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Old 1 Week Ago   #1
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Barrels/Pistons scoring. Salvageable?

As a winter COVID project, I'm tearing into my spare 500R motor with plans to rebuild it as a mildly-sporty 595 mill. With advice from thehobbler, I'm going to have the head skimmed and 34mm intake valves fitted and a 75/35 cam. I was hoping/planning to leave the barrels and bottom end alone, but tearing into it, I discovered some mild scoring wear. Pics are attached showing the worst barrel and both pistons. Is this normal wear on these? None of the barrel scoring is significant enough to catch a dental pick and I think it could easily be honed out.

With a little honing, do you think these pistons would suffice? Possibly some 73.9mm rings? I'm trying to avoid a money pit motor, but still gaining/keeping power and reliability.

Thoughts? Thanks in advance.
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Re: Barrels/Pistons scoring. Salvageable?

If these engines are relatively well looked after the bottom will go on for a good mileage. Depending on use it is the top end may wear first although I know of one 594cc engine that went over 100,000miles with only following a normal servicing schedule. Scoring of the bores tends to be axial rather than radial. If you remove one of the piston rings and set it in one of the bores you can check the ring gap to test for wear with a feeler gauge. The tolerances are shown in the workshop manual. If worn then I would go for a light hone and new rings.if within tolerances a light hone and reassemble.
This is my home made honing tool, a folded sheet of wet or dry held in a shaft with small rods. Then run it in my electric drill.
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Old 1 Week Ago   #3
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Re: Barrels/Pistons scoring. Salvageable?

Like Dave, I don't think those marks are from the pistons or rings, but maybe from someone previous to you who manually tried to create some rudimentary honing? It's amazing how long the original honing marks will stay on a cylinder wall.

I've used pistons with similar scoring on them as long as they measured-up OK. Accurate measurements are the key thing to ensure that you have a good rebuild which leaves you without slight misgivings. That's not always possible for everyone, but I have only ever had a rebore when it was obvious that an old engine had seized and then corroded.

This is a link to the before and after of my 594 with a few minutes with a honing tool.

https://www.fiatforum.com/500-classi...ml#post4523169
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Last edited by fiat500; 1 Week Ago at 21:17.
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Re: Barrels/Pistons scoring. Salvageable?

I would be tempted to give the bores a good clean and a light hone---give the pistons a good clean and then measure both the bore and the pistons in order to ascertain what the piston/bore clearance is. On the '595'engine it should be:--between 2.8thou and 3.5thou (0.070mm to 0.090mm)---this is measured 2-1/2ins (57.15mm) down from crown of piston. On post 1974 engines,the clearance went up to between 3.1thou and 3.9thou (0.08mm to 0.100mm). If the piston/bore clearance is within those tolerances put it all back together with new piston-rings.
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Re: Barrels/Pistons scoring. Salvageable?

Just had a quick look 'on-line'--if the bores are too scored to use with the old pistons, Axel Gerstl in Germany has 0.6mm oversize pistons (part number:-01224/2) listed and, there is a pair of oversize (by 1mm/40thou) 595 pistons available on e-bay, number:--252459616516. If you needed either of these to get you out of trouble,getthe pistons and THEN get the machine shop to re-bore the barrels to match the pistons with the appropriare clearance.
As I have mentioned before, in the US of A it might be easier to get a bike shop to rebore the Fiat barrels.
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Old 1 Week Ago   #6
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Re: Barrels/Pistons scoring. Salvageable?

I'm a little out of my depth here in that I don't have in depth knowledge of the 500 - I did help my friend look after his back in the early '70's but we never had the engine in pieces. Remember lots of problems with drive shaft splines though!

I do though have quite a bit of experience rebuilding Hillman Imp engines at home in my own garage and also I used to "mess about" a lot with old British motor cycles (so air cooled engines) I find it hard to understand how any running wear could cause the scoring you show in the bore and I'm in agreement with those above who say that it's more likely someone has previously "attacked" it with some, pretty rough, emery? I think you need to give them a light hone and see how they turn out. Doesn't look like there's much of a wear ridge at the top which is good.

I love your DIY hone. I too made one for myself - to be specific I drew up a picture of what I wanted and then my friend who ran courses in hobby lathe use, when I did the evening classes in car maintenance and welding, machine up the triangular "business end" and threaded it concentrically to tale the drive rod. I made the retaining plates for the emery cloth and drilled and tapped the other fixing holes. It works very well indeed and I'm very proud of it!

