NickJ Posted January 24, 2017 Share Posted January 24, 2017 Trying to track down rings for the fiat twin cam in the Niva and as the engine is of the older 1600 variety parts are a little scarce, so far i've only been able to get rings in 80.2mm bore, currently the bore measures as 80.0 but after a hone that may open up a touch, is it legit to open the gap on the oversized rings to fit into 80.0mm? I assume the pistons would need to be replaced if I had the bores opened to 80.2? What is the opinion on bearings, (big and main) even though they measure up good and show little sign of wear, is replacing them because the engine is out a good call, or is it a case of don't fix what is not broke? Quote Link to comment Share on other sites More sharing options...
azzurro Posted January 24, 2017 Share Posted January 24, 2017 I would file the rings a smidge if needed but im sure its not good practice/im an idiot (also your bores have worn from the nominal 80.0mm from use (and a hone, surely?), and the circumference difference is only 0.25%, so yeah) re bearings, replacement is always a good call 'while your in there', but if you reckon they are fine, they probably are. Ive done this on a few engines, and my justification was they will be no worse than before! 1 Quote Link to comment Share on other sites More sharing options...
NickJ Posted January 24, 2017 Author Share Posted January 24, 2017 My reading indicates checking and adjusting the gap like you say is ok, but to downsize that far may be taking the piss. Now that I have the wideband and planning electric ignition, it kind seems I should do it all correct. Quote Link to comment Share on other sites More sharing options...
Carsnz123 Posted January 24, 2017 Share Posted January 24, 2017 If you're in Christchurch take a piston to Cliff Bond down ferry road. They have shit loads of NOS rings on the shelf and can match something up. They'll probably give you some good advice as far ay your crank/bearings. 6 Quote Link to comment Share on other sites More sharing options...
governorsam Posted January 24, 2017 Share Posted January 24, 2017 Cliff bond are wizards when it comes to rings. And stuff. In the past they supplied rings to fit an obscure size on a motorbike engine. Machined the ring groove in the piston to suit the bits they had in stock. Was about $300 cheaper than factory ones. Clever buggers. 3 Quote Link to comment Share on other sites More sharing options...
NickJ Posted January 24, 2017 Author Share Posted January 24, 2017 Cheers, I'm going to have to follow up on that, I work over in Hornby which will make getting there difficult, but it needs to happen! Quote Link to comment Share on other sites More sharing options...
Archetype Posted January 24, 2017 Share Posted January 24, 2017 A+ thread title. 2 Quote Link to comment Share on other sites More sharing options...
Hemi Posted January 24, 2017 Share Posted January 24, 2017 Bearings are like$50? I'd do them while everything is apart, you're there anyway. Quote Link to comment Share on other sites More sharing options...
Mr Vapour Posted January 24, 2017 Share Posted January 24, 2017 Do the big ends at least. It's not uncommon if you replace the rings and leave the b.e that the bearings fail not long after as the extra compression from the new rings puts pressure on the old bearings and they run or spin. Also the bores being .2 oversize. The first oversize available is often 020 or .50mm so you may get away with a hone. But you could have issues with filing them down that much as the that as the ring may become.out of round 1 Quote Link to comment Share on other sites More sharing options...
Mr Vapour Posted January 24, 2017 Share Posted January 24, 2017 12 hours ago, Carsnz123 said: If you're in Christchurch take a piston to Cliff Bond down ferry road. They have shit loads of NOS rings on the shelf and can match something up. They'll probably give you some good advice as far ay your crank/bearings. Do this. I often sold rings by bore size and the good re conditioners would then machine the pistons to suit the rings. give your bores a hone, remeasure then go talk to the ring specalist in the area. Its alot of work to do if the bores are to far out and you need pistons.. Quote Link to comment Share on other sites More sharing options...
Testament Posted January 24, 2017 Share Posted January 24, 2017 if the bearings are in spec for the journal and show no signs of damage swapping the bearings is not going to achieve anything. journal bearings just work if the clearances are right and the oil system is good i.e. adequate pressure and flow and temperature acceptable then metal is not touching metal and everything goes on forever providing the oil is kept happy. if there is detonation or something that causes metal on metal a new bearing will be ruined just as much as a perfectly good used one. 3 Quote Link to comment Share on other sites More sharing options...
Rookie Posted January 25, 2017 Share Posted January 25, 2017 Tom is on the money here, no need to replace bearings that are in spec. Quote Link to comment Share on other sites More sharing options...
