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Discussion Starter #1 (Edited)
Didn't see any LK5 piston specs mentioned anywhere in the LK5 engine swap thread from which I copied these posts and didn't really expect it in an 'engine-swap' forum. So, let me ask straight out if anyone knows what the pin diameter and combustion height of the stock 93mm LK5 pistons are?

I've looked around the net fairly extensively for these two specific LK5 piston specs, but have come up dry so far. My interest is for possibly using them milled flat on top with valve reliefs cut in a standard bore 1.9 CIH block with a 2.2 crank and 1.9 forged rods, if dimensions are close.

Want to avoid boring block, if at all possible. Already know it's a real bitch finding 93mm-bore pistons of any kind, other than stock and standard oversize cast 1.9 pistons! . . . have been looking for a long time already.
 

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also noticed they are domed .095".. Kind of cool the motor is really close to the Opel dimensionally internally too.
 

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Discussion Starter #6
Hmmm, is that . . .

The compression height 05 LK5 vin 8 is........1.101
as per http://www.kb-silvolite.com/assets/09_silvolite_catalog.pdf
So with a 5.557" (141mm) rod you're all set...:banghead:
. . . the standard 1.9 rod length, Bob, or one of your alternate, modified 'standard' rods from another make? . . . Chevy, Ford, Volvo?

Two things are really intriguing about this piston for my particular use . . . Hypereutectic type with coated skirts . . .
 

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. . . the standard 1.9 rod length, Bob, or one of your alternate, modified 'standard' rods from another make? . . . Chevy, Ford, Volvo?
Total sarcasm. I don't know of any rods that length that will work. Opel used 128 mm rods (1.5 through 2.2 CIH engines) and 134 mm rods (2.4 CIH engines).

The 2.2 Opel compression height is 1.619", which is quite a bit different from 1.101"!
 

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Discussion Starter #8
Some further thoughts . . .

The compression height 05 LK5 vin 8 is........1.101
as per http://www.kb-silvolite.com/assets/09_silvolite_catalog.pdf
So with a 5.557" rod you're all set...:banghead:
also noticed they are domed .095".. Kind of cool the motor is really close to the Opel dimensionally internally too.
. . . after reviewing several of Bob's long ago 'engine-build' e-mails to me. How about using these LK5 pistons with Bob's suggested Dodge Neon 2.0, 139mm length (+11mm) rod replacements then? A bit of additional rod machining is required, granted, but they're very close dimensionally to Opel's stock, forged 128mm CIH rods. They are, however, much stronger and with a much better rod ratio too, 1.79 vs. 1.65 for the 2.2 stroke!

So, 208mm/8.2" (CIH-DH) - [139mm/5.472" (Neon-RL) + 38.75mm/1.526" (½-2.2S)] = 30.25mm/1.191" (CH) . . . :ponder: . . . that's only 2.3mm/.090" greater (down in the bore) than the LK5 93mm piston's 28mm/1.101" CH!

BUT, the LK5 piston has a 2.4mm/.095" dome, so the dome top is basically flush with the deck . . . and you could machine the necessary CIH valve reliefs directly in the dome top! In a nutshell, lighter Hypereutectic pistons, lighter crank and much better rod ratio . . . what's not to like!!

Comments?!! . . . Bob?
 

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I'd be worried about the quench area with the piston that far down in the hole.

We're talking about combustion inefficiencies here, so you might end up with an engine that rattles with 'normal' ignition timing settings, spews out excessive emissions with bad fuel economy and definitely leaves some power on the table.

It's hard enough to get a wedge chamber to be efficient with the piston flush with the deck!
 

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Discussion Starter #10
Kinda thought that . . .

I'd be worried about the quench area with the piston that far down in the hole.

We're talking about combustion inefficiencies here, so you might end up with an engine that rattles with 'normal' ignition timing settings, spews out excessive emissions with bad fuel economy and definitely leaves some power on the table.

It's hard enough to get a wedge chamber to be efficient with the piston flush with the deck!
. . . but thanks anyway, Bob.
 