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The pistons, from what I can see, look pretty good. I would be giving everything a really good clean up - so the rings need to come off and any deposits in the bottom of the grooves cleaned out. You can use an abrasive paper on the piston crowns and, if you're careful, on the lands between the ring grooves but absolutely not on the piston skirts. This is because some grit from the abrasive is likely to become embedded in the aluminium of the piston and the skirt is in direct contact with the cylinder wall! The piston diameter where the lands are is usually just slightly smaller in diameter, by just a few thou, than the skirt so won't contact the bore wall.

With everything nice and clean check all the dimensions and clearances. First try the pistons in the bores, without rings fitted, gently just by hand, and see if they move full stroke easily without any sign of binding. stop immediately if they bind anywhere to avoid scoring. Then, as suggested above, check with your feelers for skirt to bore clearance as if that checks out OK you don't need to start looking at whether it's pistons or bores which have the wear. Ring gaps need to be checked well down the bore (maybe 3/4 towards the bottom of the bore - never near the top where bore wear will be greatest. - for the same reason the piston skirt to bore clearance should always be checked well down the bore too) also the ring must be absolutely square on to the bore or the gap will not be able to be correctly measured. To achieve this put the ring in the bore and then insert a clean piston upside down - so crown first - into the bore and use this to chase the ring down. This, of course, only works with a piston which had a flat crown! If that all comes out OK then check ring to groove clearances with your feelers.

A rather "strange" wee thing that can catch you out if you find you have a wear ridge at the top of the cylinder but decide it's not enough to warrant a rebore but find your ring gaps indicate new rings would be a good idea is that you may just find you have a small "Knock" after reassembling it with the new rings. What can happen it that the new rings, being completely unworn, will lightly contact the wear ridge when at TDC. It sounds a bit like a worn little end bush. The Anglia engine I rebuilt suffered this and it took me two strip downs to find it. To get over this you can buy ring sets with "Ridge Dodger" top rings. My favourite manufacturer is Cords, here is their brochure which shows the ridge dodger concept: http://www.mayphil.co.uk/creo_files/...s_brochure.pdf

Sorry if I'm telling you "how to suck eggs" above but I've rebuild quite a number of engines - from a 2.0 litre "O" series Ambassador (by gum that was a heavy lump) to several Imp engines, a few "A" series BL units, a 997cc Anglia and a few 2 cylinder DAF "boxer" engines. Also motorcycle and moped engines (the hone would be too big for a moped barrel but probably not relevant as most of them were chromed bores so either absolutely fine to reuse or the chrome surface breaks up and the cylinder is just scrap. There's probably one or two I've forgotten about over the years too. (A VW engine in a beach buggy with head sealing problems comes to mind - that engine doesn't use head gaskets). Your components look, from the pics, to be good enough to reuse. I've used rougher looking components to rebuild everyday "runaround" engines which have subsequently run satisfactorily for years. The big thing has to be cleanliness though - cleanliness is next to ? as the traditional saying goes, and it's never truer than when building engines and gearboxes.

Good luck with it all, do let us all know how it all pans out please - with more pics if possible.
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Last edited by Pugglt Auld Jock; 1 Week Ago at 12:20.
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Old 1 Week Ago   #7
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Re: Barrels/Pistons scoring. Salvageable?

Much appreciated gents! Iíll get to honing, pulling the rings, and do a bit of cleaning and measuring today if I can. Hereís to hoping the rod bearings look good when the end caps come off!

Thanks,
Matt
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Re: Barrels/Pistons scoring. Salvageable?

I forgot to ask, if you don't mind saying, where in Maryland are you? My daughter and her husband were based there for nearly 5 years and had a house just outside Leonardtown: https://leonardtown.somd.com/

We spent many happy hours using it as a base to explore all around and do lots of "touristy" things.
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Re: Barrels/Pistons scoring. Salvageable?

Quote Originally Posted by JumpJet View Post
Much appreciated gents! Iíll get to honing, pulling the rings, and do a bit of cleaning and measuring today if I can. Hereís to hoping the rod bearings look good when the end caps come off!

