1996 TRW/Manley 49cc Dome Pistons - Need technical info please

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patrickonb
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1996 TRW/Manley 49cc Dome Pistons - Need technical info please

Post by patrickonb »

Hi Folks,

I've got a set of these pistons from 1996, they're in a Manley box, but as you can see in the photos below,
they must have been made by TRW for Manley.

These are for a BBC, using a 4.280 bore, and use 1/16" rings.

What I need to know is, what kind of bore clearance do I need with these? I've done a lot of searching, but can't
find any catalog info on these, so not sure what the manufacturer recommended for these. I believe these are
old enough, that fitting these to your bore was a thing back then, correct?

I supplied some photos below:

Thanks, Patrick

P.S. These will be used in a bracket engine, they will not be used on the street. Thanks.

Image
Image
Image
Image
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Re: 1996 TRW/Manley 49cc Dome Pistons - Need technical info please

Post by BillK »

Have you called Manley ? They have always been helpful in the past. (732) 905-3366

I have a somewhat old Manley catalog at the shop but I am not sure if they showed clearances in their catalogs.
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Re: 1996 TRW/Manley 49cc Dome Pistons - Need technical info please

Post by af2 »

patrickonb wrote: Thu Jul 28, 2022 1:30 am Hi Folks,

I've got a set of these pistons from 1996, they're in a Manley box, but as you can see in the photos below,
they must have been made by TRW for Manley.

These are for a BBC, using a 4.280 bore, and use 1/16" rings.

What I need to know is, what kind of bore clearance do I need with these? I've done a lot of searching, but can't
find any catalog info on these, so not sure what the manufacturer recommended for these. I believe these are
old enough, that fitting these to your bore was a thing back then, correct?

I supplied some photos below:

Thanks, Patrick

P.S. These will be used in a bracket engine, they will not be used on the street. Thanks.

Image
Image
Image
Image
Looks like the old 2618 castings. I see them at .004 to as far as .008 that a friend was running.
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Re: 1996 TRW/Manley 49cc Dome Pistons - Need technical info please

Post by af2 »

patrickonb wrote: Thu Jul 28, 2022 1:30 am Hi Folks,

I believe these are
old enough, that fitting these to your bore was a thing back then, correct?

Still is!
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Re: 1996 TRW/Manley 49cc Dome Pistons - Need technical info please

Post by Tom68 »

patrickonb wrote: Thu Jul 28, 2022 1:30 am Hi Folks,

I've got a set of these pistons from 1996, they're in a Manley box, but as you can see in the photos below,
they must have been made by TRW for Manley.

These are for a BBC, using a 4.280 bore, and use 1/16" rings.

What I need to know is, what kind of bore clearance do I need with these? I've done a lot of searching, but can't
find any catalog info on these, so not sure what the manufacturer recommended for these. I believe these are
old enough, that fitting these to your bore was a thing back then, correct?

I supplied some photos below:

Thanks, Patrick

P.S. These will be used in a bracket engine, they will not be used on the street. Thanks.

Image
Image
Image
Image
Measure them, they'll be 4.280" minus clearance, i.e around 4.274"
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Re: 1996 TRW/Manley 49cc Dome Pistons - Need technical info please

Post by In-Tech »

Hiya,
.006"-.008" on a casual, .008"-.010" on a for real, high hp drag or endurance application. Lean towards the high of either application if cold noise doesn't matter. Black death skirt lives matter :lol:
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Re: 1996 TRW/Manley 49cc Dome Pistons - Need technical info please

Post by patrickonb »

Thanks everyone for your responses!

Why I didn't think about calling them is beyond me! SMH

Thanks,
Patrick
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Re: 1996 TRW/Manley 49cc Dome Pistons - Need technical info please

Post by patrickonb »

Just in case anyone else has been interested in the outcome of this post, Manley informed me that these
are a MS75 11% silicone aluminum. 49cc dome. Requires a .006" clearance. Their part number on them
was 49653. 1.395 compression height, using a 6.385 rod.

Patrick
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Re: 1996 TRW/Manley 49cc Dome Pistons - Need technical info please

Post by Dan Timberlake »

Did they mention if the piston measuring point was at the wrist pin CL, the tip of the skirt, or some where else ?

I'd still measure the piston and compare to nominal "for fun."

Looks like the wavy skirt profile , which was fairly scuff resistant.

The drilled oil return holes in the oil ring groove makes for a strong piston, but the skirt is stiff (requiring generically extra fitted clearance) compared to ones with slotted oil returns .
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Re: 1996 TRW/Manley 49cc Dome Pistons - Need technical info please

Post by Dave Koehler »

I used those in a past life. They work fine. Your final bore size can be 4.280 to 4.281 depending on desired clearance.
Check piston dome to head clearance if you have a printed deck height and naturally piston to valve clearance.
Larger than oem intake valves can catch the lip of the intake pocket. So....trust but verify.
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Re: 1996 TRW/Manley 49cc Dome Pistons - Need technical info please

Post by rgalajda »

Dave Koehler wrote: Mon Aug 01, 2022 3:55 pm I used those in a past life. They work fine. Your final bore size can be 4.280 to 4.281 depending on desired clearance.
Check piston to head clearance if you have a printed deck height and naturally piston to valve clearance.
Larger than oem intake valves can catch the lip of the intake pocket. So....trust but verify.
What is a " printed deck height " ?
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Re: 1996 TRW/Manley 49cc Dome Pistons - Need technical info please

Post by rgalajda »

Correct me if I'm wrong.

So these are 454BBC pistons for a 6.385 rod as opposed to OEM 6.135 rod. Difference being .250"

Piston C/H 1.395 as opposed to OEM 1.645". Difference being .250"

Dome 49cc or .650" approximately giving a 12:1 compression ( approx ) with a 118cc open chamber head.

MS75 11% silicone aluminum would be similar to 4032 Alloy . This would need about .001" less clearance than 2618 Alloy for a "Street Naturally Aspirated application".

Usually "Clearance has been built into the piston" Wouldn't .035 to .045" be typical ? "Street Naturally Aspirated application or .005 to .007" for " Drag Gasoline " application
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Re: 1996 TRW/Manley 49cc Dome Pistons - Need technical info please

Post by Dan Timberlake »

enlarging or deepening the intake pocket can break into the top ring groove on some of those BBC pistons.
Some guys ran them with some success even with the accidental gas port, but I can't see the thin edge of the "gas port" or the piston ring enjoying being bathed in fire for long.
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