PeteStupps Posted December 26, 2019 Share Posted December 26, 2019 Merry Christmas all, Just on my way back to London from the ancestral home in my 1300fwd, with 1800 troublesome miles since I rebuilt the engine. Before leaving I reset the valve clearances, which were all slightly slack (because it's colder than when I last did them?), and I had a slightly worrying rumble at about 1800 rpm. Assumed that was something resonating cos it was loud inside the car but couldn't really hear anything leaning over the engine. Plugs all looked ok, though 1 and 4 were just a bit on the pale side. Then cruising along at about 60 suddenly lost power and a mad racket was coming from the engine. Pulled over and engine stopped, popped bonnet up, smoke was pouring out of air intake, which turned out to be from rocker cover breather. Whipped plugs out, no.4 was very stiff and when I got at out it looked like pic below. Oh dear. Looking through plug hole I could see exhaust valve was battered, and then disaster; massive hole in the piston. Any suggestions as to why this has happened?? I've never holed a piston before. Link to comment Share on other sites More sharing options...
yorkshire_spam Posted December 26, 2019 Share Posted December 26, 2019 (edited) Has it dropped valve or are all the stems/collets still in place? My Spitfire 1500 did this to us back in 2015... No hole in the piston top, but it smashed the valve guide out of the head and broke the end off the rocker before squashing the valve and wrecking the end of the plug (similar to yours) Good luck! Sam Edited December 26, 2019 by yorkshire_spam Link to comment Share on other sites More sharing options...
PeteStupps Posted December 26, 2019 Author Share Posted December 26, 2019 Thanks! Valves are all still apparently where they should be, so not sure what's happened. I can just see the inlet valve head through the spark plug hole but not exhaust. Not sure if I should be able to see either of them. Turned crank over and rockers and valves are all moving as you'd expect. I am wondering if the rumble at low revs was any sort of clue, but can't think what. Oil pressure was very high, over 75 while cruising. Had only done 15 miles so oil wasn't hot. Wonder if exhaust valve seat dropped off and broke up or something? It'll be a while before I can take head off and investigate. Link to comment Share on other sites More sharing options...
PeteStupps Posted December 26, 2019 Author Share Posted December 26, 2019 Smashing the valve guide out is quite impressive! Link to comment Share on other sites More sharing options...
RedRooster Posted December 26, 2019 Share Posted December 26, 2019 Thought i did i good job of wrecking the GT6, new block, crank, pistons, etc.... but it never did that. Doesn't look like a holed piston more like piston to valve contact, suggest the chain has slipped. RR RR Link to comment Share on other sites More sharing options...
PeteStupps Posted December 26, 2019 Author Share Posted December 26, 2019 It's not an interference engine though is it?? It's bog standard deck and head height. Slight update: there's no gap at all between cylinder 4 exhaust valve and the rocker. Suggesting valve head or seat is not in same position as it was 15 miles earlier. Inlet on same cylinder is normal, ten thou gap. I can see a massive hole in the piston crown, can't get decent photo of it through the spark plug hole though. Link to comment Share on other sites More sharing options...
GT6Steve Posted December 26, 2019 Share Posted December 26, 2019 What kind of valve guide material was it? I wonder if the first one stuck and then parts bent the second valve? Link to comment Share on other sites More sharing options...
thebrookster Posted December 26, 2019 Share Posted December 26, 2019 Did you have new valve seats installed when you rebuilt the engine? Phil Link to comment Share on other sites More sharing options...
Nick Jones Posted December 26, 2019 Share Posted December 26, 2019 Ouch! Not good...... Sounds like it’s dropped the exhaust valve or seat seat - unless there’s a stray something gone down the intake........ You can maybe check by backing off the adjuster on no.4 exhaust and seeing whether the valve follows it up. Somewhat academic now...... Did you limp it home with no 4 plug disconnected? Link to comment Share on other sites More sharing options...
PeteStupps Posted December 26, 2019 Author Share Posted December 26, 2019 45 minutes ago, thebrookster said: Did you have new valve seats installed when you rebuilt the engine? Phil Yes indeed, hardened exhausts. I am wondering if that is the culprit, especially as I was going to get same bloke to do my Spitfire head. Nick - no I didn't fancy 130 miles down the A1 like that, plus she wouldn't start when I tried anyway. I called the AA and waited in the pub. Halfway back now. Link to comment Share on other sites More sharing options...
Nick Jones Posted December 26, 2019 Share Posted December 26, 2019 If it is a dropped seat then I reckon your man owes you an engine Link to comment Share on other sites More sharing options...
PeteStupps Posted December 26, 2019 Author Share Posted December 26, 2019 12 minutes ago, Nick Jones said: You can maybe check by backing off the adjuster on no.4 exhaust and seeing whether the valve follows it up. Somewhat academic now...... I thought about doing that, but it was raining so decided it could wait! I'll be looking after the kids for a few days now so proper investigation will have to wait. Having had some time to think about it I'm a bit depressed now. Initially it was an interesting short-term inconvenience but now the prospect of fixing it has sunk in. This was my only road-worthy car. Bah humbug Link to comment Share on other sites More sharing options...
