[E-Type] piston design for engine rebuild

Hi All,

I am in the process of having my engine rebuilt. The engine
will be returned to 9.0:1 compression when done. I’m going
to have the pistons machined by JE to compensate for the rod
remachining, block/head shaving, etc. that has occured over
the past 45 years. That is: we are measuring all
dimensions and ccing the head, then designing the piston to
return the car to the correct ratio.

Before I place the order I’d like to confirm one parameter:

What shoulder height (distance from top of block to top of
piston shoulder) would you recommend? Since the pistons are
being machined for me I can pick any value that I want.

I was planning to design the pistons for 1 mm step height.
But perhaps there is some Jag specific reason why I should
choose a different design point?

Thanks,

Larry–
Larry Wade 62 OTS, La Canada, California USA
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In reply to a message from Larry Wade sent Mon 18 Jun 2007:

‘’…designing the piston to return the car to the correct
ratio…’’

Wow, That sure sounds expensive!

I had my head and block machined and then CC’d the engine,
myself.(My machine shop lent me the graduated titration tube
& ‘‘stuff’’) Then I used Ray Livingston’s formula and
installed a .085’’ Cometic MLS Gasket with regular NOS 9.0:1
at .030’’ O.S. pistons that I bought on eBay for less than
$100…Maybe there’s a better way of doing the job, but if I
had to do it over again…I’d hope to do it the same
way…My machine shop checked out pistons when they fitted
new small end bushes…

Abner–
The original message included these comments:

will be returned to 9.0:1 compression when done. I’m going
to have the pistons machined by JE to compensate for the rod
remachining, block/head shaving, etc. that has occured over
the past 45 years. That is: we are measuring all
dimensions and ccing the head, then designing the piston to
return the car to the correct ratio.


lilAbner
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I was planning to design the pistons for 1 mm step height.
But perhaps there is some Jag specific reason why I should
choose a different design point?

I don’t know Larry, 1mm sounds pretty dodgey/non-stock/un-Jaguar to
me, shouldn’t you go with 0.039370079" instead? Or maybe 1/25th of an
inch?

:wink:

–chuck goolsbee
65ots, 1E10715
arlington, wa, usa
http://chuck.goolsbee.org

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In reply to a message from Larry Wade sent Mon 18 Jun 2007:

Hi Larry,

The distance from the flat part of the piston (not the dome) to the
head should be a minimum of .040’’. So if your gasket is .035’’
compressed the piston should be .005’’ in the hole. I like to
use .045’’ so I can surface the block if need be at a later rebuild.
That clearance will give you a little bit of mixture swirl at TDC
when the piston squeezes the mixture out of the crevice. Since the
XK combustion chamber is inefficient it needs the help. More power
and less detonation from a more homogeneous mixture. If you go more
than .060’’ the advantage is lost. If you go to .025’’ the piston
will hit the head at high rpm from rod stretch.

I find it easier to get the pistons made, do a trial assembly and
measure, and then deck the block to get it right. As you can see
there isn’t a lot of room for error.

Regards,
Rich Olson '67 OTS–
The original message included these comments:

I am in the process of having my engine rebuilt. The engine
will be returned to 9.0:1 compression when done. I’m going
to have the pistons machined by JE to compensate for the rod
remachining, block/head shaving, etc. that has occured over
the past 45 years. That is: we are measuring all
dimensions and ccing the head, then designing the piston to
return the car to the correct ratio.
Before I place the order I’d like to confirm one parameter:
What shoulder height (distance from top of block to top of
piston shoulder) would you recommend? Since the pistons are
being machined for me I can pick any value that I want.


