I have an 'AW' engine with 90mm pistons ... ??

hayseed · Post by **hayseed** » Sat May 09, 2009 7:05 am

I just tore down my '74 bus engine (S/N AW014464) and found the cylinder bore to be 90mm. The label on the fan shroud says AW 1974 109ci, which should be 93mm X 60mm. The head casting numbers are '021.101.371.J'. The outside diameter of the head end (and the case end) of the cylinders is 100mm ... cylinder walls are 5mm. Did someone put some sort of aftermarket 'down-sized' P/C kit on this engine ?? Can I replace them with a 93mm X 60mm set ??
... thanks in advance

busman78 · Post by **busman78** » Sat May 09, 2009 7:45 pm

Yes and you will need to open up the head registers from 100mm to
105mm. Seems your engine got rebuilt and the builder used 1.7 parts.

1.7 & 1.8 had 66mm stroke.

Post by **Piledriver** » Sat May 09, 2009 9:02 pm

The PO may not have been an idiot...

You have 1700 heads... Consider "going with it", a 1700 is a little short on power, but is just about the most bullet proof T4 you can have.

Do the pistons have domes by chance?

If they do, that high CR 1700 puts down more power than the 1.8 bus motor ever did.

Replacement pistons (assuming you need them) will be a little hard do come by, which is why I'm turning down the OD on 93mm jugs to fit the 1700 heads... Better head seal, better cooling.

The resulting CR will be about theh same as the 1700 w/domes.

If you do replace the jugs, be careful with them as someone will want them to rebore to 90.5mm. (Something you may wish to consider as well)

Good used jugs rebored are better than anything you can buy today short of Nickies.

fusername · Post by **fusername** » Tue May 12, 2009 3:32 pm

I have a set of rusty 1700 low CR pistons/cylinders with only one broken fin. are you saying I should protect them and sell em when I am done? I am using them to mockup an engine and check my tinwork/exhaust ideas.

Post by **Piledriver** » Wed May 13, 2009 6:04 am

fusername wrote:I have a set of rusty 1700 low CR pistons/cylinders with only one broken fin. are you saying I should protect them and sell em when I am done? I am using them to mockup an engine and check my tinwork/exhaust ideas.

Yes, at least the cylinders.

raygreenwood · Post by **raygreenwood** » Wed May 13, 2009 11:27 am

Pile.....did you notice a while back that AA psitons sells domed 1.7's with wrist pins and rings ......just pistons ...for about $165 a set. If they are decent, thats a great price! They are 90.5's.

Whats the quality like on AA pistons these days? They were very prompt in their reply to my inquiry. Ray

Post by **Piledriver** » Wed May 13, 2009 4:00 pm

I haven't used them, but reports are the newer jugs are a bit soft... FAT sends the AA jugs out for heat treat... I'm thinking ion nitride would be an excellent (but expensive) solution.

AA pistons have a bad reputation as to ring groove tolerances, but again, the only set of AA pistons I have personally used are for a WBX, and they were OK.

WestyPop · Post by **WestyPop** » Wed May 13, 2009 11:10 pm

Not to take this OT, but... is it even safe to ask about the oversized (96mm?)P&Cs to slip-in to 1.7/1.8L motors? IIRC that comes up @ about 1911cc.

Currently have such an engine assembly that I stopped at "almost completed" status a few years ago, and wanted to use as "temporary" power for a long-term project that needs to be 'drivable' right away.

Any thoughts on said 96 x 66 combo?

(side note: I have had great success with Type 1 88mm slip-ins, after having the cylinder fins aluminum "flame -sprayed" for increased heat-shedding).

TIA

Post by **Piledriver** » Thu May 14, 2009 6:49 am

96mm in 1.8 head/jugs is a non-issue, as they fit as stock, 1.8 as 2.0 have the same 105mm nominal head register and cylinder wall thickness.

96s in the 100mm (nominal) 1.7 register leaves you with a VERY thin sealing surface... but 93s (1800) are IIRC a tad thicker as 94mm T1, and with far less "uncooled" area, and no ring load on the thin area, at least w/stock pistons--turned down 94s would probably also work, but I have not tried it.