Lotus Elan

REBORING LINERED BLOCK

PostPost by: normanjsmith » Sat Jun 15, 2019 11:20 am

I've had a spare twin cam block under my workbench for 35 years. It is well worn and has a casting number 701M6015A with LB stamped on the front face. It was linered from new in all cylinders. Is reboring advisable / possible because the wall thickness of the liner appears to be about 1mm?

Norm
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PostPost by: Hawksfield » Sat Jun 15, 2019 11:47 pm

Hi
My block is linered and had std pistons, I have had it bored to 0.20 without problems
I am pretty sure it was original and is an LB block
Regards

John

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PostPost by: avro » Sun Jun 16, 2019 12:08 am

Hello Norm

Quite where l got the information from l can’t remember, perhaps from a more experienced machinist all those years ago or from something l had read, but my understanding is that a factory linered cylinder block should only be rebored to a maximum of +20.
Coincidentally l have just rebored a linered block this week ( one of many over the years). Your post has just prompted me to go and measure the actual liner thickness . At the bottom of the cylinder liner at the location of the conrod relief they don’t always grind the liner fully to match the original casting and that has allowed me to accurately measure the liner thickness. With a +20 rebore the liner wall thickness is .050” inches.
If your block is badly worn it may not be possible to clear the wear ridge with a straight rebore. However the wear ridge is never equal throughout the full circumference of the bore and it is possible to very slightly offset the boring bar toward the worst area of wear to achieve a successful result. Have a word with your local experienced machinist.

Nick
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PostPost by: Elan45 » Sun Jun 16, 2019 6:56 pm

You could have the old liners removed and new ones pressed in place. Make sure the liners have some way to be trapped, such as a ridge at the bottom of each cylinder or a step/ flange on the outside top of the sleeve which locates into a step in the top of the raw cylinder in the block. I know at least one race engine builder who says the sleeve material is so much better than the original block material that he bore and sleeves all his best engines.

Roger
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PostPost by: normanjsmith » Sun Jun 16, 2019 11:20 pm

John, Nick and Roger - thanks for your replies. It is reassuring to know it can be rebored without the expense of fitting new liners.I am confident a .020" rebore will clean it up because the wear, while obvious, is not excessive.

I wonder what percentage were linered from new - I have 3 twin cams and two of them are linered.

Norm
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