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Stupid noob question?
https://www.ausmini.com/forums/viewtopic.php?f=5&t=67896		 Page 1 of 2
Author:  Tito [ Tue Dec 28, 2010 6:09 pm ]
Post subject:  Stupid noob question?
I tried doing a search, with out much luck. Can someone tell me what the differences are between A and A+ motors is please?
Author:  Phat Kat [ Tue Dec 28, 2010 6:49 pm ]
Post subject: 
Hey Tito :)

The differences you will notice when looking at the two blocks side by side, are...

.A+ has webbing on the block

.A+ has a correctly possitioned alternater boss in the casting (the original A series was designed for a dynamo, which were longer in the body so when they went to the alternator, they started using an adapter bracket)

.A+ has thicker flanges (sump rail)

.A+ has an extra crank case breather

.A+ has a different timing chain cover (because it has a chain tensioner)


Meeeeeeyeah those are the main differences you'll see from the out side.

Of course there are other internal differences, such as different oil way drillings in the cranks, the cranks in the A+ 1275 engines (and maybe the 998's, I'm not sure) from (about 82-83) onwards had fillet radiui on the journels where the webs meet making them stonger... the conrods are differnet, the oil pumps have a different drive (slot, not spider or pin), the camshafts in the A+998's all had 1/2" lobes (as apposed to 3/8")... the gearboxes are different... there are other differences but thats all I can think of off the top of my head.

Is either better? Depends who you ask. Some argue that the material used for the earlier blocks was better and that the quality of the casting was better (some of the early A+ blocks had porosity isssues).. Certainly the design of the A+ is better, with the extra webbing and thicker flanges the design is more ridged.

Depends who you ask... others will tell you what they reckon soon no doubt :)

Cheers
Author:  Morris 1100 [ Tue Dec 28, 2010 6:57 pm ]
Post subject: 
As well as those that Phak Kat has listed on the A+ the distributor is held in with a forked clamp instead of the usual type of clamp.
Author:  GT mowog [ Tue Dec 28, 2010 7:29 pm ]
Post subject: 
WARNING:

If it is a 1275 A+, that uses the plain half slipper bearing in the Main Cap, NEVER fit a pre A+ Crank to it. The A+ Cranks are a different size and the Mains are Cross Drilled. There are some who have found out the hard way.
Author:  drmini in aust [ Tue Dec 28, 2010 7:36 pm ]
Post subject: 
The thicker sump flange, extra breather on timing cover and timing chain tensioner (also the A+ sintered rockers) all came in years before the A+ production started in 1980.

Which is better? A series I'd say, if going for big HP.
1. Better castings on A series- most A+ blocks got sleeved by the factory due to porosity issues.
2. A+ lower main bearings with stock A+ crank (not cross drilled) starve the big end bearings of oil, which wear out sooner. This is because the big end bearings only get oiled for 1/2 each revolution. I mod the caps to take A series bearings.

However, otherwise most A and A+ bits interchange, so run wot ya got.

[edit] A+ cranks are NOT a different size to an A series big journal crank.
Author:  GT mowog [ Tue Dec 28, 2010 7:41 pm ]
Post subject: 
drmini in aust wrote:

[edit] A+ cranks are NOT a different size to an A series big journal crank.


Sorry mate, it is not widely known, but they most definitely are :wink:

<EDIT> Likewise never try putting an A+ in to a pre-A+.
Author:  drmini in aust [ Tue Dec 28, 2010 8:35 pm ]
Post subject: 
GT mowog wrote:
drmini in aust wrote:

[edit] A+ cranks are NOT a different size to an A series big journal crank.


Sorry mate, it is not widely known, but they most definitely are :wink:

<EDIT> Likewise never try putting an A+ in to a pre-A+.

OK I'll bite, give me ONE dimension that is different... :lol:
I know people running stroked and stock A+ cranks in A series, and A series cranks in A+.
Author:  TheMiniMan [ Tue Dec 28, 2010 10:15 pm ]
Post subject: 
I`d like to say (now that this topic has been brought up) the "non" grooved lower main bearing half (on some of the later Metro A+ type blocks with central tang) isn`t an issue like some people like to suggest,,, it if were an issue with oil feed on these types of bearing then "All" big end bearings in all engines should also be an oil feed problem too yeah???,,, no central groove in any of those right? so why would there be an issue with oil feed on the A+ center main lower-half???

just thought i`d bring this up cause it`s erked me for some time ;-)

& sorry GT, but i don`t get what you mean about A+ crank measuring different to pre-A+ ???
Author:  Morris 1100 [ Tue Dec 28, 2010 10:19 pm ]
Post subject: 
My A+ book says the main bearing size is different. But I bet my book has never changed a crankshaft. :mrgreen:
Author:  TheMiniMan [ Tue Dec 28, 2010 10:47 pm ]
Post subject: 
i`m betting it`s listing tighter "Allowable tolerances" being the issue yeah???

Ah ,,, Books shmooks,,, they`re over rated in my books :-)

what good did reading books do for anyone anyways??? :-)
Author:  david rosenthal [ Tue Dec 28, 2010 11:26 pm ]
Post subject: 
The bearing shell without the groove was designed to give better "hydro-dynamic" lubrication. This is where the oil film is compressed to float the crank. Many high crank load big marine engines use this system where the top shell has a groove to supply the oil and a non grooved lower shell.
Author:  goodie [ Wed Dec 29, 2010 8:10 am ]
Post subject: 
This should be a good debate!!. 6 of the best posters having a good strong , interesting,
imformative , educational debate on an issue that should help a few people i'm sure, keep it up fella's , it's great reading .

PS: ( keep it clean! )
Author:  drmini in aust [ Wed Dec 29, 2010 12:43 pm ]
Post subject: 
I recently reconditioned a 1293A+ motor where the 3 mains were fine, but all 4 big ends had .007" YES, 7 thou! ovality. Had to regrind them, but the mains were still on size.
I fitted A series bearings instead (after milling an extra bearing tang slot into each mains cap). At least now the big ends get lube pressure all the time, not 1/2 the time... No, the A+ crank wasn't cross drilled on the mains (another way that some people fix this problem).
Fitting A series mains is a common mod on A+ race motors.

Note that ACL main bearings run less clearance than most others- if you're gonna race with em, I'd add 1/2 a thou approx extra clearance when grinding the crank.
Author:  Phat Kat [ Wed Dec 29, 2010 1:05 pm ]
Post subject: 
drmini in aust wrote:
Note that ACL main bearings run less clearance than most others- if you're gonna race with em, I'd add 1/2 a thou approx extra clearance when grinding the crank.


Hey Kev :)

I have a pair of virgin cranks A+ up in the pallet racking. I'll be honest with you, I'm still not sure on this so I'll get them down and Mic them up.

I agree, for racing applications, more clearance than the factory 0.001" is preferable. Even in road engines I like to run a little more than that.

On the topic of the ACL beaing shells, the 1100s that I was blueprinting over the weekend (the one I mentioned to you) was running ACL's in it.... the main journels read 1.990", 1.9905" and 1.990". Bearing clearances were between 0.0015" and 0.0017". If anything, the bearings are looser... Where you refer to "ACL bearings running less clearance" do you mean specifically in regards to A+ bearings or all bearings...
Author:  drmini in aust [ Wed Dec 29, 2010 1:33 pm ]
Post subject: 
Going on what GR advised me, it is ACL Duraglide 780 bearings, A series and A+.
They are excellent bearings , just don't run em too tight. :wink:
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