Richard Olson
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In reply to a message from Richard Olson sent Tue 19 Jun 2007:

I second Richard’s suggestion and you’ll need to sacrifice a headgasket or use your old one if it’s the identical brand to do the checking, as you’ll need to torque eveything down to spec. Plastigauge has its uses and checking squish clearances is one of the better ones. It is definitely worth taking time over, although for road motors many of us just live with however it turns out. But if the engine has been machined or you really wan’t the satisfaction of knowing it’s ‘right’ then you can definitely improve on factory generous margins of error. Don’t cut it ‘too’ fine in case you miss a gear some day but on race engines it’s nice to see how clean it stays in the squish turbulencce area as there’s no carbon build-up.–
Peter Crespin 66E, 76 DD6 Coupe, 84 DD6, 85 XJS 5sp convert
Cambridge, United Kingdom
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In reply to a message from PeterCrespin sent Tue 19 Jun 2007:

Thanks Rich and Peter!

That is somewhat different than I’d been thinking. I was
planning to use a 0.040’’ cometic gasket. Any idea how much
it will squish?

I hate to trash one just to find out. Maybe I’ll have to?

As to the cost: it is not that much more to get really good
pistons made than the AE ones cost (about $60 each including
the rush fee). I found that my old AE’s varied fairly
significantly in size. Now they won’t. Going this route
also allows me to adjust for the various block and head
shavings plus a rod remachining over the course of the car’s
life…while still getting the compression right.

Cheers,

Larry–
The original message included these comments:

In reply to a message from Richard Olson sent Tue 19 Jun 2007:
I second Richard’s suggestion and you’ll need to sacrifice a headgasket or use your old one if it’s the identical brand to do the checking, as you’ll need to torque eveything down to spec. Plastigauge has its uses and checking squish clearances is one of the better ones. It is definitely worth taking time over, although for road motors many of us just live with however it turns out. But if the engine has been machined or you really wan’t the satisfaction of knowing it’s ‘right’ then you can definitely improve on factory generous margins of error. Don’t cut it ‘too’ fine in case you miss a gear some day but on race engines it’s nice to see how clean it stays in the squish turbulencce area as there’s no carbon build-up.

Peter Crespin 66E, 76 DD6 Coupe, 84 DD6, 85 XJS 5sp convert
Cambridge, United Kingdom


Larry Wade 62 OTS, La Canada, California USA
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In reply to a message from Larry Wade sent Tue 19 Jun 2007:

Rods Re-machined? What is that? Don’t you just replace the
small end and large end bush/bearings (wrist and crank)??
No change in length & no need to compensate elsewhere.

I would machine the head and deck if necessary (Some frown
on machining the head and TWIST it back into shape) Then CC
the chambers and then plan the Cometic Gasket & etc.
You might do well to buy the Cometic Gaskets from Terry’s
Jaguar…If you ask Bill Terry (himself) he might also lend
you some guidance…When I asked him for his help he called
the owner of Cometic to get my questions answered…

Abner–
The original message included these comments:

shavings plus a rod remachining over the course of the car’s
life…while still getting the compression right.


lilAbner
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Abner,
I think Larry is referring to what many race shops call dusting the
big end of the rod. The shop that did the machine work on my engine
back in in 91 explained the procedure as basically being the same as
line honing or boring of the main bearing saddles. A very small
amount is accurately ground from the mating surface of the cap, the
cap reinstalled on the rod and then honed to a specified dimension to
correct any slight distortion of the bore of the big end…
Bob
889076
Plymouth, Mi.On Jun 19, 2007, at 9:30 AM, lilAbner wrote:

In reply to a message from Larry Wade sent Tue 19 Jun 2007:

Rods Re-machined? What is that? Don’t you just replace the
small end and large end bush/bearings (wrist and crank)??
No change in length & no need to compensate elsewhere.