Thanks,
Matt
Be aware that the big end caps are numbered on the cam shaft side and must go back as they were. Do you know the mileage on this engine?
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Quote Originally Posted by Toshi 975 View Post
Be aware that the big end caps are numbered on the cam shaft side and must go back as they were. Do you know the mileage on this engine?
I do not.
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Re: Barrels/Pistons scoring. Salvageable?

Wise words Jock---one must never be to old to learn! Where about in Edinburgh are you? My wife and I lived up there for 9 years (until I was made reduntant by Gerald Ronson from Heron Rossleigh at the Gylemuir).We initially lived in the old tenement building opposite Leith Hospital (Great Junction Street--right above the chippie)) before moving out to just outside Davidsons Mains.
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Re: Barrels/Pistons scoring. Salvageable?

Quote Originally Posted by JumpJet View Post
I do not.
I asked because I think that all too often people just replace big end shells as a matter of course because they are cheap. The factory originals are best quality , nicely run in but they can discolour on the bearing surface which is often seen as wear.
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Re: Barrels/Pistons scoring. Salvageable?

Quote Originally Posted by the hobbler View Post
Wise words Jock---one must never be to old to learn! Where about in Edinburgh are you? My wife and I lived up there for 9 years (until I was made reduntant by Gerald Ronson from Heron Rossleigh at the Gylemuir).We initially lived in the old tenement building opposite Leith Hospital (Great Junction Street--right above the chippie)) before moving out to just outside Davidsons Mains.
Hello hobbler, I don't (hobble that is) so much since they gave me new knees!

When we first moved back north after our days in London we bought a house in Cousland. I worked in garages to the south and east of the City at that time but when I took up a post in training I needed to be based in North Edinburgh so we moved and we've had two houses in this area over the years. Now about a 20 minute walk from Newhaven harbour and very happy with our house and the neighbours, I don't think we would move again - until the kids consign us to a home anyway!

I know exactly where you are when you talk of Great Junction Street but I don't think your tenement is there today and the nearest chippy certainly isn't opposite the old hospital. Probably the Gold Sea on Ferry road is now the nearest but I may be wrong as we seldom frequent chippies due to Mrs J trying to make me eat "healthy" food! However I've been known to sneak the occasional mince pie - that's a Scottish meat pie, for those who don't know, not a Christmas type mince pie - out the door of Mason's bakery on the roundabout by Newhaven harbour. If you're ever in the area you have to try one, their pies are legendary, but Shhh, don't tell Mrs J! Opposite the old hospital is now new(ish) build residential so probably your chippie went when they were built.

For those reading who will not know, Rossleigh were an Edinburgh institution and well know for luxury cars - Jaguar, Rolls Royce, Daimler, etc. Did you work for them when they had the old workshops in Annandale street? An absolute warren of a place with lots of ramps etc - bit like a multistory car park - easy to scrape one of these large cars on a barrier!

Davidson's Mains I've driven through often but never stopped. However, in the summer, we often take the grandchildren down to the side of the Forth just north of there (We park where that length of dual carriageway is that goes nowhere) and then walk along the promenade with the pram and older ones on their bikes to Cramond where we buy ice creams and look out to the island. The older children are now beginning to ask me to walk out to the island with them: https://en.wikipedia.org/wiki/Cramond_Island but the causeway is in quite poor repair these days and I'm not too sure I would make it there and back. Of course the "old man's curse" might be a limiting factor too as there are no loos out there and always too many people about to risk looking for a bush! All a bit academic now though with all this covid "stuff" It would be nice just to give them all a cuddle again.
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Re: Barrels/Pistons scoring. Salvageable?

Quote Originally Posted by Pugglt Auld Jock View Post
I forgot to ask, if you don't mind saying, where in Maryland are you? My daughter and her husband were based there for nearly 5 years and had a house just outside Leonardtown: https://leonardtown.somd.com/

We spent many happy hours using it as a base to explore all around and do lots of "touristy" things.
Kind regards
Jock
Small world. We live in the Solomons area while I'm stationed here for another couple years. It's a little rural for me, but better than my last station and it'll suffice until retirement.
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Re: Barrels/Pistons scoring. Salvageable?

Quote Originally Posted by JumpJet View Post
Small world. We live in the Solomons area while I'm stationed here for another couple years. It's a little rural for me, but better than my last station and it'll suffice until retirement.
Hmm, