted July 21, 2009 Report Share Posted July 21, 2009 Hi Neil, indeed so, hence my reference to valve seat - but from what I've been told, an unleaded seat getting mangled is pretty audible to the driver . . . . No first hand experience, though. Cheers, Alec Quote Link to post Share on other sites
Guest ntc Posted July 21, 2009 Report Share Posted July 21, 2009 (edited) Hi Neil, indeed so, hence my reference to valve seat - but from what I've been told, an unleaded seat getting mangled is pretty audible to the driver . . . . No first hand experience, though. Cheers, Alec Hi Alec My money is on the insert still there but spinning loose,if I remember correctly John had some sort of problem with number5 before he then changed the crankcase breathing setup? Edited July 21, 2009 by ntc Quote Link to post Share on other sites
Richard71 Posted July 21, 2009 Report Share Posted July 21, 2009 What has he done to the engine breather set-up that could have affected the cyl head so adversly? Concerned to hear this??? Richard. Quote Link to post Share on other sites
johnny250 Posted July 21, 2009 Author Report Share Posted July 21, 2009 Hi AlecMy money is on the insert still there but spinning loose,if I remember correctly John had some sort of problem with number5 before he then changed the crankcase breathing setup? well remembered Neil..... yes number 5 has always been sooty/mucky from new, but has always run OK (a testament to the Mondeo ignition, seeing the state of the plug last night) I put off retuning the carbs till now.....no sign of soot in the tailpipe....but it is a little blue now!....think i went a bit too far on the lean side now Just taken the bonnet off to clear the roof when on the ramps, then the ramps spun out and collapsed as I was half way up as I foolishly went up in reverse in my haste to get out of the rain....no bonnet and roof down no damage done thankfully....so off with the head in the morning? john Quote Link to post Share on other sites
88V8 Posted July 21, 2009 Report Share Posted July 21, 2009 ....the ramps spun out and collapsed as I was half way up I hate ramps. Had a set years ago threw them away for this very reason. If you've holed the piston will be bigtime smoke. Bad luck whatever. Hope you find a miraculous solution. Without the pushrods I think it would make the IWE on 5 cyls if you go gently, altho not very satisfying I grant you. Ivor Quote Link to post Share on other sites
Guest ntc Posted July 21, 2009 Report Share Posted July 21, 2009 Without the pushrods I think it would make the IWE on 5 cyls if you go gently, altho not very satisfying I grant you. Ivor Errrrrrr sorry Ivor but no it would sound like an Audi but it would not do it any good Quote Link to post Share on other sites
johnny250 Posted July 21, 2009 Author Report Share Posted July 21, 2009 (edited) Errrrrrr sorry Ivor but no it would sound like an Audi but it would not do it any good It's looking like it will look like an Audi too....... my V6/A6 that is, for the weekend....... I would have limped to see Marko if i had been a bit closer, I couldn't get the pushrods out without lifting the rocker shaft so slackened the tappets right off and put a good measure of 20/50 in the plughole to see if that briefly restored compression at all.....it didn't, so started the strip down, hoping that its top end, not piston. To be honest i'm quite enjoying the chance to work on it again....just not this week john Edited July 21, 2009 by johnny250 Quote Link to post Share on other sites
Andy Moltu Posted July 22, 2009 Report Share Posted July 22, 2009 Hi JohnThat is a bugger after the trip you have just had, anyway back to the problem remove both pushrods from number five and check again, if still no compression then it's the head off to find out more If you remove both push rods then no air will get in to be compressed - you'll only get a flicker (assuming no mechanical problem) if the piston was at the bottom of the stroke when you took out the push rods. To be honest it looks like a head off job to investigate - unless one of the rockers haze seized holding a valve open - but that's pretty unlikely - sounds like either a valve or valve seat has gone AWOL or a piston is shot. A head gasket failure could do this too but you'd anticipate overheating or hissing if venting to the oustide. If the gasket had gone between pistons you wouldn't get overheating but the compressions would be down on the 2 adjacent cylinders (usually 3 & 4) Quote Link to post Share on other sites
