Piston to bore clearance

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Cliffords
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Piston to bore clearance

Post by Cliffords »

Been doing some measuring whilst assessing my 912 2.2 LC engine and measured the pistons and bores now .
Does anyone have the original clearance specifications . At what point do they need new liners /pistons .

Appreciate it if anyone knows what is in spec and acceptable

Thanks

David

Pete Boole
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Re: Piston to bore clearance

Post by Pete Boole »

Clearance on a 912 LC is 0.005" to 0.006". The factory had "A" and "B" grade pistons and liners to choose from. Aftermarket liners are somewhat variable in their measurements - stick with the factory ones if you can.

Pete

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rbgosling
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Re: Piston to bore clearance

Post by rbgosling »

I have the later HC engine with nikasil-coated aluminium liners. I sent my liners off to be recoated, and they honed the bore to match my existing pistons. No idea what clearance they used, I'm afraid.
"Farmer" Richard

1990 Lotus Excel SE (Lilith)
2022 MG MG5 EV (not due to be a classic for quite a few years...)

Pete Boole
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Re: Piston to bore clearance

Post by Pete Boole »

Clearance for Nikasil liners is 0.002" to 0.003".

Pete

Cliffords
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Re: Piston to bore clearance

Post by Cliffords »

Here is a question that's been bothering me . My engine is in bits whilst I find a crank .
On many of the restoration pictures I see, the liners are clamped into the block during the rebuild , why is this ?

They are originally pressed into the block as a interference fit and , in a modern build a compound is added to help keep them in place . If the liner did move the engine would immediately be compromised as the water jacket would no longer be intact . If your liners move you have had it .

Mine have not moved yet and I have no clamps holding them in .

I am missing some knowledge here I expect .

Thanks

David

Pete Boole
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Re: Piston to bore clearance

Post by Pete Boole »

The liners are not an interference fit - they are a clearance fit. They just drop straight in. Earlier engines used Hylomar as the sealant which remains flexible hence the need to clamp the liners in place when removing the head. Hylomar was later replaced by a Loctite product (572) that sets hard - removing the head (in theory) will not disturb the liners. I use a liner clamp even when using the Loctite sealant - belt and braces!

If you aren't sure which sealant you have I'd clamp the liners down (actually I'd remove them regardless at the stage you're at!)

Pete

Cliffords
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Re: Piston to bore clearance

Post by Cliffords »

Thanks for the detail. Good to understand . I had assumed a press to get them out,I will have a go. It amazes me that gives a water tight seal under pressure.
Appreciate your help

David

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Re: Piston to bore clearance

Post by Pete Boole »

If they have been fitted in the past with the later sealant you will definitely need the right puller for the job - it's detailed in the workshop notes.

Pete

Cliffords
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Re: Piston to bore clearance

Post by Cliffords »

Thanks Pete. I still have not managed to get a copy of the workshop notes.
David

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rbgosling
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Re: Piston to bore clearance

Post by rbgosling »

When I stripped my engine ('90 SE) I was lucky to be able to borrow a liner puller while I was at the NEC Resto show. However they came out quite easily, and I probably could have got them out without the puller. But that was just my engine, it might not always go that way!

I would definitely use liner clamps once you have them seated back in place, the chances are just too high of knocking them slightly and breaking the seal during piston insertion, particularly when rotating the crank and moving the pistons up and down without the head on.
"Farmer" Richard

1990 Lotus Excel SE (Lilith)
2022 MG MG5 EV (not due to be a classic for quite a few years...)

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