I would machine the head and deck if necessary (Some frown
on machining the head and TWIST it back into shape) Then CC
the chambers and then plan the Cometic Gasket & etc.
You might do well to buy the Cometic Gaskets from Terry’s
Jaguar…If you ask Bill Terry (himself) he might also lend
you some guidance…When I asked him for his help he called
the owner of Cometic to get my questions answered…

Abner


The original message included these comments:

shavings plus a rod remachining over the course of the car’s
life…while still getting the compression right.


lilAbner
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In reply to a message from Robert Stevenson sent Tue 19 Jun 2007:

Bob,
And also to ensure all the rods are precisely identical length.–
Ray Livingston - '64 OTS Santa Cruz, CA
Santa Cruz, CA, United States
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In reply to a message from Robert Stevenson sent Tue 19 Jun 2007:

OK…It doesn’t matter how many machinations are involved,
in the fitting of new bush/bearings.
It doesn’t alter the compression and no compensation is
required elsewhere.
In the end, I suppose, if you’re happy doing all this GOOD
stuff, then, by all means…

Abner–
The original message included these comments:

I think Larry is referring to what many race shops call dusting the
big end of the rod. The shop that did the machine work on my engine
back in in 91 explained the procedure as basically being the same as
line honing or boring of the main bearing saddles. A very small
amount is accurately ground from the mating surface of the cap, the
cap reinstalled on the rod and then honed to a specified dimension to
correct any slight distortion of the bore of the big end…


lilAbner
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In reply to a message from lilAbner sent Tue 19 Jun 2007:

Actually the commpression is affected.

The bearings were wearing the rods unevenly: Basically the
hole for the bearings was machined too large by the
boneheads who did the job the first time. So the bearings
were slipping around some in the rod. They way you fix this
is to skim off some of the rod at the bolt interface and
then hone a new round hole. The consequence of this is to
slightly shorten the connecting rod. That in turn affects
the piston position and hence the compression. Per Ray’s
spreadsheet a change of 4 mils at TDC will change the
compression ratio by about 0.1:1.

As to good stuff: let’s hope so. Hopefully the engine will
be balanced, smooth and ready for 100K of hard driving when
done! Then it will all be worth while.

By the way, did you know that pigs fly?

Trying hard to make the best of a bad situation,

Larry–
The original message included these comments:

OK…It doesn’t matter how many machinations are involved,
in the fitting of new bush/bearings.
It doesn’t alter the compression and no compensation is
required elsewhere.
In the end, I suppose, if you’re happy doing all this GOOD
stuff, then, by all means…
Abner


Larry Wade 62 OTS, La Canada, California USA
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Right you are Ray! As you and others on this list know there is a
huge difference between engine re-builders. The shop that I dealt
with for years, Holbrook Engineering now closed due to the owners
death, built mainly hot street and drag racing engines and had been
in that business for probably 30+ years and truly knew the in’s and
out’s of engine rebuilding for power and reliability. Sooo- if “Uncle
Carl” recommended that something should be done, and he would always
explain why, I had them do it. Carl became a friend and besides
missing him I have not yet found another shop that I trust the way
that I did his!
Bob
889076
Plymouth, Mi.On Jun 19, 2007, at 12:11 PM, Ray Livingston wrote:

In reply to a message from Robert Stevenson sent Tue 19 Jun 2007:

Bob,
And also to ensure all the rods are precisely identical length.

Ray Livingston - '64 OTS Santa Cruz, CA
Santa Cruz, CA, United States
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In reply to a message from Larry Wade sent Tue 19 Jun 2007:

Larry,

You mean to say that the bearings were ‘‘flopping around’’???

‘’…Boneheads…’’ The bane of ‘‘Jaguardom’’

What IS important here is that you have a great engine when
your done…Don’t let any boneheads touch it…

I am sure you have read some of the horror stories on the
list…Boneheads and Jaguars don’t mix…

Abner–
The original message included these comments:

The bearings were wearing the rods unevenly: Basically the
hole for the bearings was machined too large by the
boneheads who did the job the first time. So the bearings


lilAbner
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In reply to a message from lilAbner sent Wed 20 Jun 2007:

Abner,
Larry hasn’t simply read the horror stories, he’s living one of
his own right now…–
The original message included these comments:

I am sure you have read some of the horror stories on the
list…Boneheads and Jaguars don’t mix…
Abner


Ray Livingston - '64 OTS Santa Cruz, CA
Santa Cruz, CA, United States
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In reply to a message from Ray Livingston sent Wed 20 Jun 2007:

Ray,

Right now, I am in a state of cautious optimism…
AFTER I had decided to do the engine reassembly by myself I
started poring over some of the horror stories. You know,
like Lynn’s tale and then I think you had a bummer and Chuck
and etc. I started to feel like I HAD to it myself.

