Technical Plans for 650 engine and transmission rebuild

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Technical Plans for 650 engine and transmission rebuild

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jjacob

jjacob

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UPDATE

Both engine and transmission have been completely stripped.
ENGINE
The engine I am rebuilding is a very late 650 (1987-88?) with the wasted spark ignition (distributor, but no cap and a dual outlet coil). Engine condition is very good, only found the following worn out on engine.
-Oil pump gears show 0.4mm (0.016in) backlash between gears, should be 0.15mm (0.006in).
-Camshaft has one lobe that is excessively worn.
Rest of the engine is in great shape. Looks like oil was changed often as there is virtually no scoring anywhere.
-Going to reuse the pistons and cylinders and just hone.
-New rings
-0.5mm copper head gasket
-New 30/70-70/30 camshaft and cam followers.
-New rod and main bearings
-New oil pump gears
-34mm intake valves, stock exhaust valves, new guides and springs. Will have the cylinder head rebuilt with hardened valve seats and I will do a little mild porting and polishing. Will have the head ever so slightly skimmed to true up.
Will install an oil filter and cooler arrangement. Not sure how I want to do this. I'll make a separate post to discuss this.
TRANSMISSION
Transmission looks very good. Zero play in all gears and axles, nice and tight. Shows typical wear and chips on first and reverse and the layshaft.
-install new 3 gear kit
-new clutch kit

Much thanks to all those who came before me. I have read your valuable posts which help. Special thanks to Tom - The Hobbler, whom emailed me multiple times giving the best of advice and information.

John
 
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the hobbler

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Hi John;
The work that you are carrying out on your engine and gearbox sounds to be very sensible, and cost effective. A tip---the new oil-pump gears MUST be the same as the ones that you are replacing (model-wise). I am convinced that a lot of the oil-loss problems people have suffered is because they have not replaced like-for-like. Also, don't forget to pack the pump with Vaseline (petroleum jelly) prior to fitting it up. Doing this makes for a much quicker oil-pressure build-up upon initial engine start. It is also a wise move to use 'graphogen' (or similar) on all the cam-shaft bearings AND LOBES when building up the engine. I used to (and still do!) build up my engines with a 50/50 mixture of a thin engine oil and STP. The oil lubricates, the STP holds the lubricant in place until you start the engine up. BUT, don't put the remaining mix or the STP into the engine until it is well run-in (if you do, it won't run-in!). All the best with your project--pictures please.
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jjacob

jjacob

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Hi Tom,

Question on the oil pump gears. I know they have to be the same thickness as the original pump gears that came on this Polish engine. That is 14mm. The original gears were straight cut, replacement gears are available straight cut and "slant" cut, or more helical to me. The slant cut are shown in the Fiat 126 repair manuals. On the suppliers web sites, some of them carry the slant cut and others the straight cut.
As long as the gears are the proper 600/650 engine depth of 14mm and have the newer 7.5mm cam interlock, they should all be interchangeable? I would think the slant or helical cut would both wear better (less gear face slap) and also be quieter (as if we could tell the difference!)
I am wanting to reuse the existing oil pump housing because it looks virtually new. Only the gears (which actually visually look good) show too much backlash.

What's your take on this? See attached pictures.
John
 

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  • slant cut oil pump gears.JPG
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jjacob

jjacob

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Thanks Tom,

I also use STP in my rebuilds as well as engine assembly lube. I have a special molybedenum coating I apply to cam lobes and lifters. It goes on like a spray paint and dries to a dry film layer. Very slippery!
John
 

the hobbler

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Hi John;
I agree, the 126 manuals (for both the 595 and 652 versions) all show 'helical' oil-pump gears. As long as they are dimensionally the same as the original gears, I can see no reason why you can't replace 'straight-cut' gears with 'helical'. Fiat must have had a reason for changing the design---more pressure?--quieter? (!)---longer lasting?---I honestly don't know. Whatever you do decide to use, don't forget to pre-pack the pump. Petroleum jelly gets displaced easily by the oil and just dissolves into the lubricating oil--and you only actually use a very small amount, and it makes a BIG difference in the rate oil pressure is raised.
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jjacob

jjacob

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Hi Tom,

Agreed. I think it is important to point out that grease should never be used inside an engine as it will not dissolve into the oil and you run the risk of plugging up an oil way or slowing the movement of oil.
As you have pointed out, petroleum jelly (Vaseline) easily dissolves into the oil, especially as temperature rises. Also, specific lubes labeled Engine Assembly Lube also will dissolve in motor oil.
John
 

fiat500

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I'm not sure that helical gears do have any practical advantage in this application. Are they after-market mods?
This dog drive? In summary are we saying there is a wider, later version and a narrower, earlier one? How good is the fit in the camshaft? Mine seemed quite loose... original 650 pump to non specific, new, standard camshaft.
 
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jjacob

jjacob

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Hi Peter,

The helical cut oil pump gears are what are shown in the repair manuals. I think the straight cut oil gears appeared on Polish (FSO) manufactured engines on the 126p. I would think that the helical type might mesh together a bit better during running. The gears, no matter helical or straight cut need to be 14mm thick for 600/650cc oil pump/timing cover applications. Earlier versions were only 10mm thick. The thicker (14mm) gears are capable of more oil volume (not pressure). You can put the better oil pump on an earlier engine but the timing cover and oil pump must be the newer thicker gear type. Also the camshaft must accept a 7.5mm wide notched oil pump shaft. I imagine it would be easier and cheaper to machine the 7.5mm down to 6.00 mm rather than change the camshaft.
The notched end of the shaft that goes into the camshaft was 6.0mm in width installed on 500's until 1968, and originally installed until chassis nr. 1.817.680 according to Passione500 site. It changed to 7.5mm after that on later cars.
John
 

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  • 6.0mm oil pump shaft.JPG
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