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A15 crank wil NOT fit in A12 block
No life (a.k.a. DattoMaster)
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So as clearly I was bored yesterday I tried an A15 crank in an A12 block and there are issues.

First the block in question was a 73.75mm bore. My intent was to use 75mm Honda Pistons in my A12A block

I used the standard A12 rod and piston (knowing th piston was going to stick up 2.5mm), the connecting rod fouls the bore. I didn't measure but the top of the rod bolt contacts the bore so I'd say it needs at least 5mm more clearance.

Next I pulled the rod and piston off the crank; the crank throw contacts the block about a 1/3 of the way along the surface of the throw.

So a couple of things; an A14 crank may fit without these issues given the shorter stroke, the A15 crank might clear the A12A 75mm bore block but I doubt it so I won't be trying it.

Posted on: 9/8 17:24
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Re: A15 crank wil NOT fit in A12 block
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Reportedly it has been done

Good to know about the rod bolt clearance. Boring out the A12 to use 76mm pistons is likely required. Preferaby a short-skirt piston so that crank machining & rebalancing is not required

The side clearance is a well-known issue. The A14/A15 block is notched inside (very slightly) to clear the crank throws. Hard to tell the difference by eye, so perhaps the A12 block can be likewise clearanced
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The A15 oil pan bolts up to a late A12 or A12A block

Attach file:



jpg  A15 oil pan reliefs 25715.jpg (32.98 KB)
174_5d75777945818.jpg 592X336 px

Posted on: 9/8 23:20
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Re: A15 crank wil NOT fit in A12 block
No life (a.k.a. DattoMaster)
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A15 crank with a12 rods gives 1.482 rod stroke ratio
original is 1.622 so its a big difference unless its
turbo with 5500rpm rev limit.

Posted on: 9/9 10:27
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Re: A15 crank wil NOT fit in A12 block
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1.482 rod/stroke ratio will still rev to 7000 rpm. Remember a stock A12 is long rod motor, so going shorter is not a deal-breaker. The small-block Chevrolet 400 has a factory-designed ratio of 1.48 and had a bad reputation due to that -- but it can rev to 6500 rpm -- and thats with 95mm stroke compared to A15's 82 mm stroke

rod/stroke ratio is important when you are racing and limited to a certain cubic inch limit. Since you and your competitors are running the same size engine, a little bit of advantage of R/S ratio might give you the edge. Even a few hp might win the race

Posted on: 9/9 11:07
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Re: A15 crank wil NOT fit in A12 block
No life (a.k.a. DattoMaster)
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yes but the majority of chev 400 guys change the rods to 5.7 or 6 inches
yet if the A15 can do 7000rpm with that rod ratio no doubt the cam timing
is less of an issue with all that speed moving away from tdc.
Problem is you need lots of valve and port size to make the most of it
hence Nissan used long rods to make full use of the chosen valves/ports etc

A12 with 1600cc would be nuts but Id definitely get some piston teflon coatings
thinner rings to reduce friction and as 400 rebores a Torque plate is a must.


Modern engines use short rod stroke ratios but with offset bores from crank centerline to soften the sideload on the power stroke.

Posted on: 9/9 14:07

Edited by D on 2019/9/9 14:24:11
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Re: A15 crank wil NOT fit in A12 block
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400 Chev is a great motor. All this talk about bad design , over heating is a Myth . People put 6 inch rod in them to reduce stress on the cylinder walls when reaching over 500 hp. I think standard their 5.56

Posted on: 9/9 14:40
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Re: A15 crank wil NOT fit in A12 block
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We put my 1527cc A12 short block together over the weekend. Yet to be proven but early A12 block, A15 crank, late A12 rods (small end opened up) and modern 77mm Mini Cooper S pistons. That combo came up flush with the deck - will upload pics tonight.

Posted on: 9/9 19:45
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Re: A15 crank wil NOT fit in A12 block
No life (a.k.a. DattoMaster)
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I seem to recall the Mini has 21mm pin but yes the pin height is 26.5.

Was the A15 crank modified at all?

Were the Mini pistons OEM/replacements or from someone like JE, Wiseco, Wossner etc?

Posted on: 9/9 21:00
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Re: A15 crank wil NOT fit in A12 block
No life (a.k.a. DattoMaster)
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oh to hear someone going the road less travelled!!!!
pure delight! bushed piston pin bores?

for those interested in a little history of the new Mini engine

Quote:
Tritec Motors Ltda In 1997, Chrysler Corporation and Rover Group (then a subsidiary of BMW) formed a joint venture called Tritec Motors to design a new small straight-4 engine. The new company built a factory in Campo Largo of Curitiba, Brazil specifically to manufacture the new engine. The Tritec name stands for the union of the three countries involved: Germany, the United Kingdom, and Brazil. When BMW broke up the remains of Rover Group in 2000, BMW kept the stake in Tritec Motors as the engine was in use in the Mini range which BMW had retained.



For the chev 400 it has 105mm size pistons while the datsun 77mm in this case
95mm stroke vs 82mm stroke. I wonder if there is a formula to calculate how
much force there is on the side walls with the changing diameters and strokes.

The short stroke ratios usually make use of massive port heads as usually
found in multivalve engines today. However I also wonder how much better this
ratio would be for spooling a small turbo so there is zero lag.

Ive been wondering how these late 1.4-1.5 vw and bmw turbo engines are making
v8 type torque and v6 type power with no lag at all. Driving a 1.4 vw we had
50mpg crazy power everywhere yet no visible lag. Can this be done with an A12
with that capacity, it would be very sweet. The short ratio creates supersonic
speeds that favor boost or race engines as mentioned.

Posted on: 9/10 6:07

Edited by D on 2019/9/10 8:47:04
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Re: A15 crank wil NOT fit in A12 block
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Pics as promised. These are a 77mm Mahle forged piston out of a standard BMW Cooper S Mini that had run a big end.

The initial plan was to run a RB20 rod (121.5mm long same as a12) and had a 21mm small end same as the supercharged mini pistons. This plan failed when we hit the oil gallery clearancing the block because there was to much meat around the big end of the rod.

Plan B - use some late a12 rods. They have the same meat on the OD of the small end as an A12A rod (19mm pin) so they were opened up from 17.45mm to 21mm. Engine builder was plenty happy with opening them up to 21mm. The block then only needed minor clearancing for the rods. The crank itself spun in the block when doing a dummy up years ago.

Crank did need machining. Counterweights turned down slightly and flat spots added for clearance at BTC - see pics.

Attach file:



jpg  67741564_2450322045030825_5601037705065529344_n.jpg (61.10 KB)
16379_5d77f29106d79.jpg 720X960 px

jpg  67520582_2450322121697484_533638511023095808_n.jpg (55.38 KB)
16379_5d77f29ce55ce.jpg 720X960 px

Posted on: 9/10 19:59
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