Tipidave Posted January 20, 2019 Report Share Posted January 20, 2019 The problem was poor starting, rough running and top end noise. Low pressure in all four cylinders but esp lie in two and three (55-60 psi) which didn't improve when retested with oil in the bore. Having removed the head from my herald 1200, a chipped no 3 exhaust valve was obvious... but what else? Number 4 piston has an area devoid of any carbon and looks a bit pitted... almost as if it is striking the head... but no corresponding mark on the head... should I be concerned? If I get yhebhraf skimmed this could be a problem? What else might cause this pattern? Also is the orange brown deposit deposit on the exhaust valves normal or indicative if some fault? The cylinder bores look pretty clean just a slight lip and minimal scoring or play evident... so I just plan to clean the crowns (which to my eye don't look too badly coked) leaving a small ring around the edge... is this the right approach? What else can I look for that might help to understand the story? Any advice greatfully received.? Link to comment Share on other sites More sharing options...
Pete Lewis Posted January 20, 2019 Report Share Posted January 20, 2019 thats a pretty normal valve burn , starts with a seating and forms a cracked looking burn out , the deposit is often down to the fuel used UL and addatives can leave coloured deposits , not to worry. leave a ring around the piston perifery i reckon is a bit old hat some care with a scraper , load some thick oil and wind the piston up and down wipe out the deposits left in the oil works well. the clean area is probably down to fuel washing , has it been richened up to compensate poor compression . like a rich idle mix on a downdraft carb ?? pete Link to comment Share on other sites More sharing options...
Tipidave Posted January 20, 2019 Author Report Share Posted January 20, 2019 Not rich I think. The engine did overheat quite badly due to a coolent leak. One of the head but washers was dished... I will go back to check if that was on number 4. I am concerned the the piston crown is percussing the head hence the clean area on number 4 and that the gudgeon is worn and allowing the piston to. Make contact with the head. Is this possible? Link to comment Share on other sites More sharing options...
Pete Lewis Posted January 20, 2019 Report Share Posted January 20, 2019 i guess its likely but not normal has it been consuming coolant being another good cleaner if the gaskets been seeping Pete Link to comment Share on other sites More sharing options...
Tipidave Posted January 20, 2019 Author Report Share Posted January 20, 2019 Possible but I haven't driven it enough to know. It was laid up in a garage and stored for nine years... I'm wondering now if this is why it was taken off the road in the first place... just seems odd to me that only the small crescent area is clean metal... that said there is no corresponding evidence on the face of the head. I have check and all washers under head bolts flat except for the one between 3 and 4 on the manifold side which is definitely dished. I would like to diagnose what has happened before proceeding with the head! 😀👍 Link to comment Share on other sites More sharing options...
Pete Lewis Posted January 20, 2019 Report Share Posted January 20, 2019 dished washers is a triumph failing , its normal, and not desired always used hardend HD and Nuts ex canley classics and others pete Link to comment Share on other sites More sharing options...
NonMember Posted January 20, 2019 Report Share Posted January 20, 2019 A clean area on one side of a piston can sometimes be caused by a head gasket leak allowing (a small amount of) coolant into the combustion chamber. Which I see Pete has already said, but that was my first thought on seeing the picture. Link to comment Share on other sites More sharing options...
JohnD Posted January 20, 2019 Report Share Posted January 20, 2019 4 hours ago, Tipidave said: The problem was poor starting, rough running and top end noise. Low pressure in all four cylinders but esp lie in two and three (55-60 psi) which didn't improve when retested with oil in the bore. The damage to the valve explains the low compression on 3, but if No.2 was as bad then suspect the valve(s) there too. Probably exhaust as those take the beating. The oil test not cincreasing Compression is diagnostic of a valve problem. You will need a new No.3 exhaust valve, and all the others need evaluation of the valve guides and grinding in. This will remove any 'lead memory' so with the head off, now is the time to have steel exhaust valve seats inserted. to remove any fear of recession. New valve guides will need the seats to be recut anyway, so steel seats definitely for any so treated. John Link to comment Share on other sites More sharing options...
Nick Jones Posted January 20, 2019 Report Share Posted January 20, 2019 The witness mark on no4 could be steam cleaning due to head gasket leak or might be a squish shadow due to some wear in big-end bearing allowing the piston to make a closer approach to the head than usual. Would have thought you might be able to hear that much wear though. Not too bad a job to drop the sump to check the bearings if so inclined, though a wipe-clean head is an advantage! Nick Link to comment Share on other sites More sharing options...
Tipidave Posted January 20, 2019 Author Report Share Posted January 20, 2019 Thanks for all the advice! I will take head to a local company for a pressure test and skim and ask about the other work. I am still a bit perplexed by the clean area in the no 4 cylinder head. If you look carefully it is looking a bit marked as if perhaps it is hitting the head... there is no corresponding evidence on the head itself so maybe I am over analysing it a bit. Just want it to be right!!!! 😀😀👍 Link to comment Share on other sites More sharing options...
Tipidave Posted January 20, 2019 Author Report Share Posted January 20, 2019 The other thing is that it did sound wrong .... a bit percussive and noisy as if I had a blowing exhaust. Link to comment Share on other sites More sharing options...
NonMember Posted January 20, 2019 Report Share Posted January 20, 2019 4 minutes ago, Tipidave said: The other thing is that it did sound wrong .... a bit percussive and noisy as if I had a blowing exhaust. The cracked valve on No 3 could well explain that. Link to comment Share on other sites More sharing options...
johny Posted January 20, 2019 Report Share Posted January 20, 2019 8 minutes ago, Tipidave said: Thanks for all the advice! I will take head to a local company for a pressure test and skim and ask about the other work. I am still a bit perplexed by the clean area in the no 4 cylinder head. If you look carefully it is looking a bit marked as if perhaps it is hitting the head... there is no corresponding evidence on the head itself so maybe I am over analysing it a bit. Just want it to be right!!!! 😀😀👍 How much of a skim will you ask for? Maybe a little extra to increase the compression ratio..... Link to comment Share on other sites More sharing options...
Tipidave Posted January 20, 2019 Author Report Share Posted January 20, 2019 I think I will take advice from the engineers.... they weee recommended by a garage that I use for MOT and other work. It is many years since I did any of this... I have some experience but when you see something unexpected I like to understand before jumping in... it is a bit like a detective story. I am sure all of the signs are there it is a case of interpreting it! Thanks for all the advice Great stuff👍👍 Link to comment Share on other sites More sharing options...
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