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Mechanical Valve timing - 2.8L in 86XJ

Anyone know the mechanical sequence (in degrees) for a 2.8L GM with
externally balanced crank?

GM doesnt seem to have the specs. in their archives (?????????). The
local Stealership has no idea of what I'm talking about - not
surprised.

Am looking for at what degree of crankshaft rotation the Intake and
Exhaust valves of #1 begins to open and what is the degree at full
closed.
I have the dwell, the lift, ....but not the degrees (vs. TDC) to
open/close.

Note to Mike Romain ---- yup, I guess you were right that the
mechanical timing was off. All the damn 'indicators' lined up
correctly ... but the engine is still running quite retarded. It HAS
to be the mechanical valve timing.

Other question: if I find that the mechanical timing is indeed off
(probably due to a 'stack-up' of tolerances. How does one readjust? A
long time ago, I remember watching someone use a 'special bushing set'
on the vibration damper, which allowed advancing or retarding the
mechanical timing. Seems that Alzheimers is beginning to catch up as
I cant quite remember .............

Thanks for any input.

--
RichH.

Re: Mechanical Valve timing - 2.8L in 86XJ

I would guess as gutless as I heard this engine is, it's probably
running about thirteen degrees forward as this Crane SMOG replacement:
http://www.cranecams.com/index.php?s...11&lvl=2&prt=5
The cam is chain driven so there's no adjustment, other than it
probably needs replacement.
How about the 3.4 swap:
http://www.off-road.com/jeep/cheroke...28-34swap.html and
http://www.rebuiltcarengines.com/ce06.html
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/

Rich Hampel wrote:
>
> Anyone know the mechanical sequence (in degrees) for a 2.8L GM with
> externally balanced crank?
>
> GM doesnt seem to have the specs. in their archives (?????????). The
> local Stealership has no idea of what I'm talking about - not
> surprised.
>
> Am looking for at what degree of crankshaft rotation the Intake and
> Exhaust valves of #1 begins to open and what is the degree at full
> closed.
> I have the dwell, the lift, ....but not the degrees (vs. TDC) to
> open/close.
>
> Note to Mike Romain ---- yup, I guess you were right that the
> mechanical timing was off. All the damn 'indicators' lined up
> correctly ... but the engine is still running quite retarded. It HAS
> to be the mechanical valve timing.
>
> Other question: if I find that the mechanical timing is indeed off
> (probably due to a 'stack-up' of tolerances. How does one readjust? A
> long time ago, I remember watching someone use a 'special bushing set'
> on the vibration damper, which allowed advancing or retarding the
> mechanical timing. Seems that Alzheimers is beginning to catch up as
> I cant quite remember .............
>
> Thanks for any input.
>
> --
> RichH.

Re: Mechanical Valve timing - 2.8L in 86XJ

Thanks for the info

Its not as gutless as it seems and for the purpose that I want .....
cruise at 65-70mph and with good fuel economy. You just need to
'finesse' it and make sure that all the eco-nazi crap is working
perfectly. Most other 2.8s that Ive had in this XJ deliver about 22-23
mpg at cruise.

Thanks again

Re: Mechanical Valve timing - 2.8L in 86XJ

"Rich Hampel" <RhmpL33@nospam.net> wrote in message
news:300620041215068054%RhmpL33@nospam.net...
> Anyone know the mechanical sequence (in degrees) for a 2.8L GM with
> externally balanced crank?
>
> GM doesnt seem to have the specs. in their archives (?????????). The
> local Stealership has no idea of what I'm talking about - not
> surprised.
>
> Am looking for at what degree of crankshaft rotation the Intake and
> Exhaust valves of #1 begins to open and what is the degree at full
> closed.
> I have the dwell, the lift, ....but not the degrees (vs. TDC) to
> open/close.
>
> Note to Mike Romain ---- yup, I guess you were right that the
> mechanical timing was off. All the damn 'indicators' lined up
> correctly ... but the engine is still running quite retarded. It HAS
> to be the mechanical valve timing.
>
>
> Other question: if I find that the mechanical timing is indeed off
> (probably due to a 'stack-up' of tolerances. How does one readjust? A
> long time ago, I remember watching someone use a 'special bushing set'
> on the vibration damper, which allowed advancing or retarding the
> mechanical timing. Seems that Alzheimers is beginning to catch up as
> I cant quite remember .............
>
> Thanks for any input.
>
> --
> RichH.

Almost all of GM's modern engines utilize a wide lobe center angle for
emissions purposes and a broader torque curve. Generally the peak lift
occurs on the intake at about 110-112 degrees after top dead center. It is a
common "trick" to advance the camshaft to boost low end torque slightly, and
to lower the torque peak RPM of the engine. Be careful about using valve
opening and closing events for cam timing, as most specs vary depending on
who wrote them. Advertised duration as it is known, is an almost useless
number in the real world.

I am assuming that you have a degree wheel to check the cam timing. If so,
do it the right way and find out the intake lobe centerline. This is done by
finding true TDC first. Put the wheel on the balancer or crank and put a
dial indicator on the piston. Bring the engine to apparent TDC and zero the
indicator and the pointer on the wheel. Now turn the engine in its normal
rotation direction (always do this to take up the slack in the bearings and
timing components) until the piston is .100 down in the cylinder. Take a
reading on the wheel. Now go the other way past TDC and past .100 down in
the cylinder. Now bring the piston up until the indicator reads .100 (again,
do it this way to take up all the slack). Take another wheel reading. If
they are the same, then you have true TDC. If not, then adjust the pointer
by half the difference of the 2 readings. Repeat the .100 down check until
you have the same readings.

Once the wheel is set, you can put the indicator on the #1 intake lifter. Be
sure that the lifter plunger does not move during the measurements. I
usually use a solid lifter to avoid this, but it can be done with a
hydraulic if you're careful. Turn the engine past TDC until the lobe reaches
peak lift. Zero the indicator. Now turn the engine until the indicator moves
..050 down and take a reading. Go back past peak lift and .050 down (again,
go past this point and come back to it if you are turning the engine counter
clockwise). Take a reading at this point. Add these 2 number up and divide
by 2. This will be your intake lobe centerline. The number should end up
somewhere in the range of 106 to 110 degrees.

HTH

Chris