Testament Posted January 25, 2017 Share Posted January 25, 2017 for reference see video below. regarding rings it's pretty ghetto what you are suggesting, have you looked on ebay/rockauto/amazon it is surprising where some of this stuff turns up esp. rockauto has some funky shit if you look through all the models that might have that size piston. just can be a little tedious. Quote Link to comment Share on other sites More sharing options...
NickJ Posted January 25, 2017 Author Share Posted January 25, 2017 6 hours ago, Testament said: if the bearings are in spec for the journal and show no signs of damage swapping the bearings is not going to achieve anything. journal bearings just work if the clearances are right and the oil system is good i.e. adequate pressure and flow and temperature acceptable then metal is not touching metal and everything goes on forever providing the oil is kept happy. if there is detonation or something that causes metal on metal a new bearing will be ruined just as much as a perfectly good used one. This is along my thoughts on the subject, the issue with the bearings is most I can source are metric sizes, while the mains and BE are currently 0.010" oversize which are proving a little more difficult. 9 hours ago, Mr Vapour said: Do the big ends at least. It's not uncommon if you replace the rings and leave the b.e that the bearings fail not long after as the extra compression from the new rings puts pressure on the old bearings and they run or spin. Also the bores being .2 oversize. The first oversize available is often 020 or .50mm so you may get away with a hone. But you could have issues with filing them down that much as the that as the ring may become.out of round This is what i've been told, but I can't see how extra load is put on the bearing, my thoughts are reassembly caused a slight difference in clearance? 1 Quote Link to comment Share on other sites More sharing options...
Mr Vapour Posted January 25, 2017 Share Posted January 25, 2017 If you unbolt them you will release them.slightly. It's also the extra load from the extra.compression. if the bearings have been working with 90psi on a comp gauge then you rering it and end up with 120-130 every stroke there is a bunch more load. And if the bearing has worn 3-4thou and the extra compression. it's going to fail. Only way I.would.be happy would be to visual inspect the bearing any kind of wear, removal of a layer replace. If they are still good then plastic.gauge them and.see what the clearances are. This will give you a real idea of how out of spec the bearings are.not just the crank Quote Link to comment Share on other sites More sharing options...
NickJ Posted January 27, 2017 Author Share Posted January 27, 2017 Took the bits into Cliff Bond today, the boys there were bloody good, after a measure up it became apparent someone has been at the pistons before now, (and made bit of a mess) but they managed to find some old stock mazda rings on the shelf that can be massaged to fit. I'll strip the block fully this weekend and drop it off monday for them to work their magic. I also put a piston through the ultrasonic cleaner at work, tore the bulk of the carbon off really well, might just cycle the rest through. 5 Quote Link to comment Share on other sites More sharing options...
Rookie Posted January 29, 2017 Share Posted January 29, 2017 On 25/01/2017 at 07:12, Mr Vapour said: If you unbolt them you will release them.slightly. It's also the extra load from the extra.compression. if the bearings have been working with 90psi on a comp gauge then you rering it and end up with 120-130 every stroke there is a bunch more load. And if the bearing has worn 3-4thou and the extra compression. it's going to fail. Only way I.would.be happy would be to visual inspect the bearing any kind of wear, removal of a layer replace. If they are still good then plastic.gauge them and.see what the clearances are. This will give you a real idea of how out of spec the bearings are.not just the crank Oh man, I don't even know where to begin telling you how wrong you are. Basically ignore this advice; you can't visually inspect a bearing unless it is munted, the only way to do it is with mic's. Alternitively, it is a low load tractor motor so just put them back in if it is running fine now, it will be running fine afterwards. Quote Link to comment Share on other sites More sharing options...
NickJ Posted January 30, 2017 Author Share Posted January 30, 2017 On 29 January 2017 at 13:08, Rookie said: Oh man, I don't even know where to begin telling you how wrong you are. Basically ignore this advice; you can't visually inspect a bearing unless it is munted, the only way to do it is with mic's. Alternitively, it is a low load tractor motor so just put them back in if it is running fine now, it will be running fine afterwards. That makes sense to me, as I understand it being that the bearings don't really do anything, if they measure up and the increase in load (from less combustion blow by) causes failure, new bearings of the same dimension will fail too, ie there is an oil issue. Quote Link to comment Share on other sites More sharing options...
Rookie Posted January 30, 2017 Share Posted January 30, 2017 Bingo. 1 Quote Link to comment Share on other sites More sharing options...
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