Mercruiser Alpha one 5.7 Valve adjustment

[ukstu]

I'd like some advice from you that know better if possible please.
I've had both heads off and am in the process of rebuilding. In the past, i have had problems setting the valves, no matter how i follow instructions etc.. I am under no illusion i am doing something wrong but can't figure out what.
(Bear with me as this is just from memory and i do follow the book when i do it but..) Once heads are fitted, i remove any lash on each push rod, then put each cylinder to TDC and as i understand it is then 1/2 or 3/4 turn to tighten rockers down.
When i do this, it is opening the valves slightly and causing me to have no compression at all on each cylinder.

Could someone please advise or give some advice? If this sounds wrong then it is my memory getting in the way, but, following the manual, the final 1/2 or 3/4 turn causes the issue.

Please help..

Thanks in advance.

 

[Lou C]

You may be going past the zero lash point. I did zero lash and 1 more turn on my '88 4.3 and had no problems doing it that way. To measure lash, back off the rocker arm retaining nut till there is play in the push rod, then tighten it while moving the pushrod up and down, when you can no longer move it up and down, that is zero lash. If you keep tightening until you can no longer spin the pushrod, like some do, you can get it too tight. and that will keep valves open.

 

[ukstu]

Ok thanks, that may make sense then as i have always done it by twisting. Now i assume the lash needs to be done also while each cylinder is at TDC?

 

[wrench 3]

Also there is more than one TDC per cylinder on each "valve" cycle. All the valves can be adjusted in only two separate positions of the timing cycle. Go to http://boatinfo.no/lib/mercruiser/manuals/mercruiser15.html#/170 page 170 for detailed instructions.

 

[Bondo]

Ok thanks, that may make sense then as i have always done it by twisting. Now i assume the lash needs to be done also while each cylinder is at TDC?

Ayuh,...... Each cylinder, on It's Tdc,.... not Tdc on the crankshaft,.....

To measure lash, back off the rocker arm retaining nut till there is play in the push rod, then tighten it while moving the pushrod up and down, when you can no longer move it up and down, that is zero lash. If you keep tightening until you can no longer spin the pushrod, like some do, you can get it too tight. and that will keep valves open.

Great advice here,..... Exactly how I do it,.....

Whoever wrote 'bout turnin' the push-rod, oughta be hung out to dry,....

 

[ukstu]

Thats great, thank you very much for the advice!

 

[Bt Doctur]

Since I was able to hold a wrench I do it this way
Rotate motor until a intake valve opes and closes, now your coming up on compression and both valves are closed
Tighten rocker until you can`t spin the pushrod with oily fingers and only go a 1/2 turn more .By not recognizing the no slack point (till you can`t spin the pushrod is incorrect but people still do it) and going 3/4 to 1 turn more the valves will be open

 

[Lou C]

Also there is more than one TDC per cylinder on each "valve" cycle. All the valves can be adjusted in only two separate positions of the timing cycle. Go to http://boatinfo.no/lib/mercruiser/manuals/mercruiser15.html#/170 page 170 for detailed instructions.

I did it this way following the procedure in my OMC shop manual. Same process. I suggest using some duct tape to label the valves as either I for intake and E for exhaust first, this way you can't get confused. Of course die hard Chevrolet mechanics would frown on this but for a beginner it helps.....

 

[Scott Danforth]

Whoever wrote 'bout turnin' the push-rod, oughta be hung out to dry,....

It was in a Seloc or Clymer or Haynes manual

 

[Lou C]

Having learned on engines with solid lifters like air cooled VWs and old school Japanese cars, the concept of lash, is actual clearance between the rocker arm and the valve stem, which we measured with feeler gauges, my VW if I recall was .004" intake and .006" exhaust but it is the space between, not the tightness of the rocker arm as it presses against the push rod (you're already at, or past zero lash then!)
On the air cooled VWs if you had them too tight they'd burn out in no time. I used to check em 2x a year usually.

 

[Scott Danforth]

On the air cooled VWs if you had them too tight they'd burn out in no time. I used to check em 2x a year usually.

and if lash numbers started to dwindle, the stems were being pulled from the valves.

 

[wrench 3]

It was in a Seloc or Clymer or Haynes manual

Actually it was General Motors but it was tighten until the drag increased, not until it stopped turning.
The operating range of the self adjuster in the lifter is equal to two turns of the lash adjuster. So one turn down puts it in the center of its travel.

 

[dmitrev]

I know, it's old, but for the people coming here with google My hydraulic lifters was hard as rock - I even was in doubts - are they hydraulic? Removed circlips, (used pressing of the lifter for this) and what I see - viscous mayonnaise inside. All the lifters washed, tomorrow will mount the heads. Motor was with water in the oil, after the repair from professionals...