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Omc cylinder head

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MortenBayliner

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Can someone please help!!!
I have to OMC cylinder heads on the table
they should both be for a 5L omc small block 305
they both have the number stamped into them 14102187
but one have GM1 and the other one have GM2 stamped into it
what is the diffrence on these head, will they both fit on my omc 5L 1988 small block V8???

best Morten
 
MortenBayliner said:
Can someone please help!!!
I have to OMC cylinder heads on the table
they should both be for a 5L omc small block 305
they both have the number stamped into them 14102187
but one have GM1 and the other one have GM2 stamped into it
what is the diffrence on these head, will they both fit on my omc 5L 1988 small block V8???

best Morten
Click to expand...

Morten, by 1988 the Marine version SBC was being fitted with the GM full dished pistons.
The SBC cylinder head combustion chamber volume must a correct match for the 5.0L bore/stroke/piston profile.

Your cylinder head casting number indicates a chamber volume of 58cc.


It will be very important to know which chamber volume is a match for your 1988 SBC before using these 14102187s.



.
 
MortenBayliner said:
The cylinder head originaly mounted on my engine was the 14102187 GM1
my new cylinder head is 14102187 GM2, can I use this on my engine?
Click to expand...
The only diffrence between the two cylinder heads i the number “GM1” in the original cylinder head, and “GM2” in the new cylinder head.
the valves on the two cylinder heads are also diffrent, the “GM1” valves are more thick.
valves that belong to there cylinder head, stay with there cylinder head, I do not mix the valves from GM1 to GM2

my suspicion is that GM2 is a socond generation cylinder head, a replasement for GM1, and that this cylinder head can be used to replace the older GM1, but valves from one type should not be used on the other type.
Since this would change the volume.
 
MortenBayliner said:
The only diffrence between the two cylinder heads i the number “GM1” in the original cylinder head, and “GM2” in the new cylinder head.
the valves on the two cylinder heads are also diffrent, the “GM1” valves are more thick.
When seats and valves have been dressed to their limits, the valves may rest deeper into the casting, so it may appear that the valves have lost thickness.
Is this what you may be seeing?

valves that belong to there cylinder head, stay with there cylinder head, I do not mix the valves from GM1 to GM2

my suspicion is that GM2 is a socond generation cylinder head, a replasement for GM1, and that this cylinder head can be used to replace the older GM1, but valves from one type should not be used on the other type.
Since this would change the volume.
See my ** below!
Click to expand...



Morten, using the "out in the shop" automotive SBC cylinder head casting number guide, the 14102187 (not sure about GM1 or GM2) casting shows up as:

Used for the 305 cu in (5.0L)
Used during 1987 thru 1995
It has the small 1.50" exhaust valves and 1.84" intake valves.
The combustion chamber volume is listed as 58cc.

I am not able to tell you if this casting was used as OEM for the 1988 OMC Marine version 5.0L SBC.


** If you are certain that the 14102187 GM1 was original, then I would suggest finding another GM1 casting..... or take them both into a good automotive machine shop and ask what the difference is.


Here is what's important since it sounds as though you are replacing one cylinder head ONLY:

intake manifold bolt hole angle must be the same as the GM1.
combustion chamber volume should be the same, and should be the same as what the OEM used in 1988.
intake and exhaust valves should be of same diameter.
all valve seats should be hardened seats.
compressed head gasket thickness should be the same on both sides (IMO, both heads should be R&R'd).


Lastly, if you have the replacement cylinder head re-worked, I would do the same to the other cylinder head.


Make sure that you use the 8 stop static cam follower adjustment procedure when going back together.







.

 
Last edited:
Thank's Ricardo for your detailed reply.
Yes I'm sure your right that my valves looks different because they have been dressed to the limit on the GM2 cylinder head.
The number seems to explain what cylinder head it is, 14102187, if it is named GM1 or GM2 might not make a difference.
I have mounted the new rebuild GM2 cylinder head, and measured compression 9-10 bar on all cylinders, I accept this, and will start her up in a few days when I finished mounting everything.
I do not know what "8 stop static cam follower adjustment procedure" is, I hope I did not make any mistake not doing this,
I tighten the cylinder head after OMC procedure to 90 NM
Best
Morten
 
The 8 stop procedure requires that you begin with number one cylinder at TDC C/S. (C/S = compression stroke)
Both intake and exhaust cam follower plunger depths can be set at this time. Follow the OEM recommended fraction of one turn past zero lash!

