97 MXV wrote:I am on lookout for good long nose big bolt pulley hub type crank and maybe block.
Now if solid lifter head has higher value, then buying a later FWD engine for part out may be an economic option as such cranks do not come up that often.
So how does one tell by
these ebay photos what year this particular head and crank might be ?
Mine was the winning bid on ebay for a dodgy condition/spec motor the owner had acquired years ago from an unknown donor car with unknown mileage.
Following strip down, I discovered that I won out on really good block and pistons
but lost out on head and the crank.
The head is not the later solid lifter type but the earlier hydraulic valve lifter type BP05-8-2 in what appears good condition despite the blown gasket.
The crank was a total surprise !
The crank (top of the picture) is marked BP02 and looks a the poverty pack lightweight big nose crank seen here compared with later big nose (forged BP MX5 I was expecting) and the early long nose (forged early 323/Laser BP) bottom of picture.
Note that both the big nose cranks shown suit the MX5 BP style pulley boss design. The differing lighter crank design (minus 4 counterweights) begs these brain teaser questions....
- What is the performance capability of this lighter crank ?
- Is it the same cast crank I read was fitted to SOHC engines ?
- If cast is it cast steel or a tough form of cast iron ?
(Toughness coming from spheroidal not flaky graphite inclusions seen in the "quiet" and machinable but brittle grey cast iron of engine blocks)Undeterred, the outcome from all this discovery will no doubt be a renewed quest for a forged big nose crank from a FWD.
Now another interesting but off topic find is the matching slotted pulley for the lighter crank.
Before coming across this I had assumed slotted pulleys were ADM B6 V belt type and unslotted pulleys were BP multi rib belt type.
But this is an 8 slot pulley to suit a multi rib water pump/alternator belt, not a V belt pulley.
The other interesting thing is the design of the rubber layer and "decoupled inertial mass" part of the pulley is totally different also.
The slotted pulley design has belt drive to the aircon and power steer directly from the hub part of the pulley and has belt drive to the water pump and alternator belt from the decoupled part of the pulley.
On the other hand a typical 1.8 MX5 non slotted pulley has belt drive to both belts from the decoupled part.
There are subtle differences in theory between belts dríven directly and belts dríven off the decoupled part through shear of the bonded rubber layer.
(BTW "bonded" could be friction bonded or adhesive bonded....not sure how Mazda bonds theirs).
Theoretical differences aside, the practical differences seem to be the following:
- the slotted pulley appears to have a lighter decoupled mass
- the slotted pulley appears absolutely fail safe.
The slotted pulley would fully capture the outer decoupled part should the rubber layer fail at high rpm. This seems a more robust way to design it.
A non slotted pulley however does not appear to have this fail safe feature.
This difference in design does beg the question...
What is the rubber layer failure mode of an MX5 BP style pulley ?
Can the outer rim (the decoupled part of an MX5 pulley) detach and spin off at high revs out of control if the rubber ultimately loses retention ?
Therefore something to ponder for a future topic devoted to crank pulley options will be whether MX5 BP style pulleys meet
SFI SPECIFICATION 18.1 ?
