3.0 Factory Valve Grind Angle

[yrn2fly]

Hello All,

Long time reader first time "poster." I have a 92 Bayliner with a Mercruiser 3.0L & Gen II Alpha I O/D. When I got it it was frozen so I removed the engine and tore it down. I was amazed to find that the engine was new inside and was "frozen" due to a corroded starter. I stripped the head, media blasted and acid etched it.

As I reassemble it I'm inspecting the valves and I'm finding some small corrosion marks on the face/seats on some. Since I have access to a machine shop, can anyone tell me what the factory grinds the valves to? I'm going to do a single angle just as the factory did; I'm guessing 30 or 40-45 degrees.

Any info would be very much appreciated.

Thanks!

Matt R.
San Diego, Khaliforyna

 

[seaslsush]

Re: 3.0 Factory Valve Grind Angle

30 on the intake
45 on the exhaust
the intake valves are not a common size and can cost ya to replace them

 

[Don S]

Re: 3.0 Factory Valve Grind Angle

Click Here and download the OEM service manuals for your engine (#13) and drive (#14). You are going to need them both before you're done.

 

[yrn2fly]

Re: 3.0 Factory Valve Grind Angle

seaslsush/Don S,

Thanks for the replies. I do have one of the manuals but I don't recall it being as detailed as the one at the link; thanks! I was concerned about one of the exhaust valves so I turned a Continental TSIO360 valve down to the same dimensions just in case. But I think the corrosion will clean up ok so hopefully I won't have to use a substitute, even though it's better than factory.

Either way I hope to have it done fairly soon. Debating if I want to cut the seats since they have no corrosion and no signs of wear.

Thanks again guys...

Matt R.

 

[Don S]

Re: 3.0 Factory Valve Grind Angle

I do have one of the manuals but I don't recall it being as detailed as the one at the link;

Somehow I would bet your "Other" manuals are either Seloc, or Clymers. Both are cheap aftermark manuals that only hit the highlights of many engines. The ones I gave yo links to are what Mercruiser sends out to it's dealers. It IS the mercruiser manual, not a cheap aftermarket manual.

 

[Bondo]

Re: 3.0 Factory Valve Grind Angle

Debating if I want to cut the seats since they have no corrosion and no signs of wear.

Ayuh,... Hand lap 'em in,+ See....

 

[Fordiesel69]

Re: 3.0 Factory Valve Grind Angle

All EX valves will have pit marks after 150 hrs. But it is great you have acces to a machine. You can just lap them with both coarse and then fine and it will be like new.

 

[38special]

Re: 3.0 Factory Valve Grind Angle

30 on the intake
45 on the exhaust
the intake valves are not a common size and can cost ya to replace them

A good link for standard size or over sized head and stem valves to spare the cost of seat inserts at an affordable price for the 3.0. Valves for the 181 3.0 can be found under GM van-truck-suv.

http://www.enginetechcatalog.com/de...D=5805348021&OVADGRPID=11609963409&OVNDID=ND1

 

[ENSIGN]

Re: 3.0 Factory Valve Grind Angle

I agree with bondo lap-em.

 

[JustJason]

Re: 3.0 Factory Valve Grind Angle

After I lap them in what I do is flip the head upside down and pour acetone in the combustion chambers, if the acetone doesn't leak out then your good to go.

 

[zbnutcase]

Re: 3.0 Factory Valve Grind Angle

Dont cut the seats unless you have to. Anytime you do you sink the valve and it hurts airflow. And I use isopropyl rubbing alcohol to check seating; cheaper than acetone.

 

[bomar76]

Re: 3.0 Factory Valve Grind Angle

Cutting the seats changes the valve train geometry.

So does grinding the valves.

Hardly anyone ever considers this and just slaps the old pushrods back in.

Pushrod length needs to be checked whenever a valve job is done.

 

[yrn2fly]

Re: 3.0 Factory Valve Grind Angle

Thanks to all of you for some great replies. I did face the valves at 30 and 45 but it appears that the intake seats were not cut at 30 when they overhauled it. So I'm going to bring the head to the shop and cut the seats with a pass or two at 30 degrees.

As for grinding seats or changing valve geometry/airflow, it would take a heck of a lot to see any noticeable change. I put the head on our flow bench & the flow was withing 2 CFM per port/chamber. The runners are cast so poorly that it makes little difference if the valve is .005 lower in it's seat. The real deal is on the intake runners, near the guide area. Put a flow ball at that point and CFM drops or increases quite a bit (at least on a manometer at 10 Hg).

I've been flowing Lycoming and Continental engines for years, some of which are used in the Red Bull aircraft, and cutting seats or valves has little effect unless you cut the face & leave a sharp edge at the flow side (i.e. making the valve too thin). Re-seating is another alternative but I'm not ready to dig into a cast head to heat it & pound in a seat; it's nothing like aluminum.

