abbot Posted May 8, 2015 Share Posted May 8, 2015 Hi all, just been out for a blat and when making my way back I got caught up in slow traffic and noticed that there was smoke coming out of the bonnet vents.On closer inspection it seemes to be coming out of the rocker cover cap. When I removed the cap it seemed clean but there was quite a bit of smoke coming out of rocker cover. Any ideas what could be the root cause? Link to comment Share on other sites More sharing options...
elie boone Posted May 8, 2015 Share Posted May 8, 2015 Do you have a vent on the end of the rocker cover that goes into a catch tank ? or is the rocker cover cap the only breather for the engine ? Link to comment Share on other sites More sharing options...
abbot Posted May 8, 2015 Author Share Posted May 8, 2015 There is a vent pipe and catch tank. Did not think about checking that Link to comment Share on other sites More sharing options...
DaveMorris Posted May 8, 2015 Share Posted May 8, 2015 OUt of interest - what crossflow engine spec is this, what type of piston, how many miles since any sort of refreshj etc etc .. .. There are a small number of reasons for this type of venting. D Link to comment Share on other sites More sharing options...
Roger King Posted May 8, 2015 Share Posted May 8, 2015 If it's a standard Supersprint and you've more than 15,000 miles under your wheels it may well be the usual problem of the rings giving up the ghost.This is a very common problem, but you can't really expect a piston designed for a 50bhp 1300ccm motor to last long in a 120bhp 1700 with a much higher compression ratio and rev limit.But yes, do as suggested and make sure the breathers are clear. You should have one on the block (ideally fed up to the rocker cover) and one on the rocker cover (ideally a hose at the rear of the rocker cover leading to a catch tank). Later Supersprints omitted the one on the block and insanely relied solely on the filler cap as a breather! Link to comment Share on other sites More sharing options...
abbot Posted May 9, 2015 Author Share Posted May 9, 2015 My beast is a standard 1700ss which as far as I know has not had any refresh work. Just the annual oil change done by me. She has done 35k Miles.The car is not so old so as was describred there is a vent from the RH rear of the block that feeds to a catch tank with a second pipe comimg out of that and leading to under the car.This afternoon I emptied the tank, removed the pipes and ensured they were clear. After putting it all back together the immediate problem of smoke coming out of the bonnet vents seems to have abaited.So now the big question is, what do I need to do to refresh the engine t ensure that she does not give up on me on day.If it is just a head off, decoke, and new rings is that acievable by dropping the sump or is it an engine out job? Link to comment Share on other sites More sharing options...
elie boone Posted May 9, 2015 Share Posted May 9, 2015 a compression test when hot will give you some idea in what condition your engine is. Link to comment Share on other sites More sharing options...
abbot Posted May 9, 2015 Author Share Posted May 9, 2015 what sort of pressure value would be the borderline level? Link to comment Share on other sites More sharing options...
DaveMorris Posted May 9, 2015 Share Posted May 9, 2015 Start off by doing a pressure check on all 4 cylinders. They should all come out at relatively the same value. Don't worry (initially) too much about the absolute values - post them up and let an expert like Roger make comment. (Don't forget - do the compression test with throttle fully open),Dave Link to comment Share on other sites More sharing options...
abbot Posted May 10, 2015 Author Share Posted May 10, 2015 As suggested I have done a compression test.engine hotthrottle wide openNo1 13No2 12No3 11.5No4 12So what do we make of that? Link to comment Share on other sites More sharing options...
Roger King Posted May 10, 2015 Share Posted May 10, 2015 Bar?If so, they're reasonably even and reasonably healthy. I can't give any details specific to your engine, but sometimes a failing oil ring lets oil through to the compression rings and artificially "seals" them, giving a false good reading.I can only state that at 35,000 miles a large percentage of Supersprints would have ring problems. I would suggest you keep running the engine and see if the problem returns. If it doesn't - great, but if it does, the only real way to pressurize the crankcase is through failed rings or broken pistons. Link to comment Share on other sites More sharing options...
abbot Posted May 11, 2015 Author Share Posted May 11, 2015 Thanks for your feedback Roger.yes it is BARi will continue to run it and keep a close eye on her.If i was to set about doing a refresh, can the rings be changed by dropping the sump? Or is it engine out job Link to comment Share on other sites More sharing options...
Area Representative dikko Posted May 11, 2015 Area Representative Share Posted May 11, 2015 You can 'top & tail' it without taking the whole engine out. Head and sump off, undo big end bolts and tap each piston out. Replace rings and put better end bolts back. Roger may recommend a quick glaze-bust with a strange looking tough mop thing attached to a drill if the bores look too shiny.Good wash out and it'll be like new.Nobody has mentioned valve-stem wear - might this not be a breathing cause?New fuel pump too (not a cheap one) might not be a bad idea. A lot of piston cooling etc depends on reliable delivery - as I've just found out... Link to comment Share on other sites More sharing options...
Roger King Posted May 11, 2015 Share Posted May 11, 2015 You should take Dikko's advice. He's had a 7 longer than most people have been walking on this planet!The tough mop thing he is referring to is a Flex Hone. This will put a new finish on the bore which is essential when fitting new rings. You do, of course, have to be sure that the bores have no significant wear before you go ahead. And I would fit new pistons rather than just rings; the pistons are notorious for failing as well.In an ideal world, you'd swap the pistons to forgings. This would mean a complete strip down and small rebore though.Regarding valve wear. The Supersprint is known for wear in this area, largely because Caterham went to the trouble of fitting decent valves, but left the standard guides in place which are not really compatible with the valve material. I think it unlikely that this would be severe enough to cause your breathing, but if the head is off anyway, have a look. If you have wear problems, the guides can be lined with a bronze sleeve which will solve the problem completely. Link to comment Share on other sites More sharing options...
abbot Posted May 11, 2015 Author Share Posted May 11, 2015 Dikko, did you mean New Oil Pump? Not sure how Fuel pump aids cooling Link to comment Share on other sites More sharing options...
Richard K Posted May 11, 2015 Share Posted May 11, 2015 What Dikko means is that if your fuel pump is not deliviering enough fuel it can lead to localised heat issues 'running lean' and piston melt down.Richard Link to comment Share on other sites More sharing options...
abbot Posted May 11, 2015 Author Share Posted May 11, 2015 Thanks Richard,That is a bit of theory that is way above my payscale. Link to comment Share on other sites More sharing options...
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