Fiat 850 camshaft centre bearing.

ramona300

ramona300

True Classic
I installed a new centre camshaft bearing and when I went to slip in the camshaft it would not fit. Then I consulted the workshop manual and it seems every time you do this the bearing has to be reamed out to suit with the prescribed Fiat tool! Obviously, I don't have the tool and I'm reluctant to return to a machine shop. The camshaft in this case is just there to drive the oil pump. I have machined off all the lobes and lightened it a bit. I guess I could stick the camshaft in the lathe and make it a sliding fit? Thoughts anyone?
 

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The center bearings I’ve seen are a rough finish. The fit at the center bearing has a major effect on oil pressure and especially how much oil reaches the head. Not sure what mods you might have made that changes this.
 
Technique I've used on other motors: cut a relief into an old camshaft that leaves a sharp edge...and then use that as your reamer. Of course, this assumes you've got an old camshaft you're willing to destroy. In case you do, I figured I'd offer up that tidbit of info.
 
Matt Zerega said:
Technique I've used on other motors: cut a relief into an old camshaft that leaves a sharp edge...and then use that as your reamer. Of course, this assumes you've got an old camshaft you're willing to destroy. In case you do, I figured I'd offer up that tidbit of info.
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Actually, that is a good idea. The only problem is the only camshaft I have is the one that originally was in the engine and that's the old type with the thick bearing so the centre of the camshaft is about 5 mm short for that mod. It does offer up other possibilities.
 
NM850 said:
The center bearings I’ve seen are a rough finish. The fit at the center bearing has a major effect on oil pressure and especially how much oil reaches the head. Not sure what mods you might have made that changes this.
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The Suzuki head will have to have an external feed for the oil.
 
For what it is worth, when I had to ream a suspension piece for the amphicar, I used a brake cylinder hone. Took a while, but very controllable, and left a nice finish to it.
 
Daniel Gibson said:
For what it is worth, when I had to ream a suspension piece for the amphicar, I used a brake cylinder hone. Took a while, but very controllable, and left a nice finish to it.
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This was suggested to me last night at a car club meeting by a well-known race car engine builder. I just bought one off eBay for 20 bucks. Thanks for your help.
 
ramona300 said:
This was suggested to me last night at a car club meeting by a well-known race car engine builder. I just bought one off eBay for 20 bucks. Thanks for your help.
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Be sure to use new stones and plenty of lubricant.
 
What material is the bearing? If it's white metal the stones will probably clog up, if bronze may be ok. There are adjustable reamers available, but new ones that size would be pretty expensive. Congrats by the way.
 
GregS said:
What material is the bearing? If it's white metal the stones will probably clog up, if bronze may be ok. There are adjustable reamers available, but new ones that size would be pretty expensive. Congrats by the way.
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Thanks Greg. Yes it's white metal but should be OK at slow speed with lubricant. I turned up a plastic bearing on the lathe to go in the front bearing to hold the shaft straight. Not much to come off really.
 
Well after several hours of fooling around I have this sorted. The stones did clog up Greg and were slow going. I eventually used an appropriate-sized socket on an extension driven by a battery drill. I taped oxide paper around the socket and ended up with a near-perfect fit! I tried wet and dry paper first lubricated with WD40 but that was slow going. It's a snug sliding fit and should be fine maintaining the oil pressure.
 
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