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MG MGB Technical - What is the Max over Bore size without Sleaving?

Gents,

Couple of questions.

1) Can all 3 Bearing and 5 Bearing blocks be bored out to the same max size?

2) Assuming you don't want to sleeve the block and don't use a stroker crank. How far can you go without risking cracking and overheating? Is it 1900cc or 1950cc or more. I forget the piston sizes in mm off the top. Perhaps someone can tell me.

Cheers
Mark.

Mark Hester

Mark,

it depends upon the block that is used and how skilled the machine shop personal is.
If you want to go away with the 1950 version, the bores have to be done a little offset.
Most engine tuners do only + 0.06 wihout sleevs and this will give you 1868. Boring up to 1950 can be a risk and for this reason most professionals use sleevs at this size. If you want to go further, a stroked crank will be necessary to exeed 2 litres) and a further amout of work on the block too.
You should plan your engine due to the kind of use you are after. If you post some of your ideas where fore you want to go to the limits of the bore here, experiances with such kind of setup can be given by others.

Ralph
Ralph

Mark
I'm flying by memory but Crankshaft Rebuilders (Melbourne - Ian Shugg) built my 2100cc B Series some 7 years ago and I think that the bores were taken out to 1950cc (offset as Ralph says) and the crank was stroked 6mm.
I will dig out the job sheet if you'd like me to confirm these things.
The car has been fabulous but took probably 10,000 miles to run in and get over early overheating problems - even with electric fan, aluminium radiator and such.
The big plus is the terrific torque - feels like a small V8 (I have a GT V8 also with the 3.5 litre motor).
Regards
Peter M
Peter M (member)

Mark;

If you want to max bore your block, then I would recommend that you have your machine shop perform ultrasonic testing (UT) of the cylinder wall thickness prior to any boring. The MGB engine blocks had some casting inconsistencies and it pays to check the wall thickness prior to boring.

I had my block bored out to 1924cc and the UT showed plenty of wall thickness so there were no worries about cutting through one of the cylinder walls.

Ron
Ron Kluwe

All,

It would be good to know how far people have bored blocks without sleeving them and how long they have lasted thus far.

Ron your comments about block inconsistencies and UT testing the block is the sort of thing I'm after.
If you went to 1924cc did your engine bore-er for want of a better term say you could go much beyond that?

FYI I don't need a massive amount of cc's as this block will have an mga twin cam head and ancillaries attached which should provide plenty of extra BHP.

Cheers
Mark.
Mark Hester

My 1979 1.8 was bored out .030 over from stock. So what does that give me now in CC's ??

cheers

Gary :>{D

79 mgb
gnhansen

Gary,

welcome in the '1840ccm class'.

Ralph
Ralph

Gary,

30 thou over gives 1834 cc

Mark,

I don't bore 3 bearing blocks to greater than +60 thou (1868cc)

5 bearing blocks can go out to +130 thou (1951cc) without sleeving or offsetting BUT you need to check the bores after boring as the mild steel straps that hold the sand cores together are embedded between 1 & 2 and 3 & 4.
Boring to +130 sometimes exposes these and they often have voids round them, so sleeving is a good idea.

Offset boring is not needed until you get to 2100cc.

Personally I think 1950cc is the practical limit - even then the engines are prone to blow by and oil burning due to wall flex. Using forged pistons with thinner rings alleviates this a little.

If you want more ccs then fit a V8!
Chris at Octarine Services

Many Thanks Chris.


From here:
http://www.mgbmga.com/tech/mgb11.htm

Std 1800cc 56.5cc 8.96:1
+010 1812cc 56.5cc 9.02:1
+020 1822cc 57.0cc 8.99:1
+030 1834cc 57.5cc 8.97:1
+040 1844cc 58.0cc 8.95:1
+050
+060 1868cc 58.5cc 8.98:1

83mm 1924cc 60.0cc 9.02:1
83.5mm 1948cc 61.0cc 8.98:1


Have you seen Bore Flex and Oil buring problems with 1924cc 83mm piston motors?

Cheers
Mark.
Mark Hester

Mark-
I have 83mm pistons in my engine. To prevent wall flexure that results in the oil burning and compression loss problems that often accompany big bore engines, I installed sleeves into the cylinders. Before any attempt to machine the bores is made, it must always be ascertained if any sleeves (liners) have been installed. This was occasionally done at the factory to salvage an engine block casting that would have been otherwise unusable due to problems with core shifting during the casting process that occasionally resulted in blocks with either off-center cylinders or cylinders of insufficient wall thickness. If a sleeve (liner) has been fitted, be aware that it cannot be rebored to accept an oversize piston. Instead, the block will have to be machined so that new sleeves (liners) can be press-fitted into all of the cylinders and original size pistons installed. It should be noted that the factory supplied oversize pistons only up to +.040” oversize due to variations in the thickness of the cylinder walls and problems with porosity that were due to the limitations of casting technology of the era. Bores beyond this diameter may require the fitting of sleeves (liners). There is an advantage to this approach. Sleeves (liners) can be made of special wear-resisting material that is likely to have a longer life than the original bore, as well as increased rigidity of the cylinder wall. Most sleeves (liners) have the advantage of being made of spun cast iron, which is of better quality than the ‘block-type’ grey cast iron, leading to a prolonged lifespan for the bore, as well as increased rigidity of the cylinder wall. Naturally, when fitting them the bores are opened out to a much greater extent than is used for a normal rebore. In view of the necessity of ensuring the correct interference-fit of the sleeve (liner) inside of the bore, plus the necessity of subsequent accuracy in the finishing-off of the bore of the liner, this method is more expensive than an ordinary “oversize” rebore. On balance, I would say that if the checkbook can stand it, sleeves (liners) are the best answer.
Steve S.

