Lotus Elan

Bore size

PostPost by: wobblyweb » Thu Jan 26, 2023 4:25 pm

I am having problems with my engine, water is leaking into the bore. I thought it was caused by the head but on stripping down I have found the following :-
DSC00838.JPG and

DSC00839.JPG and


Looking at second hand blocks the bores are listed as 83.5mm etc . Mine is bored to +40thou
What will that equate to in mm ?
If I can have the blocked sleeved would it be stupid to bore it out to 40 thou and use my pistons.

Anyone have a block for sale?

Thank you
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PostPost by: Barney » Thu Jan 26, 2023 5:27 pm

A quick google gave me this
40thou.JPG and
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PostPost by: wobblyweb » Thu Jan 26, 2023 5:47 pm

Thank you, not written very well. I can do the conversion for +40 but what will the total bore size be ie 83.5mm
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PostPost by: Craven » Thu Jan 26, 2023 8:06 pm

Twincam standard bores are in imperial inches 3.25” so + 40 pistons are 3.25 + 0.040 = 3.290 inches.
Covert to metric mm = 3.290 X 25.4 gives 83.566 mm
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PostPost by: 512BB » Thu Jan 26, 2023 11:58 pm

And if you do not understand the above calculations, your piston size at .040" oversize is 83.5mm approx. In other words, your block has reached its maximum safe oversize. Some have, and do go further, but foolishly in my opinion, if you want to drive with a bit of peace of mind that your bores are not going to split.

So your only option with that block is to have it sleeved back to standard, and to buy new pistons and rings. It would be daft to have it sleeved and then taken out to +40 again, just to use your existing pistons, as you would be wasting 200k odd miles of wear on the bores, and you would have to buy new piston rings anyway, and that is if your pistons are serviceable.

Choose your engineers of choice very carefully when deciding who will do the resleeving. And if you go ahead with that, take some good pictures of the top of the block and from inside, after the job has been completed, and post them please, as this is a very interesting topic, to me at least.

I will post a picture later, if I can find it, of a block that had been sleeved from the Factory.

Leslie
Last edited by 512BB on Fri Jan 27, 2023 8:26 am, edited 2 times in total.
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PostPost by: snowyelan » Fri Jan 27, 2023 1:06 am

Excuse the interruption, genuine questions I don't think I have seen answered before.

For those with experience, I have a couple questions.

1. Is it acceptable to sleeve a block with cracked bores?
2. What is the typical OD of sleeves?
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PostPost by: rgh0 » Fri Jan 27, 2023 11:39 am

Most blocks can be bored to 83.5 but many of these most require offset boring to maintain an acceptable block wall thickness. A crack like shown probably has a wall thickness less than 2.5mm / 0.1 inch at the crack because it was not offset bored

Sleeving a cracked bore is generally not a good idea. You need at least 2mm left in the bore wall and at least 1.5 mm left in the sleeve wall and whats left in the bore wall casting needs to be sound to support the sleeve and the cracked bore does not do this. This just my opinion and I am sure others may differ So if aiming for a 82.5 mm standard bore, the block needs to be bored to 85.5mm at which point you may have none or little block casting bore wall left especially in the area where its cracked which you know is thin already at an 83.5 mm bore. If you offset bore for the sleeve you may be able to get adequate wall thickness but each job needs assessment on a case by case basis by someone who does a complete bore wall thickness survey first and knows how to assess the data.

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PostPost by: wobblyweb » Sat Jan 28, 2023 2:45 pm

DSC00843.JPG and

Tried some dye penetrant on the marks on the bore but nothing showed up.
I think I will need to strip the block and have the head and block pressure tested
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PostPost by: alan.barker » Sat Jan 28, 2023 3:11 pm

Hi wobblyweb,
If you decide to get the block step sleeved i think the sleeves that can be used are merc 190D or something like that . Shortened in length i think. Ref David Vizard book.
Standard original bore pistons can be found very cheap. If normal driving standard pistons are ok if not thrashing engine.
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PostPost by: Craven » Sat Jan 28, 2023 4:11 pm

These people will make liners to order as well.
https://www.ebay.co.uk/itm/373654343746 ... SwO65g9VKj
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PostPost by: 2cams70 » Sun Jan 29, 2023 2:40 am

Those marks on the bore are likely just rust marks caused by coolant leaking into the cylinders from a faulty head gasket or head. At 83.5mm it’s highly unlikely to have cracked a cylinder. Once you have it dismantled have the block sonically tested for thickness. You may be able to take it out to 0.060” OS.
Moral of the story. If you have a leaking head gasket attend to it fast. When first noticed run the engine until warm and then drain the coolant so you don’t risk this happening.
QED sell both thick and thin wall cylinder liners for this block. The thin wall liners require the bore to be taken out to around 85.5mm prior to pressing them in. Thick wall liners can be used to salvage something more seriously damaged. Many racing engines running with liners without issue. The liner material is generally harder than the native cast iron the block is made from so you can get increased life between rebores.
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PostPost by: Donels » Sun Jan 29, 2023 3:32 pm

What size head gasket was used? If it’s standard size then the fire ring has probably been burned allowing the leak. Before fitting new liners check the cheap and easy stuff.
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PostPost by: wobblyweb » Wed Feb 01, 2023 10:09 am

Head has gone to be pressure tested, first response from the builder was that it could do with a skim as there were gasket marks on the face that could allow water past.

Thank you all for responses and help, I will let you know of the outcome of the pressure test.
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PostPost by: rgh0 » Wed Feb 01, 2023 10:28 am

You should get it hardness tested as well as pressure tested. Gasket marks from the fire ring that need the head facing is a possible indication of a soft head.

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