Jump to content

BMC 2.2 and 2.5 crankshafts the same?


jnrhacksaw

Featured Posts

1 hour ago, Mike the Boilerman said:

I'd agree. Back in the day BMC were in the habit of increasing their engine capacities by forging longer stroke cranks rather than casting different blocks.

?????

As Richard says the difference in capacity od a 2.2 and a 2.5 BMC comes from a bore difference not a stroke difference.

1.5 and 1.8 is the same - same stroke but bore size increased.

Doesn't this also apply to things like H series Listers?

HA and HR have same stroke I think, but HR has increased bore size?

Link to comment
Share on other sites

4 minutes ago, alan_fincher said:

?????

As Richard says the difference in capacity od a 2.2 and a 2.5 BMC comes from a bore difference not a stroke difference.

1.5 and 1.8 is the same - same stroke but bore size increased.

Doesn't this also apply to things like H series Listers?

HA and HR have same stroke I think, but HR has increased bore size?

Yes, blocks are easily and cheaply bored out (if designed that way), but producing different throw crankshafts is more expensive. 

Link to comment
Share on other sites

4 minutes ago, alan_fincher said:

?????

As Richard says the difference in capacity od a 2.2 and a 2.5 BMC comes from a bore difference not a stroke difference.

1.5 and 1.8 is the same - same stroke but bore size increased.

Doesn't this also apply to things like H series Listers?

HA and HR have same stroke I think, but HR has increased bore size?

If you have a background in Fords, you'll find the 1.1 and 1.3 crossflow engines had the same bore but a different stroke. That way you can make a family of engines with a lot of common parts - only the crankshaft and rods are different

The H series variation is because of engine development

Richard

1 minute ago, cuthound said:

Yes, blocks are easily and cheaply bored out (if designed that way), but producing different throw crankshafts is more expensive. 

Not really true. You have to have enough (i.e. too much) metal in the block, or waterways that can be shrunk down. Otherwise, you need a redesigned block, head, pistons, valves...

Richard

Link to comment
Share on other sites

One of the reasons I have heard regularly quoted that the 1.8 BMCs are more prone to cylinder head gasket failure than the 1.5s is that the increase in bore results in not enough gasket between adjacent cylinders.  I was surprised when our 1.8 was so diagnosed just how small the separation is on some, (but not all) of them.

Link to comment
Share on other sites

Clearly I was talking rubbish. 

I was thinking of the Mini Coper 'S', a car about which I know (or knew!) quite a lot.

The first 970cc Cooper 'S' engines were upgraded to 1,071cc by fitting a longer stroke crank, then a longer stroke crank still was used to increase the capacity again to 1,275cc IIRC. I thought BMC did this routinely when they increased engine capacity but it appears not. 

Link to comment
Share on other sites

1 hour ago, Mike the Boilerman said:

Clearly I was talking rubbish. 

I was thinking of the Mini Coper 'S', a car about which I know (or knew!) quite a lot.

The first 970cc Cooper 'S' engines were upgraded to 1,071cc by fitting a longer stroke crank, then a longer stroke crank still was used to increase the capacity again to 1,275cc IIRC. I thought BMC did this routinely when they increased engine capacity but it appears not. 

You aren't quite correct on this.

The first Cooper S was the 1071 model, which, with a 40 thou overbore went to 1098cc, just right for the then racing class of up to 1100cc. 

Then then motorsport governing body replaced the upto 1100cc class with two classes, up to 1000cc and up to 1300cc (capacity classes which still exist today incidentally). BMC's response was to drop the 1071cc engine and replace it with two new ones, the 970cc of 1275cc respectively. When over bored by 40 thou, they became 999cc and 1293cc respectively.

You are correct that the original capacity changes came from different crankshafto though, nitrided for the 970cc and 1275cc engines.

Once they had built the number of 970's needed for homologation (official type approval for racing), they dropped the 970cc Cooper S as no one except those intending to race or rally it bought them.

All are worth serious money in good condition these days, (£25k to £50k). 

I had a 970cc S which I rallied in 1973 and 1974, then sold for £500. Wish I had kept it, they are the rarest of all Cooper S's.

Link to comment
Share on other sites

I'm looking for a crankshaft for a 2.5 mine has spun the middle main bearing. The one below is listed for a LD van had a 2.2 fitted

http://www.ebay.co.uk/itm/Genuine-BMC-Crankshaft-with-Bearings-Morris-Id-Van-Part-Number-28G80-3H-EB/131841165166?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649

However on closer inspection I'm not sure its the same as mine, anyone know the parts numbers and what it may be for?