Steve,

Sleeves were also fitted to Gold Seal & Silver Seal engines to return the bore to standard size.

You CAN bore standard sleeves out to the first oversize - 20 thou - and fit oversize pistons.
Chris at Octarine Services

Steve, Others,

This twin cam engine will cost quite a few thousand, so I'm coming around to the idea of sleaves.

The only problem I see with sleaving the block is it relys on the machine shop doing the job correctly.

Steve, +60 pistons are easy to get off the shelf and +80 not that hard either.

Can anyone tell me what the choices are for the actual sleave it's self and who sells them, so I can do some research into the type of material I require.

Cheers
Mark.
Mark Hester

Liner manufacturers:

www.laystall.co.uk
www.westwood-trading.co.uk

Both with pedigree and high performance expereience

Colin
Colin Parkinson

Thanks Colin,

Some of these liners look quite fancy.

http://www.laystall.co.uk/layst7.htm

Do you need to select special rings to go with these linners?

Are there particular types that you have used in the part that you can recommend?

Cheers
Mark.
Mark Hester

Can anyone recommend any of these sleeves primarilary for racing?

Also how much do they cost and the cost to fit?

Cheers
Mark.
Mark Hester

Mark-
I contacted the two companies that Colin listed above and discovered that Laystall does not make liners for the BMC B Series engine except on a special order basis ($$$$!!). Westwood Trading, however, does make them on a regular production basis. Their part number for them is WCL 22. Cost is £25.90 each + VAT, and Carriage is £8.50 + VAT. County also makes liners for the B Series engine (County Part # CL1950). These have a wall thickness of .130”, are 6.060” long, and have an external diameter of 3.380”, (County Part # CL1950). These have a wall thickness of .130”, are 6.060” long, and have an external diameter of 3.380”, making them appropriate for engines in the 1868cc-1948cc catagory. I'm presently trying to get similar information from the Westwood Trading Company about the specifications of their liners.

Steve S.

Chris is spot on, I love the extra torque that 1950cc gives, but the block flex means I have had to give up on the PCV valve. My car was just bored without sleeves andf it worked fine. If I was doing this again for a daily driver I would not go beyond 1860cc.
Stan Best

Re Gold Seal engines and liners. When the Factory went to Qualcast for the blocks early 70 (18v) there were porosity problems which showed up on the assembly line. The blocks were rejected and put aside to be sleeved and returned to standard size, damage limitation exercise not special engineering!This info came from a retired machinist from BLMC.

I use liners in all our engines. The spun cast iron gives a better surface and you end up with more bhp and less oil consumption.

Peter
peter burgess

Peter-
Which company do you get your liners from?
Steve S.

Mark-
OK, here's the specification of the liners from Westwood Trading Company. They have a wall thickness of .105”, are 6.060” long, and have an external diameter of 3.265”, making them appropriate for engines in the +.20 to +.060 oversize category.
Steve S.

Hi Steve

We use County sleeves, they have special liners for std, +60 and for 1950 useage.

Peter
peter burgess

We've done a large number of blocks to 83.5mm (~1950cc) with only one failure.

For my own car, I've used 84mm (1972cc) reliably (2 engines since 1980)in all manner of competition, lots of revs, and as a daily runner for many years.

When the second 84mm engine finally gave up, I took it out to 84.5cc (1996cc) as a rebore. Went well for 4 years but developed a bore problem which may have been the oversize, but may have also been cooling system failure which overheated it.

In any of the above above, I've never had bore flex issues. However, one experimental block (for a customer who requested it) at 85mm, while it went very well, definitely had slight bore flex issues. The engine's still running quite well at last count, small oil consumption but the owner is happy.
Paul Walbran

Mark,

I am very keen to see how your conversion worked out. Curious to see about the redrilling of the studs, and head gasket.

Shareef
Shareef Hassan

I bought my B 2 and half years ago and at the time the engine had been completely redone and bored over .030 (I think) What CC would my 74 be now?
GG Ginty

GG-
+.030 gives 1833cc.
Steve S.

So it seems that 83 to 83.5 mm is about as much as you can go and still be reliable.

Any more than that, then you may as well stroke the crank to get the extra CC's.

Now I just need to find the correct dome'ed pistons for the twin cam head.

Cheers
Mark.
Mark Hester

Mark-
Contact Venolia @ venoliap@aol.com . They make pistons for the Twincam engine and should be able to provide a set for an 1800cc version. http://www.venolia.com/imports.html#MG
Steve S.

This thread was discussed between 30/10/2007 and 21/11/2007

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