RobinTR6 Posted July 22, 2009 Report Share Posted July 22, 2009 It's looking like it will look like an Audi too....... my V6/A6 that is, for the weekend....... I would have limped to see Marko if i had been a bit closer, I couldn't get the pushrods out without lifting the rocker shaft so slackened the tappets right off and put a good measure of 20/50 in the plughole to see if that briefly restored compression at all.....it didn't, so started the strip down, hoping that its top end, not piston. To be honest i'm quite enjoying the chance to work on it again....just not this week john John, sorry to hear your woes, good luck wuith the fix and travel to the IWE. I was looking forward to admiring that clock of yours again.... Robin Quote Link to post Share on other sites
Guest ntc Posted July 22, 2009 Report Share Posted July 22, 2009 If you remove both push rods then no air will get in to be compressed - you'll only get a flicker (assuming no mechanical problem) if the piston was at the bottom of the stroke when you took out the push rods. If it is blowing out though the valve it would also draw it in and you would hear it Quote Link to post Share on other sites
johnny250 Posted July 22, 2009 Author Report Share Posted July 22, 2009 (edited) Heads off........No:5 exhaust valve has piece missing........ looks like a strange failure, notice the cut on the back of the valve, like an oxyacetylene torch Next question, do I need to replace the cylinder head /exhaust/inlet gaskets or are they usable again? best place to get a valve? quickly? Notice that the valve seating area doesn't look shiny like the inlet ....Normal? also notice the state (carbon) of number 5 compared to number 4 (same carburettor) thanks john Edited July 22, 2009 by johnny250 Quote Link to post Share on other sites
Guest ntc Posted July 22, 2009 Report Share Posted July 22, 2009 (edited) Heads off........No:5 exhaust valve has piece missing........ looks like a strange failure, notice the cut on the back of the valve, like an oxyacetylene torch Next question, do I need to replace the cylinder head /exhaust/inlet gaskets or are they usable again? best place to get a valve? quickly? Notice that the valve seating area doesn't look shiny like the inlet ....Normal? also notice the state (carbon) of number 5 compared to number 4 (same carburettor) thanks john Hi John 1.You need to replace all 2.Whoever did your head, if you can give me the exact size's I may have one that I will let you borrow till you find another 3 Yes Is the piston crown ok and the bore if so you may have been lucky and it has gone out though the exhaust Edited July 22, 2009 by ntc Quote Link to post Share on other sites
johnny250 Posted July 22, 2009 Author Report Share Posted July 22, 2009 Hi John1.You need to replace all 2.Whoever did your head, if you can give me the exact size's I may have one that I will let you borrow till you find another 3 Yes Is the piston crown ok and the bore if so you may have been lucky and it has gone out though the exhaust Thanks Neil, (2) but I don't want to strip it down again....what dimensions are needed to get a replacement ( the company that did the unleaded valves seats years ago are no longer trading) strangely, the No.5 piston crown was the cleanest of them all and OK.....all the others were well crusty with carbon considering the limited amount of miles since the rebuild. john Quote Link to post Share on other sites
Guest ntc Posted July 22, 2009 Report Share Posted July 22, 2009 (edited) Thanks Neil, (2) but I don't want to strip it down again....what dimensions are needed to get a replacement ( the company that did the unleaded valves seats years ago are no longer trading) strangely, the No.5 piston crown was the cleanest of them all and OK.....all the others were well crusty with carbon considering the limited amount of miles since the rebuild. john Hi John You missunderstand you won't need to strip it again I can get another valve if need be, the dimension across the valve face,and lenth of stem last post here is 4.30 away if you want the car for Malvern. The last point we will discuss via Pm;s later Edited July 22, 2009 by ntc Quote Link to post Share on other sites
RogerH Posted July 22, 2009 Report Share Posted July 22, 2009 Hi John, the strange oxyacetylene burn mark is probably caused by the combustion flame exiting the hole in the valve before the valve is open causing even higher flame temp. The failure (wedge bit missing) looks fairly typical. I had this on an A35 back in the 70's. Strangely it didn't really affect the performance. Roger Quote Link to post Share on other sites
