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V8 smoking on startup - valve stem oil seals?


FridgeFreezer

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Yes, just as I decide to spend out on new tyres & suspension & bushes for the RRC it decides it's going to play up in the engine department <_<

Basically it's giving a fairly significant and prolonged cloud of blue smoke on startup from cold, and seems a bit down on power esp. noticable when towing. I think the two could well be unrelated as the engine is an unknown quantity but looks like someone has done some work as the block & heads are different colours to each other. It's not blowing out of the oil filler and the temp gauge is normal, in fact usually quite cool unless it's working hard.

It's never liked idling properly but I put that down to carp ignition system and Lucas EFi more than anyting :rolleyes:

I'm suspecting valve stem oil seals - am I on the right track, and if so how critical is it to get done / how hard to do?

Before any smart-arse diesel owner says "fit a TDi", when I searched for "smoke on startup" I got 20 pages of posts about rough running TDi's :P

Anyone still determined to mention diesel will be dressed as a hob-nob and thrown to Jez :ph34r:

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You're not funny, you know that <_<

I work with Guy the hob-nob line will be used in the project meeting next week. :lol:

Joking aside my 90 smoked on start up when I put £10 of Diesel in it by mistake....

I have a loverly 3.9 efi sat in my garden that will solve that smoking problem..

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do a compression test, if the figures read right then its probably the stem seals, if it doesn't then u might have cracked your ring :blink:

I can't believe Andy's not turned up yet with all this talk of Latex and broken rings :ph34r:

John, has this come in recently? If so, I'd have to go with M's theory about the rings.

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It occasionally smoked a teensy bit on startup for quite a while, but over the last half-dozen starts it's gone from a small puff to a rather noticable cloud, and blows a bit for the first minute or two of driving when you put your foot down.

Jules - it's a very nice 3.9, believe me it's very tempting about now too :rolleyes: but unless the price is right I might have to just get the spanners out on this one as all my dosh is going into the 109 at the moment.

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I'm here - just been off to the chemist for essential supplies :0

Hopefully the potions will be able to steam off a particularly troublesome piece of latex clothing. Its been a few weeks.

If its terminal - post up on WBBSC - I may be able to help you out.

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Its difficult to diagnose from a distance………… generally the V8’s don’t seem to suffer very much from stem seals/worn guides …….. probably because the to end isn’t exactly flooded with oil ……… :rolleyes:

The way forward is to do a cold dry compression test and follow that with a cold oiled compression test……………. for good measure do it all again when the engine is hot. Then post up the results so we can all laugh offer advise.

The cold figures will probably tell you all you need to know. :(

Also check all the breathers for splits / blockages ……….. and have a nosey in the oil separator flame trap. The other place to look is the breather inlet on the rear of the left hand bank (1 to 7) rocker cover……. this has a tiny hole that gets blocked with carp….. if that happens the tick over is not good and oil is sucked up past the rings. ;)

Ian

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Syptoms of worn stem seals/guides is a puff of smoke when you 'blip' the throttle.

Worn/broken rings are usually identified by continual smoke or at certain revs.

Oil in the rocker cover can seep down a worn valve guide overnight - hence the smoke being worse for a short period after starting it from cold. Doesn't usually manifest itself on all cylinders at the same time though. In the morning, disconnect the coil lead, spin the engine, then remove the plugs and see which ones are oily.

Dry compression test will identify a faulty cylinder.

Wet test will tell you if it's rings or valve.

Les. :)

P.S. Fit a diesel - they smoke ALL the time! :D

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Oil and filter were done recently (~3k), Bosch filter and Castrol GTX (15/40) didn't flush it but can't imagine that would cause it to do a TDi impression at startup? :ph34r:

Letting it cool down now for compression test later tonight, deep joy.

John,

IMVHO oil is too thin and 20/50 may buy you some time re thinness causing smoking.

Flushing the oil system can unstick sticky glued up rings and clean out passages (oooer we are off again) worth a try IMHO ?

Nige

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it is interesting what BBC says about v8 not suffering from this.

IIRC early oil seals were fibre ring type things that would break up and block oil ways so were of no use what so ever - only fitted to inlet valve; - the later ones are plastic upside buckets with a spring to hold them in place so the valve guide is stepped.

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Yes that is good stuff ………… but hardly copyright to puma engines ……… it is the stuff that every engine builder / tuner knows as part of his religion……………... :rolleyes:

Compression ration is usually defined as………. the piston displacement plus clearance volume, divided by the clearance volume. This is the nominal compression ratio of the perfect engine determined by the cylinder geometry alone. In practice, the actual compression ratio is appreciably less than the ‘perfect’ value because the volumetric efficiency of engine is less than 100%. This is mostly affected because of late intake valve closing and valve overlap. The above assumes a naturally aspirated engine.

The good part is the reference to the charge / air in the pipe to the measuting instrument ……….. often this is overlooked. The golden rules were always…….. avoid gauges with long pipes ………on the old standard ‘Snap-on’ gauge this used to be a (IIRC) 14inch hose ………. That equates to about 3cc volume and therefore the compression will read lower ……… because you have increased the displacement clearance ……….. so that gauge would read 20 – 25psi low.

To be fair cold compression dry/wet readings plus running vacuum readings will tell you all you need to know in terms on mechanical diagnostics. ;)

Now get out there and do the measurements ............. :P

Ian

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Interesting comments about the tester pipe length Ian. My tester stores the compression after the pipe, and once I've taken a reading, I then release the pressure. If the engine is cranked several times, then the 20-25psi inaccuracy is negated isn't it?, or at least greatly reduced, dependant on No, of compressions used in a single reading.

Les. :)

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Les,

Yes………….. because all the newer gauges have the Schrader valve at the end of the pipe closest to the cylinder head……….. so cranking will produce a very accurate result.

Some of the older gauges (and cheapo stuff) have the valve at the gauge head ……….. this is where the inaccuracy comes in……….. the old snap-on was like this …….. :rolleyes:

Ian

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In practice, the actual compression ratio is appreciably less than the ‘perfect’ value because the volumetric efficiency of engine is less than 100%. This is mostly affected because of late intake valve closing and valve overlap. The above assumes a naturally aspirated engine.

that isn't quite true. the valve timing can be designed even on normally aspirate engines to get over 100 % but it is related to the engine rpm so will not be the same value across the rev range (variable valve timing is the futrue).

bact to compression test; I am not sure the absolute value is that important providing it is not stupidly low, more important is that the readings match across the cylinders.

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