PeteStupps Posted December 26, 2019 Author Share Posted December 26, 2019 3 minutes ago, Nick Jones said: If it is a dropped seat then I reckon your man owes you an engine If that is the cause i'll certainly be discussing it with him! Link to comment Share on other sites More sharing options...
PeterC Posted December 26, 2019 Share Posted December 26, 2019 Plug earth strap detached> very retarded spark >preignition> piston crown under ev melts. Just guessing Peter Link to comment Share on other sites More sharing options...
Nick Jones Posted December 26, 2019 Share Posted December 26, 2019 Just now, PeterC said: Plug earth strap detached> very retarded spark >preignition> piston crown under ev melts. Just guessing Peter Not with mechanical damage like that to the plug.......... Only roadworthy car....... not any more No dropping of the sump for a quick piston swap on a 1300 FWD......... Link to comment Share on other sites More sharing options...
PeterC Posted December 26, 2019 Share Posted December 26, 2019 Nick, Its molten aluminium from the piston crown that has stuck to plug. Possibly the earth strap failed at the bend and embedded in the crown and made a hotspot that triggered preignition. Peter Link to comment Share on other sites More sharing options...
yorkshire_spam Posted December 27, 2019 Share Posted December 27, 2019 Sadly my money is on a dropped exhaust valve seat :-( Link to comment Share on other sites More sharing options...
PeteStupps Posted December 27, 2019 Author Share Posted December 27, 2019 Maybe not totally conclusive but I slackened off the rocker and removed pushrod. The suspect exhaust valve rises up about an inch higher than its neighbours, so either the valve head has shrunk or the seat insert has made a break for freedom. Link to comment Share on other sites More sharing options...
yorkshire_spam Posted December 27, 2019 Share Posted December 27, 2019 Yep, sad to say either Mr Valve or Mr Seat are really unhappy in there. Link to comment Share on other sites More sharing options...
Nick Jones Posted December 27, 2019 Share Posted December 27, 2019 Seems like quite a big gap for a simple missing seat...... but I suppose that the valve head is likely to be distressed as well...... interesting the the push-on cap stayed in place - collets often let go in similar circumstances, adding to the mayhem. Curious to see how things look with the head off....... Have some small-crank parts (Head,block, rods etc) here if needed. Link to comment Share on other sites More sharing options...
PeteStupps Posted December 27, 2019 Author Share Posted December 27, 2019 Thanks Nick, I'll post some pics as and when I get the head off (won't be for a few days) and we'll see what the damage is. If the block is scrap then I'll probably put a dust sheet over the car and ignore it for a year or two! I wondered why they used those push-on valve caps on these instead of the collet type. These are a lot easier to assemble. It's only got the standard soft springs, which probably helped keep things together. Link to comment Share on other sites More sharing options...
PeteStupps Posted January 1, 2020 Author Share Posted January 1, 2020 I have an update on this sad tale, after getting a few cold hours in the garage. Got the head off, and there is most definitely a hole in the piston! Exhaust valve seat is still securely in position, well battered though. The exhaust valve itself is not entirely present and correct. Looks like the valve head separated from the stem... I've heard of this happening but not seen it before. Is it likely to be anything other than a manufacturing flaw? Here's some pics of the piston and bore: Link to comment Share on other sites More sharing options...
PeteStupps Posted January 1, 2020 Author Share Posted January 1, 2020 Now some photos of the head. I presume this amount of damage to the combustion chamber means it's scrap... I have a spare 1500 head which doesn't require much work except new valves. The question is where to buy valves that don't fall apart. Link to comment Share on other sites More sharing options...
PeteStupps Posted January 1, 2020 Author Share Posted January 1, 2020 (edited) .. and now some pictures of the offending valve, or what's left of it. I don't know if it's possible to tell what caused the failure - presumably not, as the broken end will have been peppered by debris after it broke. I did a side-by-side comparison with an old exhaust valve from the same engine, then against a new inlet valve just to see if it broke somewhere obvious. The old valve is too coked up to see but against the new one you can see the break lines up with the weld (?) line. Are the stem and head welded together? Lastly here is a close-up of the stem end where it broke. Edited January 1, 2020 by PeteStupps Edit: one of the images Link to comment Share on other sites More sharing options...
Nick Jones Posted January 1, 2020 Share Posted January 1, 2020 Ouch...... The piston is clearly very dead. The valve likewise. That's a very clean break on the stem...... presumably showing that the head was welded to the stem and has separated. Pretty clearly a manufacturing defect IMO and I'd worry about the other three...... The head might actually go again. It's ugly, but provided the basic shape remains, and any sharp edges that might glow and cause pre-ignition are dressed out, no reason why it shouldn't function. The only part that gives me pause is the seat insert....... something to discuss with your man perhaps? Your 1500 head would need a very big skim to get the CR up on a 1300. I have a 13/60 head here but it's very well used...... Nick Link to comment Share on other sites More sharing options...
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