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Was pointed here from the thread I started in 'Opel Engine Performance Modifications' on the same topic, am just starting out this route myself...hadn't read this section of the forum at all.

How about these:
Piston Search

Flat top, 93mm bore, 41.65mm compression height, only snag is that pin diameter is 24mm. From answers on the thread I started, the opinion seemed to be that it should be possible to open the small end on the opel rods by 1mm?
 

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Discussion Starter #13 (Edited)
Pinto 93mm piston specs . . .

Was pointed here from the thread I started in 'Opel Engine Performance Modifications' on the same topic, am just starting out this route myself...hadn't read this section of the forum at all.

How about these:
Piston Search

Flat top, 93mm bore, 41.65mm compression height, only snag is that pin diameter is 24mm. From answers on the thread I started, the opinion seemed to be that it should be possible to open the small end on the Opel rods by 1mm?
Yep, piece of cake. There are other dangers to beware of . . .


. . . also shows piston crown thickness (PCT) of just 6.4mm/.25", which means that crown thickness must be milled by the 0.55mm/.022" greater piston CH of this piston before the ~3.5mm/.140" deep 23〫angled valve reliefs can be cut!

Synopsis math: 6.4mm/.25" (PCT) − 0.55mm/.022" (CH diff.) = 5.85mm/.23" (PCT) − ~3.5mm/.140" CIH valve reliefs = 2.35mm/.093" (PCT) at deepest part of valve reliefs . . . not good, even with stronger forged pistons!

. . . better to start with stock Opel 1.9 93mm flat-tops at double the PCT, 12.7mm/.50", methinks!
 

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Yes..I see what you mean. Thanks for pointing that out! To be honest thats good news, since I know the pistons in the shortblock are brand new, so buying another new set would be galling..!

One other thing, on my original thread,
http://www.opelgt.com/forums/opel-engine-performance-modifications/26424-best-way-forward-new-1-9-shortblock-2-2-crank.html
where I asked if it would be OK to machine the standard pistons, I was told it wouldn't be? "No, you cannot cut the flat top pistons and then cut the valve reliefs, it will make the top of the piston under the valve relief too thin and result in failure of the piston"...but maybe I had phrased my question badly, and LLoyd misunderstood...Your maths don't lie!

Carrying on with your numbers, but for the standard pistons:
12mm/.5" (PCT) − 3.85mm/.152" (CH diff.) = 8.15mm/.321" (PCT) − ~3.5mm/.140" CIH valve reliefs = 4.65mm/.183" (PCT) at deepest part of valve reliefs...still safe?
 

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Discussion Starter #15 (Edited)
Yes, but a half inch PCT . . .

Yes..I see what you mean. Thanks for pointing that out! To be honest that's good news, since I know the pistons in the short-block are brand new, so buying another new set would be galling..!

One other thing, on my original thread,
http://www.opelgt.com/forums/opel-engine-performance-modifications/26424-best-way-forward-new-1-9-shortblock-2-2-crank.html
where I asked if it would be OK to machine the standard pistons, I was told it wouldn't be? "No, you cannot cut the flat top pistons and then cut the valve reliefs, it will make the top of the piston under the valve relief too thin and result in failure of the piston"...but maybe I had phrased my question badly, and LLoyd misunderstood...Your maths don't lie!

Carrying on with your numbers, but for the standard pistons:
12mm/.5" (PCT) − 3.85mm/.152" (CH diff.) = 8.15mm/.321" (PCT) − ~3.5mm/.140" CIH valve reliefs = 4.65mm/.183" (PCT) at deepest part of valve reliefs...still safe?
. . . is actually 12.7mm! . . . and I would machine the Opel 'flat-top' PCT only 3.55mm/.140" because CIH pistons are typically installed .005"-.008" 'down in the hole/below deck' at the factory.

I know 1mm total difference doesn't sound like much, but it results in a 'valve reliefs' PCT of 5.65mm/.223" . . . much closer to the original 6.35mm/.25" PCT of the 93mm Ford Pinto piston suggested!
 

