843cc engines

[Kent Baird]

I have some 843cc and 817cc engines that I need to do a performance redo. Reverse CW rotation in my 600 and CCW in the 850 car. I have some of the parts. But I have some questions.

Has anyone offset bored the 843 block to use the 67.2mm size 965 engine style pistons?

The cheap Chinese connecting rod sets on eBay have the floating pin size of 18mm and 110mm length. Are pistons available for the 63.5 stroke.

If you put a 903 crank in the 843 block and 843 rods. Do you have get custom pistons made or can you machine the stock piston tops off 2mm?

I have a 70mm Giannini crankshaft and stock 843 rods. What can you use for pistons?

Can the 850 3-bolt water pump fit and run CW in a 600 car?

I had planned with John Edwards to install a special center cam bearing to use a 600 camshaft in the 850 block. Does anyone know of a machine shop doing that kind of stuff these days?

Thanks,
Kent B.

 

[Frank L. Di Gioia]

Kent,
For what it's worth years ago I machined 903 pistons to fit a 74mm crankshaft in a 903 block using 843 rods and it worked. HOWEVER it had rather high compression when used with a PBS 8-port head. Something like 180 PSI on a compression test. Ate plugs till I found a motorcycle plug that held up. We're talking 20 miles before they shorted out. I just sold an 843 motor with a 903 crankshaft and 110mm rods but it did have special pistons. Last but not least I just got a set of the Chinese rods and they look fine (means nothing) but will probably drill a small end oiler and add lower oilers (holes) for the piston bottoms.

 

[Kent Baird]

Hi Frank,
My block needs the bore up sized.
So I was hoping to find some larger pistons to fit on the MaxSpeed 18mm pin rods.
Changing to the larger crank is going to be custom pistons I guess.
My 600 car is a lite weight street car. So if I can get around 65hp I would be happy.
My plan was to use a hot 600 cam so I could use the simple mechanical fuel pump.
Also I wanted to save $$ on not getting the gear drive set.
I have a 127 cam but no fuel pump lobe.
Thanks for your input.
Kent

 

[Frank L. Di Gioia]

Hi Kent,
As to the water pump question go to Ebay and punch in "post water pump fiat 850-850 special" and it has a Fiat water pump impeller for a good pic out of the housing. . It's NOT directional and IF it's the same as the 843-817 impellers it will go either way and work but maybe not quite as efficiently give the shape of the pump housing. I asked Clark at PBS once about the short pump they made with the Toyota impeller and he said about the same thing.
As to the 843 block taking the 67.2 bore I don't know but do have an 843 block with some damage to it. A rod slapped the lower cylinder web on one side and took out a chunk. It's actually similar to what you need to do to a 903 block to run a 74mm crankshaft. That and an overzealous person overtightened the oil pressure sender threads and broke out a piece. Both faults shouldn't actually effect running but look bad. It's semi set up for reverse oiling as the center main is drilled to the oil gallery. If you pay freight I'll send it to you to "test bore" to see if 67.2 works. If it won't, trash it. If it does you owe me for whatever you think it's worth. I wish John Edwards was still with us, RIP.

 

[Frknfiat]

Al Consentino aka FAZA and Art Bayless sold conversion pistons for putting a 903cc crank into 843 block, using a stock 843 rod, clearance internal block for crank throws as needed.
I would convert from 9mm head bolts to 10mm - then conversion works fine, compression not an issue, but you could trim off pop-up part of piston if you have a heavily resurfaced head - looks like the last of Art's old-stock cast pistons are finally sold out at the "new" Midwest Bayless (?)

https://www.midwest-bayless.com/p-1...mm-fiat-850-for-903-crank-w843-block-new.aspx


Yes, trimming off the top of any stock Fiat 850 piston by 1/2 of the stroke increase will work, safe with 68 stroke, 74mm stroke is another issue, listen to Frank's comments.
Find early 850 3-bolt water pumps - must have a 24mm exit tube not the 30mm, BUT some of the 30mm were universal direction too - your looking for early pumps used on 850 sedans that came out right after end of 600D.
You use an early 850 1st series rubber fan bellows and 850 top bracket that holds the bellows.
This pump has straight pump impellors so it can turn CW or CCW - cool if you know this, yes, 843cc block has thicker cast iron block where pump mounts, but the fan hits close enough on the 600 radiator, easy fix, deal with it, the 600D water pump will have the same issue on 843cc block.

here is a 30mm tube version of the 843cc water pump:

 

[NM850]

Last but not least I just got a set of the Chinese rods and they look fine (means nothing) but will probably drill a small end oiler and add lower oilers (holes) for the piston bottoms.

For what it worth....in my other orbit of Alfa engines I learned this. A company in England ran the Maxspeeding rods in a full race engine to 9000 rpm. Then the engine was torn down and the rods were X-rayed, cut up and Rockwell hardness tested. This company found no difference between these “cheap” rods and very expensive US rods.
I myself use them, only to about 8000rpm. When weighing them, both over all and end to end they are exactly then same. I use ARP bolts and I think most sellers provide these. In short I would not hesitate to run them.

 

[myredracer]

According to Paul V., the max. bore for an 817/843cc block is 66.4mm.

A 903 block can be bored to 67.2 but the bores have to be offset like in an A112 motor. Paul put together a 1050cc motor for me using a 903 block and A112 crank, rods and pistons. I used an A112 head too, partly due to the increase in CR. An A112 crank can have the mains bearings safely ground down to 903 dimension and you don't need to align bore the main bearing saddles in the 903 block that way. A 903 and 1050cc block are taller of course. This is an expensive route to go so fuggedaboutit.

A 68 mm 903 crank can go into an 817/843 block.

There's also notching of the cylinder walls at the bottom to clear the rods with a larger stroke crank and IIRC, narrowing of one of the lobes on the cam. Paul V.'s excellent writeup on engine builds can be found on the internet and Mahlon Crafts website may have some useful info. Greg Schmidt's Tips & Tricks can be found on the 'net.

Jeff Stich will have some good info. if he comes along.