Deck height

Hi all !

What would be a problem if any with rebuilding a lycoming case with a
deck height out of spec.
As a matter of fact How does one measure a deck ?
I am assuming that the deck is where the cyl barrel is bolted down to.
If so then I would assume that haveing a slightly smaller height would
in turn allow the piston to go a smidge further in the cylinder. If the
valve train was fixed then the valve would not seat fully. However these
things have hydraulic tappets that will take up some play yes ?


I have looked in my 0-360 overhaul manual but have not found anything on
it.

Thanks in advance
Sean Trost
Mj-5 in restoration

What would be a problem if any with rebuilding a lycoming case with a
deck height out of spec.
As a matter of fact How does one measure a deck ?
I am assuming that the deck is where the cyl barrel is bolted down to.
If so then I would assume that haveing a slightly smaller height would
in turn allow the piston to go a smidge further in the cylinder. If the
valve train was fixed then the valve would not seat fully. However these
things have hydraulic tappets that will take up some play yes ?


I have looked in my 0-360 overhaul manual but have not found anything on
it.

Thanks in advance
Sean Trost
Mj-5 in restoration

Depends on how much out of spec.. A 32nd would probably be OK.
Deck height is measured by first cleaning and honing flat the split side of the
engine case. Also clean and hone flat the surfaces the cylinders bolt to.
Lay the split side on a layout/inspection plate and measure from the cylinder
flange surfaces down to the layout plate using a depth micrometer with the
proper length blade. A good machine shop can do this for you in 5 minutes.
Yes, the hyd. lifters have a good bit of range, however, you should still check
the dry dimensions of the lifters when assembling the engine. Do this by
collapsing the lifters and measuring the gap between the valve stem end and
the rocker arm when the vavles are closed. Should tell you how in the manual.
IIRC, Lycomings have a little tighter tolerance, 1/32 to 3/32. Continentals
tolerance is greater. 1/16 to 3/16. But check your manual.
Good luck,


Warren

Sean Trost wrote in message r.com...
Hi all !

What would be a problem if any with rebuilding a lycoming case with a
deck height out of spec.
snip

Deck height is the distance from the crankshaft centerline to the cylinder
barrel mounting surface. Machine shops that overhaul cases have a fixture
for taking this measurement. Once a case has been overhauled to the point
where it is below critical deck height several undesirable things happen.
As you mentioned, piston TDC depth in the cylinder might be so great that
it hits the head or one of the valves. Hydraulic lifter dynamic adjustment
range could be exceeded and the valve clearance not properly maintained
under all thermal conditions by the lifter. But there is also accessory
gear problems too. When the mating surfaces of a case are planed flat the
crank and cam bearing holes are made oval. These then need to be line
bored to make them perfectly round again. This effectively moves the
crank and cam centerlines outward in each case half. If there are gear
driven accessories on the back in fixed locations (e.g. mags, etc) the
gear teeth on the crank and/or cam may now be meshed to deeply with those
on the accessories. All of these issues factor in the the determination
of critical deck height and render a case beyond its usefull life.

Any reputable case overhauler like Divco or Ajax should be able to tell
you what the critical deck dimension is for your engine case.

Now if you were rebuilding a VW engine, which doesn't have an accessory
case and uses solid lifters, you would simply use cylinder barrel shims
to account for deck height. But I digress...

Gary

GaryP wrote:

Sean Trost wrote in message r.com...
Hi all !

What would be a problem if any with rebuilding a lycoming case with a
deck height out of spec.
snip

Deck height is the distance from the crankshaft centerline to the cylinder
barrel mounting surface. Machine shops that overhaul cases have a fixture
for taking this measurement. Once a case has been overhauled to the point
where it is below critical deck height several undesirable things happen.
As you mentioned, piston TDC depth in the cylinder might be so great that
it hits the head or one of the valves. Hydraulic lifter dynamic adjustment
range could be exceeded and the valve clearance not properly maintained
under all thermal conditions by the lifter. But there is also accessory
gear problems too. When the mating surfaces of a case are planed flat the
crank and cam bearing holes are made oval. These then need to be line
bored to make them perfectly round again. This effectively moves the
crank and cam centerlines outward in each case half. If there are gear
driven accessories on the back in fixed locations (e.g. mags, etc) the
gear teeth on the crank and/or cam may now be meshed to deeply with those
on the accessories. All of these issues factor in the the determination
of critical deck height and render a case beyond its usefull life.

Any reputable case overhauler like Divco or Ajax should be able to tell
you what the critical deck dimension is for your engine case.

Now if you were rebuilding a VW engine, which doesn't have an accessory
case and uses solid lifters, you would simply use cylinder barrel shims
to account for deck height. But I digress...

Gary

Concise and coherent explanation.

In fact, my only objection (at all!) is in reference to the VW engine
in the last paragraph.

There are several accessory cases available for the VW.
Most are single ignition setups, but I've seen at least one that
supported dual mags.

Thanks, Gary.
Ya done good.

Respectfully,

Richard Lamb

thanks all for the assist !
Will have to pass on this one and look for a better deal.
Sean Trost

Sean Trost wrote:
Hi all !

What would be a problem if any with rebuilding a lycoming case with a
deck height out of spec.
As a matter of fact How does one measure a deck ?
I am assuming that the deck is where the cyl barrel is bolted down to.
If so then I would assume that haveing a slightly smaller height would
in turn allow the piston to go a smidge further in the cylinder. If the
valve train was fixed then the valve would not seat fully. However these
things have hydraulic tappets that will take up some play yes ?


I have looked in my 0-360 overhaul manual but have not found anything on
it.

Thanks in advance
Sean Trost
Mj-5 in restoration

Richard Lamb wrote in message ...
Concise and coherent explanation.

In fact, my only objection (at all!) is in reference to the VW engine
in the last paragraph.

There are several accessory cases available for the VW.
Most are single ignition setups, but I've seen at least one that
supported dual mags.

Thanks, Gary.
Ya done good.

Respectfully,

Richard Lamb

Doh! I knew I shouldn't have digressed g.
I've never seen an accessory case for a VW beyond the Great Plains variety
which capped off the flywheel flange to accomdate a webbed ring gear for a
starter and crank driven mag. Nothing affected by deck height using this
arrangement. But if someone out there makes an accessory case for a VW
with a gear driven dual mag set up, then that is a different story and I
stand corrected.

Regards,
Gary