7A rod compatibility?

[Cuzzo]

http://www.crower.com/pdf/08/157-173.pdf

Check out their new catalogue (2008) it has alisting for the 7afe so you can compare the sizes to the 4age and the mazda rods. All on the same page

[Mooro]

They look pretty close except the big end bore is 48mm for BP and pretty sure it is either 50 or 51mm for the 7a...so same conclusion I came to with the CA18 rods...you need to do an offset grind with the 7a crank...I'd be interested to seee how much that cost but I can't imagine it being cheap so probably better just to buy proper aftermarket 7a rods.

Still keen to hear your measuring results but I fear it is a no go without considerable crank machining .

[jezza323]

here is an excel sheet with a bunch of rod info i did up quickly yesterday, still plenty of rods can be added.

just sort it according to length and look for something with similar b-e journal and b-e width in the same area of the sheet

[Cuzzo]

Im pretty sure the 7afe BE size is 48mm like the 4age

[Mooro]

I have heard that as well but I think it gets confused with the crank journal diameter which I believe is 48mm and the rod big end which I believe is 50mm or 51mm (I think it maybe changed over the years)...I would love to be corrected though

[Cuzzo]

Well im not sure on the difference so i'll sit quite untill confirmed.

[Mooro]

Well I'm presuming the BE diameter on the rod will be bigger to accomodate a bearing shell between the rod and the crank.

[Ben Wilson]

here is an excel sheet with a bunch of rod info i did up quickly yesterday, still plenty of rods can be added.

just sort it according to length and look for something with similar b-e journal and b-e width in the same area of the sheet

That's great - have some +rep

[turbo4agte]

They look pretty close except the big end bore is 48mm for BP and pretty sure it is either 50 or 51mm for the 7a...so same conclusion I came to with the CA18 rods...you need to do an offset grind with the 7a crank...I'd be interested to seee how much that cost but I can't imagine it being cheap so probably better just to buy proper aftermarket 7a rods.

Still keen to hear your measuring results but I fear it is a no go without considerable crank machining .

The thing is your looking at this all wrong. The crankshaft rod journal diamter is 48mm for both. You seem to have looked over this part-- It doesn't matter what the big end bore is!!

All that matters is the crankshaft rod journal diameter. For example with a BP rod you'll use a BP bearing, and with a 7A rod you'll us a 7A bearing. Both of them give the same oil clearance on the crank which is around 0.0006-0.0015. If you use the rod with corresponding bearing you should get the same oil clearance. If your trying to compare big end bores, your automatically assuming all bearings are the same thickness and all recess in the rod the same which is false.

[turbo4agte]

As far as the big end width goes (completely different from big end diameter) the ZIP file posted above lists the 7A rod at 21.7mm(0.854") and the B6 rod at 21.8(0.858") a 0.004" difference and the Crower PDF file posted above lists the 7A rod at 0.858"(21.8mm) and the B6 rod at 0.860(21.85mm) a 0.002" difference.

So either way were looking at a 0.004" maximum difference and the connecting rod side clearance spec for a 7A is anywhere from 0.0059-0.0098". Up to a 0.004" difference.So its a pretty wide window meaning the B6/BP rods should be good to go in a 7.

Well Im off to the junkyard to find a 7A block. Even if I get one and good block and BP rod, my micrometers are at the shop and I wont be back there until Monday.

[Mooro]

Well I hope your right

I still can't quite see how the BP crank journal is 48mm given that the rod big end is listed as 48mm so there is no room for a bearing shell...but I'm certainly no expert.

I really hope your right

[turbo4agte]

Well today I got a BP rod from the junkyard. I found a couple 93-97 corollas, but most had 4As or the engine pulled. One had a full 7A block but it had been waterlogged because someone left the hood open after they pulled the head. Im going to another yard tommorow to see if I can get a good block and crank.

As far as the big end diameter its not 48mm its listed as 2.006" for the 7A and 2.007" for the BP both approximately 51mm, atleast according to the listing above. But like I said all that matters is the crank diameter. I have the service manuals for both engines and they both list the crank diameters at 48mm. I could even get you the service limits in standard inches for both, but am not in the shop right now.

Wish me luck for tommorow.

[jezza323]

Wish me luck for tommorow.

good luck tomorrow

[terryo]

The 4A cranks use a 40 or 42mm big end pin. The 7A uses 48mm. You can easily offset grind the 7A crank to whatever size you want down to about 39mm and increase the stroke even further. this then required different length rods and/or piston heights. The other problems with alternate rods is the width of both big and and little end. Both are easy to narrow. We can get a 7A to almost 2 litres. I do this stuff at work all the time

[Mooro]

Does head flow become a major issue on a 2L 7a? IN the sense that a head designed to support a 1.6L engine now has to flow enought for a 2L engine or is it easily overcome?