The next cylinder in the firing order will be number 8.
Turn the crankshaft 90 degrees from whet you were, and you are at #8 TDC C/S.
Adjust both intake and exhaust as you did for #1.

The next one will be number 4.
Again, turn the crankshaft 90 degrees.
Adjust both intake and exhaust.

Do the same for each cylinder right down the firing order until you come back to #1!


The 8 stop is goof proof and is much more accurate!


.
 
Retoque after a warmup and a cool down, also check youtube for further help,but be careful,alot of shadetree mechanics out there
 
Hi Ricardo
So the 8 Stop procedure is all about setting the valves, right?
I did not do the 8 stop, I followed the YouTube "A1 Auto" made (https://www.youtube.com/watch?v=wFgLtP_NSsg&t=2996s)
TDC: (setting)
Intake 1,2,5,7
Exaust 1,3,4,8
Then move 360 to TDC exaust (setting)
Intake 3,4,6,8
Exaust 2,5,7

You do not find this method good, ?? , should I redo it the 8 stoop way?

If the engine will fire up (witch I hope it will), I will set the ignition timing.
1. Block the vacuum hose to the carburetor
2. Rotate the distributor until my timing gun, show the mark at TDC -10degree
Or do you have a different (not to complicated) procedure here to?
 
1. Block the vacuum hose to the carburetor
Click to expand...

Ayuh,..... Donno what you've got for a distributor, but it Ain't a Marine unit,.....

Boat distributors do Not have a vacuum connection,......
 
........................
MortenBayliner said:
Hi Ricardo
Good morning!

So the 8 Stop procedure is all about setting the valves, right?
Well....... it is a misnomer to think that we adjust valves. There is no valve adjustment nor are there any lifters.
(these are carry-over terms from years past)

Your hydraulic cam "followers" incorporate a hydraulic plunger within the body of the follower.
This plunger rides on a cushion of pressurized engine oil.
The plunger (aka piston) has a check valve underneath it to prevent oil leakage during camshaft lift.

The rocker arm tip is to have NO slack between itself and the valve stem while the camshaft lobe is at bottom of the base circle.
When we have removed the slack, this is ZERO valve lash.

Once ZERO lash has been achieved (cam lobe at bottom circle), we give the rocker arm stud nut an additional fraction of one turn (it may be 1/4 turn, it may be 1/2 turn or it may be 3/4 turn, depending on what the OEM specs call for)

This additional fraction of a turn sets the push rod into the cup of the cam follower plunger.
The cup depresses the plunger to a prescribed depth.

Each of these adjustments must be made while each cam lobe is at the bottom of base circle. The 8 stop procedure ensures that each pair of cam lobes (1 intake/1 exhaust) are at bottom of base circle.


Each plunger has a potential travel of .100" to .130", or so.
The goal is to place the hydraulic plunger at/near a 1/2 way point between bottoming out and topping out.


I did not do the 8 stop, I followed the YouTube "A1 Auto" made ( https://www.youtube.com/watch?v=wFgLtP_NSsg&t=2996s )
These are the guys who get people in trouble.
I would NEVER suggest using the 2 or 3 stop procedure.


TDC: (setting)
Intake 1,2,5,7
Exaust 1,3,4,8
Then move 360 to TDC exaust (setting)
Intake 3,4,6,8
Exaust 2,5,7

You do not find this method good, ??
NO! It is NOT good! At best, it is a lazy man's short cut!

, should I redo it the 8 stop way?
You do what you want to..... if it was ME, yes!

If the engine will fire up (witch I hope it will), I will set the ignition timing.
1. Block the vacuum hose to the carburetor
There should be NO vacuum hose to the carburetor.

2. Rotate the distributor until my timing gun, show the mark at TDC -10degree
Or do you have a different (not to complicated) procedure here to?

Bring the crankshaft around to #1 TDC C/S.
With the ignition ON, and with a good spark plug inserted into #1 plug wire (plug body must make good metal contact), rotate the distributor CCW until you see a spark event.
Gently lock it down.
Start engine and set BASE advance.
Click to expand...
 
MortenBayliner said:
Did everything you recommended and also used 8 stop procedure.
And it runs like a charm :)
Thanks alot
Click to expand...

You are very welcome, and I'm glad to see that you used the 8 stop.

With the 2 or 3 stop, it is always best to go back through them dynamically.
With the 8 stop, we rarely need to go back through them..... if at all.


.
 
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