I had that brand new leaky waterpump…I have a rattling
‘‘dust cover’’ on the bell housing… Ride height
adjustment…I think I can deal with problems like that…I
am kinda holding my breath…but so far so good…

Abner–
lilAbner
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In reply to a message from lilAbner sent Wed 20 Jun 2007:

Abner,
If you’re even a little competent, you can’t help but do better
than some of the places others have had the misfortune to have work
on their Es.
But, I’ll keep my fingers crossed for you, just in case! :-)–
The original message included these comments:

Ray,
Right now, I am in a state of cautious optimism…
AFTER I had decided to do the engine reassembly by myself I
started poring over some of the horror stories. You know,

lilAbner


Ray Livingston - '64 OTS Santa Cruz, CA
Santa Cruz, CA, United States
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In reply to a message from Ray Livingston sent Wed 20 Jun 2007:

Larry,
I am sorry to hear that you are on the ‘‘LIST’’ too…
I had no idea. Now I can feel badly for yourself, and Lynn
and the other fellows…
I know you will get the engine sorted out, it sounds like
you have a solid action plan.

Abner–
The original message included these comments:

Larry hasn't simply read the horror stories, he's living one of 

his own right now…


lilAbner
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I’m proud of you Abner, wish I had one it that way!
Cheers,
LynnOn Jun 19, 2007, at 7:42 PM, lilAbner wrote:

In reply to a message from Ray Livingston sent Wed 20 Jun 2007:

Ray,

Right now, I am in a state of cautious optimism…
AFTER I had decided to do the engine reassembly by myself I
started poring over some of the horror stories. You know,
like Lynn’s tale and then I think you had a bummer and Chuck
and etc. I started to feel like I HAD to it myself…

Abner

Lynn G
73 2+2 (Pearle)
68 OTS (Emmy)
66 Spitfire (Sweet Pea)
Boise, ID USA

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In reply to a message from Larry Wade sent Mon 18 Jun 2007:

Larry,
If you are setting the ‘‘squish’’ at .040’’ you could go higher than
9:1 safely. Also, as Mr Olsen mentioned the mixture motion with the
hemispherical chambre is not very good, so you have the option of
making it better. A clue here would be to have a design that pushes
the gases to the spark plug area, so that the mixture ‘‘tumbles’’.
Also, try to make the piston top so that the spark plug sees all
the non-swished areas easily (i.e. no hidden pockets). This will
greatly reduce the octane requirement for your engine, so you could
bump the compression up even more. This is if you are interested in
more gains, as you are getting custom pistons made.

Regards

Don–
Petrarch
Los Gatos/CA, United States
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In reply to a message from Petrarch sent Wed 20 Jun 2007:

This is true, but I got the impression Larry was after a good rebuild with some blueprinting, not a full rework. Somebody in the UK (Cosworth? Rob Beere?) sells a set of asymmetric pistons with the domes fitting each hemi to correspond to the off-centre plug position but a) they’re not cheap & b) I think they aree only for 3.8 cars because of the bore centre issue on 4.2 cars. I suspect there’s a whole different order of work/price between shaving a standard type slug to adjust squish and creating a completely bespoke set of pistons. But I agree with your comments in a general sense.–
The original message included these comments:

making it better. A clue here would be to have a design that pushes
the gases to the spark plug area, so that the mixture ‘‘tumbles’’.
Also, try to make the piston top so that the spark plug sees all
the non-swished areas easily (i.e. no hidden pockets). This will
greatly reduce the octane requirement for your engine, so you could
bump the compression up even more. This is if you are interested in
more gains, as you are getting custom pistons made.


Peter Crespin 66E, 76 DD6 Coupe, 84 DD6, 85 XJS 5sp convert
Cambridge, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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