Valve clearance adjustment
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From: Jason James on 22 Apr 2010 14:47 "The Raven" <swilson150(a)yahoo.com.au> wrote in message news:4bd035b7$0$24251$afc38c87(a)news.optusnet.com.au... > "Noddy" <me(a)home.com> wrote in message > news:4bd0217a$0$903$c30e37c6(a)exi-reader.telstra.net... >> >> " Scotty" <scoter1(a)warmmail.com> wrote in message >> news:4bd002bc$0$6094$afc38c87(a)news.optusnet.com.au... >> >>> Blow by is through the rings or valve stem seals? >> >> Rings. >> >> If it was through the valve stem seals the engine would be in *very* >> serious trouble. >> > > If he's getting lots of smoke just on acceleration (for a few seconds) it > could be valve stem seals. Easiest way to test is drive at a steady speed, > back off the throttle (change down a gear perhaps), then hit the throttle > several seconds later. Lots of smoke on throttle application indicates bad > valve stem seals (and or valve stem to head clearance).... oil is being > pulled from down into the intake ports from the top side of the head. > > Had this on a old Mazda 929. Aye,..what was it exactly about those early Mazdas? A neighbour had a 2 litre 6 cyl (929?) It used to lay a carpet of bluish/white smoke. One arvo, a copper followed him home. "I can see where have driven, over the last kilometre!!!" the Copper blasted him. Needless to say, that is where the Mazda lay,..until it was carted to the tip. Jason
From: Jason James on 22 Apr 2010 14:48 "The Raven" <swilson150(a)yahoo.com.au> wrote in message news:4bd035ec$0$7966$afc38c87(a)news.optusnet.com.au... > > "The Raven" <swilson150(a)yahoo.com.au> wrote in message > news:4bd035b7$0$24251$afc38c87(a)news.optusnet.com.au... >> "Noddy" <me(a)home.com> wrote in message >> news:4bd0217a$0$903$c30e37c6(a)exi-reader.telstra.net... >>> >>> " Scotty" <scoter1(a)warmmail.com> wrote in message >>> news:4bd002bc$0$6094$afc38c87(a)news.optusnet.com.au... >>> >>>> Blow by is through the rings or valve stem seals? >>> >>> Rings. >>> >>> If it was through the valve stem seals the engine would be in *very* >>> serious trouble. >>> >> >> If he's getting lots of smoke just on acceleration (for a few seconds) it >> could be valve stem seals. Easiest way to test is drive at a steady >> speed, back off the throttle (change down a gear perhaps), then hit the >> throttle several seconds later. Lots of smoke on throttle application >> indicates bad valve stem seals (and or valve stem to head clearance).... >> oil is being pulled from down into the intake ports from the top side of >> the head. >> >> Had this on a old Mazda 929. > "valve stem to head clearance" should be more correctly "valve stem to > guide clearance". It's late and I've had a few.... Reads like 4X?? :-) Jason,..narrr, it aint that bad....
From: John_H on 22 Apr 2010 17:34 Scotty wrote: >"John_H" <john4721(a)inbox.com> wrote in message news:ih20t51fndaeagc0om46rknckjn07q2okq(a)4ax.com... >: Scotty wrote: >: > >: >Blow by is through the rings or valve stem seals? >: >: Blow by is the combustion pressure (gas) that gets past the rings >: (unless there happens to be a hole in a piston). > >Excuse my ignorance but would it also come past the stem seals? No, because the valve stems aren't subjected to the forces of combustion, or compression. The stem seals are only there to prevent oil escaping past the valve stems and through the valve guides, the valves themselves provide the seal between the combustion chamber and the valve stems. In the case of the inlet valves, oil that gets past the valve guides would be sucked into the combustion chamber during the intake stroke and burnt in the combustion process. Oil that gets past the exhaust valve guides is picked up by the spent combustion gases during the exhaust stroke and exits via the exhaust. In short, faulty valve stem seals can cause excessive oil consumption but not a loss of compression. >Thats why I commented on if you put oil down the bore and it still shitty compression that it may be >valve seals? The only point (and there's very little point IMHO) of addding oil to the cylinders as part of a compression test is to prevent loss of compression past the rings should it be significant. Remember that the pressure of combustion that causes blow by past the rings will be much higher than the compression pressure. Hence the presence of blow by is a much better indication of of rings not sealing properly than a compression test will ever be. >Tell me if Im wrong so I can learn a bit here.............. after all aint that why this NG is here. -- John H
From: bugalugs on 22 Apr 2010 18:01 On 22/04/2010 11:40 p.m., The Raven wrote: > "Noddy"<me(a)home.com> wrote in message > news:4bd0217a$0$903$c30e37c6(a)exi-reader.telstra.net... >> >> " Scotty"<scoter1(a)warmmail.com> wrote in message >> news:4bd002bc$0$6094$afc38c87(a)news.optusnet.com.au... >> >>> Blow by is through the rings or valve stem seals? >> >> Rings. >> >> If it was through the valve stem seals the engine would be in *very* >> serious trouble. >> > > If he's getting lots of smoke just on acceleration (for a few seconds) it > could be valve stem seals. Easiest way to test is drive at a steady speed, > back off the throttle (change down a gear perhaps), then hit the throttle > several seconds later. Lots of smoke on throttle application indicates bad > valve stem seals (and or valve stem to head clearance).... oil is being > pulled from down into the intake ports from the top side of the head. > > Had this on a old Mazda 929. > > Or oil is being pulled up passed worn rings.
From: The Raven on 22 Apr 2010 18:03
"John_H" <john4721(a)inbox.com> wrote in message news:ole1t5d7mcna8b4nig69oq3h5c8pehu96f(a)4ax.com... > Scotty wrote: >>"John_H" <john4721(a)inbox.com> wrote in message >>news:ih20t51fndaeagc0om46rknckjn07q2okq(a)4ax.com... >>: Scotty wrote: >>: > >>: >Blow by is through the rings or valve stem seals? >>: >>: Blow by is the combustion pressure (gas) that gets past the rings >>: (unless there happens to be a hole in a piston). >> >>Excuse my ignorance but would it also come past the stem seals? > > No, because the valve stems aren't subjected to the forces of > combustion, or compression. The stem seals are only there to prevent > oil escaping past the valve stems and through the valve guides, the > valves themselves provide the seal between the combustion chamber and > the valve stems. > > In the case of the inlet valves, oil that gets past the valve guides > would be sucked into the combustion chamber during the intake stroke > and burnt in the combustion process. Oil that gets past the exhaust > valve guides is picked up by the spent combustion gases during the > exhaust stroke and exits via the exhaust. > > In short, faulty valve stem seals can cause excessive oil consumption > but not a loss of compression. > >>Thats why I commented on if you put oil down the bore and it still shitty >>compression that it may be >>valve seals? > > The only point (and there's very little point IMHO) of addding oil to > the cylinders as part of a compression test is to prevent loss of > compression past the rings should it be significant. True. I believe it gives a good indication if the compression loss is ring related. A 'dry' compression test followed by a 'wet' compression test will show the rings to be bad if the figures differ significantly. If the figures remain about the same it indicates a possible head problem (gasket, valves etc). It's not a fool proof method but it helps diagnose. > > Remember that the pressure of combustion that causes blow by past the > rings will be much higher than the compression pressure. Hence the > presence of blow by is a much better indication of of rings not > sealing properly than a compression test will ever be. Bad rings will generally cause smoke all the time. It might vary but it'll always be there. Bad valve guides/stem seals generally require high manifold vacuum (to suck the oil down into the manifold/cylinder) which will show up on acceleration (more on acceleration, then tapering off). |