And I do lap with fine compound, which so far has worked well. The machine does ok but I'd rather do it manually.

Thanks again! I'll keep you posted.

Matt R

 

[bomar76]

Re: 3.0 Factory Valve Grind Angle

As for grinding seats or changing valve geometry/airflow, it would take a heck of a lot to see any noticeable change. I put the head on our flow bench & the flow was withing 2 CFM per port/chamber. The runners are cast so poorly that it makes little difference if the valve is .005 lower in it's seat. The real deal is on the intake runners, near the guide area. Put a flow ball at that point and CFM drops or increases quite a bit (at least on a manometer at 10 Hg).
I've been flowing Lycoming and Continental engines for years, some of which are used in the Red Bull aircraft, and cutting seats or valves has little effect unless you cut the face & leave a sharp edge at the flow side (i.e. making the valve too thin).
Matt R

You didn't read (or understand) what I posted.
Here is a lesson in pushrod engine building:

Recutting valve seats and grinding valves changes the VALVE TRAIN GEOMETRY.
I said nothing about changing flow.
Anytime you grind a valve OR cut a seat it changes how far the valve stem protrudes above the spring seat.
This changes the installed height of the spring and the correct pushrod length (because the valve stem is now sticking up higher above the spring seat), both of which have major effects on the valve train GEOMETRY and also the valve spring rate.

Valve springs may need shimmed to the correct installed height, and usually a checker spring is installed to accurately determine the correct pushrod length required once the springs are brought to the correct installed height. It can be done without a check spring but I think it is a PITA to do without. An adjustable pushrod is used to determine correct rocker to valve contact and then measured to determine the exact pushrod length required.

 

[bomar76]

Re: 3.0 Factory Valve Grind Angle

Oh...and as an aside....Milling a head, decking a block, and of course changing a cam also changes the valve train GEOMETRY.

 

[seaslsush]

Re: 3.0 Factory Valve Grind Angle

that is true for solid cam followers
I think that he will have hydraulic lifters and they
should self adjust for the difference the seats are cut

which brings up the question of adjusting hydraulic valve lifters
I set mine at 0 to 1/8 turn and have had good luck so far....

 

[bomar76]

Re: 3.0 Factory Valve Grind Angle

that is true for solid cam followers
I think that he will have hydraulic lifters and they
should self adjust for the difference the seats are cut

Not true.

 

[mariner1900]

Re: 3.0 Factory Valve Grind Angle

Mercruiser manaul #13 specifies 45 degrees for both inlet and exhaust valve. Manual also specifies 46 degrees for the seats.

It is now common practise, by a majority of engine manufacturers, to grind the seat and valves at different angles. This is done to achieve a very fine contact point with the contact face widening as the engine is run. There is normally no need for lapping if the valve and seat are ground properly as lapping is causing wear on the valves and seats before you even assemble the engine. The valve/seat contact face is normally just checked with "bearing blue" to ensure full contact. I have not 'lapped" valves for at least 15 years, on many makes and sizes of engines, due to the 2 angle grinding method now preferred.

Whilst what Bomar states about the valve train geometry changing when you grind the valves and seats, if the change is that large that is has an effect then I would suggest that it is time to replace the valves and or seats.

 

[yrn2fly]

Re: 3.0 Factory Valve Grind Angle

bomar76, et al,

You're right in that I misread your post. I guess its the confluence of talk about flow, geometry, etc. In my case I dialed the valve height at the stem. I ground the face at 45 & redialed it with a net difference of .0015. On a fixed rocker configuration I typically find that facing a valve requires a .030 over pushrod. But given that the fulcrums aren't pedestal type they can be adjusted (and the 3.0 uses hydraulic lifters) to take up any change.

Facing the valves (or even cutting seats within reason) might change geometry, but it'd be minimal. And even if it were more measurable the effects would be difficult to detect. But I do agree that too much grinding or facing can have more significant effects like thinning or warping of the face. Too much and there is the issue of pushrod length, etc.

As for 2 or 3 angle cuts to the seat I'm thinking... this is a boat engine not a rocket motor or turbine so... a single angle valve job for a plain 3.0 is plenty. The intakes are straight-shot style so 3-angle valve jobs are not going to offer significant improvement. I flowed my head before grinding the valves and I will again after. I'll post any change in CFM but I doubt there will be any.

Thanks!

 

[bomar76]

Re: 3.0 Factory Valve Grind Angle

Whilst what Bomar states about the valve train geometry changing when you grind the valves and seats, if the change is that large that is has an effect then I would suggest that it is time to replace the valves and or seats.

Again, anytime anything is done to the valve train the pushrod lenth needs to be checked.
That is one of the many differences between throwing an engine together and being happy it runs and assembling a engine.