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My interest is for possibly using them milled flat on top with valve reliefs cut in a standard bore 1.9 CIH block with a 2.2 crank and 1.9 forged rods, if dimensions are close.

Want to avoid boring block, if at all possible. Already know it's a real bitch finding 93mm-bore pistons of any kind, other than stock and standard oversize cast 1.9 pistons! . . . have been looking for a long time already.
Otto, I know you're hellbent on not boring your block oversized. However, if you are looking for a solution that requires only modest machine work and utilizes off-the-shelf components I have a suggestion. It should also be virtually bulletproof under most conditions (hypereutectic pistons are not tolerant of detonation!).

*Use your 2.2 crankshaft
*Use a 1.9 block
*Use Keith Black KB153 305 Chevy pistons for 6" rods - 1.261" compression height - use std bore 3.736" (94.8944 mm). These are hypereutectic pistons.
*Use Crower Sportsman rods, 5.4" long #SP93232B-4. These have to be narrowed .013" on the big ends to fit the Opel journals, but can use the stock Ford 2.3 bearings. The pin end needs enlarging from .912" to .927", and use full-floating pins.
*Pistons will be .003" higher in the bore than stock 2.2 pistons.
*Rod ratio will be 1.7699, which is just about the perfect compromise between high rpm power and torque.
*Pistons are 179 grams lighter (each). Pins are 20 grams lighter each.
*Displacement will be 2192 cc's.

Just a thought.
Bob
 

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Discussion Starter #17
Hmm . . .

Otto, I know you're hellbent on not boring your block oversized. However, if you are looking for a solution that requires only modest machine work and utilizes off-the-shelf components I have a suggestion. It should also be virtually bulletproof under most conditions (hypereutectic pistons are not tolerant of detonation!).

*Use your 2.2 crankshaft
*Use a 1.9 block
*Use Keith Black KB153 305 Chevy pistons for 6" rods - 1.261" compression height - use std bore 3.736" (94.8944 mm). These are hypereutectic pistons.
*Use Crower Sportsman rods, 5.4" long #SP93232B-4. These have to be narrowed .013" on the big ends to fit the Opel journals, but can use the stock Ford 2.3 bearings. The pin end needs enlarging from .912" to .927", and use full-floating pins.
*Pistons will be .003" higher in the bore than stock 2.2 pistons.
*Rod ratio will be 1.7699, which is just about the perfect compromise between high rpm power and torque.
*Pistons are 179 grams lighter (each). Pins are 20 grams lighter each.
*Displacement will be 2192 cc's.

Just a thought.
Bob
. . . sounds very interesting, Bob . . . does require block bore, but that does have some positive offsets for valve shrouding, so . . .

Couple of questions though . . . come on, you knew there were going to be some! . . . anywhere you can buy just a half-set, four, of those KB pistons? . . . any problems with the small C-to-C valve spacing differences between Chevy (1.863") and Opel (1.806")? . . . and are those pistons available with both 'IE' and 'EI' valve reliefs or are they 'same size'?
 

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. . . sounds very interesting, Bob . . . does require block bore, but that does have some positive offsets for valve shrouding, so . . .

Couple of questions though . . . come on, you knew there were going to be some! . . . anywhere you can buy just a half-set, four, of those KB pistons?
You can buy them individually or a full set. Summit carries them.

. . . any problems with the small C-to-C valve spacing differences between Chevy (1.863") and Opel (1.806")?
Shouldn't be an issue with most valve sizes and most street cams.

. . . and are those pistons available with both 'IE' and 'EI' valve reliefs or are they 'same size'?
They are available as 'lefts' and 'rights', yes.

http://www.summitracing.com/parts/UEM-SKB153R-STD/
http://www.summitracing.com/parts/UEM-SKB153L-STD/
 

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. . . sounds very interesting, Bob . . . does require block bore, but that does have some positive offsets for valve shrouding, so . . .
As always I'm eager to learn so I can't help asking, why do you want to avoid boring your block ?
 

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Discussion Starter #20
One word . . .

as always i'm eager to learn so i can't help asking, why do you want to avoid boring your block ?
. . . Cheap!
 
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