Link to comment
Share on other sites

7 hours ago, RLWP said:

If you have a background in Fords, you'll find the 1.1 and 1.3 crossflow engines had the same bore but a different stroke. That way you can make a family of engines with a lot of common parts - only the crankshaft and rods are different

The H series variation is because of engine development

Richard

Not really true. You have to have enough (i.e. too much) metal in the block, or waterways that can be shrunk down. Otherwise, you need a redesigned block, head, pistons, valves...

Richard

the rover 3500 v8 was a good example of this

3.5 was fine
3.9 was generally good (but did used to go through head gaskets a bit quicker)
4.2 was prone to failure

edit: to add..
I ran a rangerover (3.9) for 15 years and every 3 years without fail it would start leaking between cylinder 1 and the cooling system (never mixed oil and water, just pressurised the water)
so every 3 years that sides head gasket got replaced (the other side never had a problem)

Edited by Jess--
Link to comment
Share on other sites

My father ran a fleet of fx 4 taxis in the late 60`s through the 70`s with the bmc 2.2 engines, clapped out ex london rejects they were, held together with chewing gum, spit and hope. These all had the 3 main bearing cranks, being 2.2s . in 1977, queens silver jubilee year, he 're named it jubilee taxis, and splashed out on a brand new fx4, mnc 385p. The only new vehicle he ever had. This had the new 2.5 engine, an alternator, not a dynamo, and those funny little heater plugs in parallel, instead of the 2 volt series things that never seemed to work. It was an improved & updated replacement for the 2.2, with 5  main bearings. I'm wondering now if there was an early version of the 2.5  with a 3 bearing crank, later ones having 5? I was talking to mate of mine today who had a taxi repair business around this time, he remembers bmc 2.5`s having a 5 main bearing crank too. I put one in a series 2 landrover once, was a popular conversion at the time. 

  • Greenie 1
Link to comment
Share on other sites

9 minutes ago, crossley said:

My father ran a fleet of fx 4 taxis in the late 60`s through the 70`s with the bmc 2.2 engines, clapped out ex london rejects they were, held together with chewing gum, spit and hope. These all had the 3 main bearing cranks, being 2.2s . in 1977, queens silver jubilee year, he 're named it jubilee taxis, and splashed out on a brand new fx4, mnc 385p. The only new vehicle he ever had. This had the new 2.5 engine, an alternator, not a dynamo, and those funny little heater plugs in parallel, instead of the 2 volt series things that never seemed to work. It was an improved & updated replacement for the 2.2, with 5  main bearings. I'm wondering now if there was an early version of the 2.5  with a 3 bearing crank, later ones having 5? I was talking to mate of mine today who had a taxi repair business around this time, he remembers bmc 2.5`s having a 5 main bearing crank too. I put one in a series 2 landrover once, was a popular conversion at the time. 

The Early MGB's had a 3 Bearing Crank in the 1.8 Petrol Engine,after   65 ish they had a 5 Bearing one

My Boat,built in 1996,Has had a BMC 2.5(1977 Vintage) since new.

Link to comment
Share on other sites

2 minutes ago, cereal tiller said:

The Early MGB's had a 3 Bearing Crank in the 1.8 Petrol Engine,after   65 ish they had a 5 Bearing one

My Boat,built in 1996,Has had a BMC 2.5(1977 Vintage) since new.

 

2 minutes ago, cereal tiller said:

The Early MGB's had a 3 Bearing Crank in the 1.8 Petrol Engine,after   65 ish they had a 5 Bearing one

My Boat,built in 1996,Has had a BMC 2.5(1977 Vintage) since new.

Yes, the early 1489cc MGB had the 3 bearing crank.

Link to comment
Share on other sites

On 7/24/2017 at 19:06, crossley said:

My father ran a fleet of fx 4 taxis in the late 60`s through the 70`s with the bmc 2.2 engines, clapped out ex london rejects they were, held together with chewing gum, spit and hope. These all had the 3 main bearing cranks, being 2.2s . in 1977, queens silver jubilee year, he 're named it jubilee taxis, and splashed out on a brand new fx4, mnc 385p. The only new vehicle he ever had. This had the new 2.5 engine, an alternator, not a dynamo, and those funny little heater plugs in parallel, instead of the 2 volt series things that never seemed to work. It was an improved & updated replacement for the 2.2, with 5  main bearings. I'm wondering now if there was an early version of the 2.5  with a 3 bearing crank, later ones having 5? I was talking to mate of mine today who had a taxi repair business around this time, he remembers bmc 2.5`s having a 5 main bearing crank too. I put one in a series 2 landrover once, was a popular conversion at the time. 

I spent some time working at a firm in Hounslow that ran a fleet of taxis, from memory the 2.2l engines didn't dare well when rebuilt- the bottom end starting to rattle after one or two motorway runs. 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.