Guest ntc Posted July 22, 2009 Report Share Posted July 22, 2009 Hi John, the strange oxyacetylene burn mark is probably caused by the combustion flame exiting the hole in the valve before the valve is open causing even higher flame temp. The failure (wedge bit missing) looks fairly typical. I had this on an A35 back in the 70's. Strangely it didn't really affect the performance. Roger Hi Roger If the pic tells the story the face edge of the valve is broken not burnt Quote Link to post Share on other sites
Mk1PI Posted July 23, 2009 Report Share Posted July 23, 2009 (edited) I have seen and done this sort of thing to exhaust valves at least 4 times over the last 20 years.. Generally it will be due to a piston in slight trouble causing oil burning.. generally manifests as slight plug fouling on that particular pot. Often a poorly seated or tensioned oil control ring or can be a broken ring. This leads to carbon build up on the valve which can form a hot spot under the "right" conditions leading to valves melting like an oxy torch has attacked it. See photo.... This condition is not helped by 1. Slightly tight clearance on exhaust valve. 2. Slightly lean mixture. 3. Poor quality valve spec. Stellite faced are best (I have used Datsun 1600 33mm valves turned down to fit) 4. Hard running , generally up a hill at ~3000-4000rpm with all of the above conditions in place. I can place all of my exhaust valve failures to climbing long, moderate inclines at speed with many of the above stated faults (diagnosed or otherwise) 1975 2500PI ... 1990 M5 ~80mph uphill number 5 exhaust... plug had continually fouled until this episode... replaced oil control rings on piston 5 (loss of tension) whilst fixing the head 1971 2500PI ... 1995 Brisbane - Toowoomba up the dividing range ~70 mph number 5 exhaust valve .. hot day + probably a lean condition + minor oil burning.. 32m PI valves are not stellite faced (continued to Western Australia on 5 pots) 1977 2500S ... 2004 Greenmount Hill Perth WA ~60mph number 4 exhaust valve (and a couple more in trouble) 1973 2500PI ... 2006 Greenmount Hill Perth WA ~55mph number 3 exhaust valve (broken ring on piston 3) All these resulted in an exhaust valve looking IDENTICAL to yours Also note that I never had 1 or 6 go although this may just be chance, they also run a bit cooler?? Edited July 23, 2009 by Mk1PI Quote Link to post Share on other sites
johnny250 Posted July 23, 2009 Author Report Share Posted July 23, 2009 Thanks for that Mk1PI.....! I'm glad?? that I'm not alone in tearing the head off occasionally. I was revving the nuts off when it went, so can't complain too much. As mentioned, No.5 has always been the problem cylinder, although I left some oil on top of the pistons overnight and it was still there in the morning....is that a good enough test for ring condition? john Quote Link to post Share on other sites
Davidw Posted July 23, 2009 Report Share Posted July 23, 2009 Hi John - thanks for the PM. Now I see why your not taking the TR. Bummer!!! In my ltd exp. I would say that if the oil sat on the pistons overnight, then there's not much wrong with the rings. Sorry for your difficulty! All the best David Quote Link to post Share on other sites
88V8 Posted July 23, 2009 Report Share Posted July 23, 2009 As mentioned, No.5 has always been the problem cylinder, although I left some oil on top of the pistons overnight and it was still there in the morning....is that a good enough test for ring condition? Not really: No pressure. No movement. Cold vs hot. And it's the top edge of the ring that prevents seepage downwards. What matters is the performance of the bottom edges in scraping oil off the cylinder walls. Cords specialise in oil control, do they make rings for the 6? http://www.cordsduaflex.com/ If I were you I'd be wanting the piston(s) out this winter. Perhaps 'wanting' isn't the right word... Ivor Quote Link to post Share on other sites
Mk1PI Posted July 23, 2009 Report Share Posted July 23, 2009 Number five pot is obviously not running quite the same as the others as your plugs show. It may just be the ring gaps all aligned or maybe a slight lack of tension on the oil control ring. It may be the inlet valve guide Piston ring check / swap can be done without lifting the engine, 'just' drop the sump with the engine in situ. Quote Link to post Share on other sites
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