Except you were suggesting using a screwdriver or drift. Not knowing how adept the OP is, the tap on the rocker arm delivers the impact where it is needed and not on the valve cap (collar) or collets, which would not necessarily move the valve stem. As I am sure you will agree.Post #8 seems relevant.
Richard
The valve stem guide will not be dislodged by tapping the valve stem downwards. I'm guessing that the GM10 is an interference design so damage might be a possibility. However, there is nothing to lose by proceeding as suggested in post #8.
Brings back (un)happy memories. Little tinkle from the engine one evening leaving work - sounded just like pinking. Nothing obvious wrong with top end (only about 3000 miles into a brand new unleaded head). Head off, still nothing, perfect bores. So out it came one Christmas/New Year. broken ring was on the last piston that came out.Then his problems are just beginning. I always try the least invasive and most likely solution first. It it is just a stuck valve, it may free. If not ... onward Horation.
I just, in search of a light clacking noise in my MG engine, ended up replacing a piston and conrod. Not absolutely essential, but once you know it's there.... I enjoyed the work.
Errrr .... the mallet is used to knock the valve stem which stands proud of the collets so you won't be hitting those. If the valve gear has not been removed, as I specifically referred to, then you will obviously need to tap the rocker as there is no other way to tap the valve stem. The screwdriver is for levering the valve up if you do get a bit of downward movement. Hence my use of the term "up and down with a little WD40".
OK, so maybe it's the inlet port rusted through.
Really depends on how hard it is hit and how much it has seized, agree a light tap may free it. Bear in mind that the engine has been turned on the start motor, if the valve is seized in the guide probability the piston has already smacked the valve head compounding the seizure or not. Would seriously suspect a bent pushrod.
I would expect the inlet port to be further away from water and to be cooler and therefore less likely to succumb to corrosion.
I am sure you are absolutely correct, as always. I am not in the slightest bit bored.Errrr .... the mallet is used to knock the valve stem which stands proud of the collets so you won't be hitting those. If the valve gear has not been removed, as I specifically referred to, then you will obviously need to tap the rocker as there is no other way to tap the valve stem. The screwdriver is for levering the valve up if you do get a bit of downward movement. Hence my use of the term "up and down with a little WD40".
I'm sure you will agree that this is the best way to proceed.
Richard
Tele-diagnosis is full of speculation, but I wouldn't get too hung up on a stuck inlet valve. The OP has been dosing the cylinder with oil, and normal valve events have the inlet opening before TDC. At low cranking rpm there's plenty of scope for oil in the cylinder to be blown through the inlet.
So he says excessive tappet clearance is apparent on the inlet valve, so we must reasonably speculate that we have a seized inlet valve or a possible bent push rod or indeed both. The valve overlap will only be a few degrees and the total lack of compression with the emission from the inlet tract should indicate a lack of seal.
I don't understand why this seems to be a common theme on this thread. Why not see if it's a sticking valve first as checking that is en route to head removal ..... if that is ultimately what is needed.
Because the original post states that oil has historically been needed to increase the compression to assist start. It is then a clue to underlying issues. The cause now may be indeed that a valve is sticky, or the pushrod is bent given that the post states excessive tappet clearance. My best guess that the underlying history suggests badly pitted seats or a ring/cylinder issue.I don't understand why this seems to be a common theme on this thread. Why not see if it's a sticking valve first as checking that is en route to head removal ..... if that is ultimately what is needed.
Richard
I suspect that the oil might be functioning as "easy start" to start the engine rather than sealing the bore but, either way, I would still check for a stuck valve before rushing to remove the head as it's part way through the same process.
I think you are refering to 'hydraulic lock'? This one does not sound like a bent rod, as virtually no compression. So likely a stuck valve in some way. If the rod was bent enough to give no compression, it would be banging the block. I had that with a new Vetus(Mitsubishi), Still had compression, but was 3mm down on TDC and touching the block.
