350 Mag Mpi hard to start when warm or hot

[alldodge]

No
To obtain zero lash hold the push rod with your fingers and feel for up/down slop. Loosen the nut until you feel some up/down movement, turning movement is not used. Once all up/down is gone, this is zero lash. Now turn the nut down one full turn, your done with that lifter

I use a grease pencil and mark nut once done. I also adjust any others that are next to another valve being opened. If valve is being opened then the other of same cylinder is closed

 

[Scott06]

Thanks for reply. I screw rocker nut down until no lash or play. But when I tighten 360 degrees as per manual it opens the valve. Is that correct?

Screen shots attached show how to do a static and running valve lash.
if done correctly when you go one turn past zero lash the valve should not be open assuming the cylinder is on rdc on compression stroke. If it opens likely yiu were past zero lash when yiu started the turn

 

[nigb]

No
To obtain zero lash hold the push rod with your fingers and feel for up/down slop. Loosen the nut until you feel some up/down movement, turning movement is not used. Once all up/down is gone, this is zero lash. Now turn the nut down one full turn, your done with that lifter

I use a grease pencil and mark nut once done. I also adjust any others that are next to another valve being opened. If valve is being opened then the other of same cylinder is closed

Ok thanks Alldodge I will try that again in morning & report back. I had the boat surveyed when I bought it & the compressions were all reported to be in 157 - 170 range.

 

[nigb]

Screen shots attached show how to do a static and running valve lash.
if done correctly when you go one turn past zero lash the valve should not be open assuming the cylinder is on rdc on compression stroke. If it opens likely yiu were past zero lash when yiu started the turn

Thanks that might be issue too. No tdc marker on front of engine & engine is so tight a fit I can't see down there anyway. Have been judging tdc by valve positions maybe I need to review that. Am I right in thinking that when valve is closed some oil drains out of lifter? On the no 1 valves for instance when I lift rocker away from valve I can feel spring pressure in the lifter as the push rod presses down on it. I couldn't feel that on no 7 it was solid

 

[alldodge]

There is a spring in the lifter. With valve closed and one turn past zero lash there should be no up/down movement

 

[nigb]

There is a spring in the lifter. With valve closed and one turn past zero lash there should be no up/down movement

If valve is closed with zero lash & before the 1 turn past zero lash there is no up/down movement is that a problem?

 

[alldodge]

If valve is closed with zero lash & before the 1 turn past zero lash there is no up/down movement is that a problem?

This is how it should be ... as you said before the one full turn

 

[nigb]

I don't think you guys realise I have a problem with a fully extended plunger. I can see the lifters & if it wasn't for the lifter guide I would be able to get them out without removing manifold as when I get a magnet on them the lifter body lifts up until it hits the lifter guide. If you look at photo on right the push rod seat on no 7 is hard up against retaining clip & won't compress at all which is why it is opening valve when I give it an extra turn after zero lash. The photo on left is no 1 which is fine & you can see push rod seat is down the bore away from clip & it compresses fine. I need to take manifold off to see why they are jammed unless someone has a better suggestion.

This is how it should be ... as you said before the one full turn

 

[alldodge]

which is why it is opening valve when I give it an extra turn after zero lash

If lift is all the way up then the cam lobe is under it and your adjusting wrong.

Do this to make sure the valve your adjusting is fully closed.
Start with any cylinder which has one of it's valves being opened. Adjust the other valve and mark when done.

Find another which one of the valves is opening and adjust the other.

When all of those are done, rotate crank until you can do more valves. Keep rotating until you have managed to adjust all

 

[nigb]

If lift is all the way up then the cam lobe is under it and your adjusting wrong.

Do this to make sure the valve your adjusting is fully closed.
Start with any cylinder which has one of it's valves being opened. Adjust the other valve and mark when done.

Find another which one of the valves is opening and adjust the other.

When all of those are done, rotate crank until you can do more valves. Keep rotating until you have managed to adjust all

I have definitely done it that way. For some reason the lifters on this cylinder suddenly developed this fault where the valves no longer closed properly - there was no human intervention that did this. There must be a fault with lifter for it to do that surely?

 

[nigb]

I have definitely done it that way. For some reason the lifters on this cylinder suddenly developed this fault where the valves no longer closed properly - there was no human intervention that did this. There must be a fault with lifter for it to do that surely?

Just to clarify the lifter is all the way down it is the plunger which is not retracting at all it is fully extended against the retaining clip

 

[alldodge]

Looks like need to remove it to inspect

 

[nigb]

Inlet & exhaust lifters stuck up against retaining clip. Soaked them overnight in a new WD40 super penetrating fluid & they fell apart. Cleaned & reassembled them & they are working fine & motor now starts when hot. One tappet was noisy but once engine was warm & an increase in revs it soon quietened down. Sea trial tomorrow.
In hindsight I should have done compression test which would have highlighted the dead cylinder but boat was going so well we didn't think it could only be running on 7 cylinders. Also the low vacuum reading of 12 in Hg pointed to a valve timing issue which in fact it was on one cylinder. I will report back sea trial tomorrow. I hope my findings help someone else with this hot start issue. I see so many posts on other forums where people don't post their solutions to a problem

 

[nigb]

Sea trial about 40 minutes boat performed perfectly straight on plane without trim tabs down, had to throttle right back to keep her steady at 22 knots. Even after a hard turn she slowed to 17 knots & picked up back to 22 knots without me touching the throttle. However although better she still doesn't always start easily when hot. Compression in the dead cylinder now good. Vacuum gauge 16" Hg at idle which according to mercruiser manual is good. I am going to fill tank & run some injector cleaner through see if that helps but in meantime i need to do some more troubleshooting.

 

[dubs283]

16in at idle is good, yes. Needs to be steady, like less than +/- 1in for minutes

If fuel pressure under load is okay with a vacuum drop continously until wot with steady you're good, for now

 

[nigb]

16in at idle is good, yes. Needs to be steady, like less than +/- 1in for minutes

If fuel pressure under load is okay with a vacuum drop continously until wot with steady you're good, for now

Thanks for that info. I will double check vac at idle for a longer time & wot vac too. Also same with fuel pump but that was brand new 2 years ago. Your last 2 words concern me 'for now'!