15 replies to this topic

[Hpal]

I have the chance to buy a 1275 block which is at 1330now and will need to go to 1360, should I (can I) get it offset bored to even up the bore spacings between 2&3?  It is a 12YtaH (I think that's correct anyway) and has been described as a thin flange block. Can anyone tell me what exactly that refers to and is it a bad thing? What if I wanted to turbo it one day? Thanks guys.

[Spider]

The Flange that's referred to is the Sump Rails, where the Block bolts up to the Gearbox. The early blocks in all types were known as thin flange and then around 67 - 68 -ish, they made these flanges thicker.

 

For most engines, the flange thickness really doesn't matter, however possibly for something that's high reving with a fair bit of power output, a thick flange block maybe better. Nothing will break here, just be less prone to leaking oil.

 

The 12Y/Ta H Blocks came from the Morris 1100S Cars (the name is a misnomer, these are 1275 blocks). If you are contemplating a re-bore on it, if it can be off-set, then yes, that would be wise at the next bore, though, usually at +0.060" (which is what it'll be to get it to 1330) it may not be possible to off-set it. Usually if a block is to be off-set bored, it's done from the first bore.

 

The Block can of course, be fitted with Sleeves, which I gotta say, I prefer. It does of course add to the cost of the build, but the material in the Sleeves is better than the cast iron of the natural bore for most types of rings to run in.

[Cooperman]

I never have liked going beyond 1330 (+0.060") because once you offset bore, the next time a re-bore is needed it will need sleeves which may be more expensive.

At 1330 cc the best thing to do is to bore and sleeve back to 1275 cc. That way the block will last for a very long time. sleeves are excellent in terms of wear compared with standard cast iron.

[Spider]

I never have liked going beyond 1330 (+0.060") because once you offset bore, the next time a re-bore is needed it will need sleeves which may be more expensive.

At 1330 cc the best thing to do is to bore and sleeve back to 1275 cc. That way the block will last for a very long time. sleeves are excellent in terms of wear compared with standard cast iron.

 

I gotta say, I see this the same way. While doing the bigger bores can be done, they really don't give the extra power you might think. Like Cooperman, I 'top out' at +0.060" these days.

[Hpal]

Maybe if I use the block I'll just bore to 1360 and run it and worry about sleeving it in 20 years time after I wear it out. No big deal I guess. If I went again to 1380 does it definitely need offsetting to work or can you go non-offset 1380 but that the limit then resleeve after that?

[Cooperman]

A 1380 engine, or anything above +0.060" overbore, really must be offset bored. Cylinders 2 & 3 are already very close and if bored beyond +60 thou there will be problems.

Standard sleeves are not expensive when fitted to a +60 thou bore to get back to 1275 cc and those sleeves can, in turn, be bored further when needed.

I once had to 'sort' an engine which had been bored to 1380 cc by a so-called 'engine specialist'. It had not been offset and as soon as it started for the first time it threw oil out, then the head gasket gave up.

In the end it needed a complete replacement block because bores 2 & 3 were too close together to allow for offset boring and sleeving back. That was an expensive lesson.

Why didn't the owner take it back to the original 'specialist'? Because he had paid cash (no questions, no VAT) and they were not interested.

The only thing a 1380 gives is bar-room bragging rights (mine is bigger than yours!!). That is unless the car is for competition where every additional lb.ft. of torque, or bhp at the top end does matter.

What is interesting is that with a 998 block, if you fit a 1098 crankshaft and +100 thou pistons, you can get around 1180 cc without offset boring. 

[grizzler73]

liners if I were you, they can be re-bored at least once so its worth it, My race block has liners at 1275 (std) and it cost £400 all in.

Offsetting you can only do once. 

[Gilles1000]

Cooperman, if you fit a 1098 crank in a 998 block, would not the pistons sit proud of the top of the block, due to the stroke being bigger? Or is it fine with other (lower) pistons?

 

Sorry for the off-topic...

 

Gilles

 

A 1380 engine, or anything above +0.060" overbore, really must be offset bored. Cylinders 2 & 3 are already very close and if bored beyond +60 thou there will be problems.

Standard sleeves are not expensive when fitted to a +60 thou bore to get back to 1275 cc and those sleeves can, in turn, be bored further when needed.

I once had to 'sort' an engine which had been bored to 1380 cc by a so-called 'engine specialist'. It had not been offset and as soon as it started for the first time it threw oil out, then the head gasket gave up.

In the end it needed a complete replacement block because bores 2 & 3 were too close together to allow for offset boring and sleeving back. That was an expensive lesson.

Why didn't the owner take it back to the original 'specialist'? Because he had paid cash (no questions, no VAT) and they were not interested.

The only thing a 1380 gives is bar-room bragging rights (mine is bigger than yours!!). That is unless the car is for competition where every additional lb.ft. of torque, or bhp at the top end does matter.

What is interesting is that with a 998 block, if you fit a 1098 crankshaft and +100 thou pistons, you can get around 1180 cc without offset boring. 

[timmy850]

1098 engines have shorter pistons to match the increased stroke

Conrods are the same length

The only main difference in the short block is crank and pistons

[Cooperman]

With a 12g940 head an 1180 cc would go really well. Best carb would be either twin HS2 or a single HIF44, but a single HIF38 would work well.
You would get 1071 S power very cheaply.

[Gilles1000]

Wow, that would be quite a bit of a Frankenstein engine!!

[Northernpower]

Maybe if I use the block I'll just bore to 1360 and run it and worry about sleeving it in 20 years time after I wear it out. No big deal I guess. If I went again to 1380 does it definitely need offsetting to work or can you go non-offset 1380 but that the limit then resleeve after that?

If you are intent on a further bore there's no need to go to 1360, you could fit a set of Calverst 72.5 pistons https://www.calverst...perior-quality/ and settle for 1342cc  . If you did fit these I would suggest offset boring.

[Cooperman]

They look good.
The piston dish vol is only 6.5 cc, so the combustion chamber vol may need to be increased to suit.

[Northernpower]

They look good.
The piston dish vol is only 6.5 cc, so the combustion chamber vol may need to be increased to suit.

They are a very well made piston. I fitted them when I built my 7 port and I had to relieve them just slightly to give 9.75 to 1 compression.

[Hpal]

Very good idea, I could do a slight offset leaving enough on one side to clean the bore up and taking a bit more out of the other side.. If i were to re-sleeve I guess nomore than ? 0.020" ? more offset on the outer cylinders.

 

If you are intent on a further bore there's no need to go to 1360, you could fit a set of Calverst 72.5 pistons https://www.calverst...perior-quality/ and settle for 1342cc  . If you did fit these I would suggest offset boring.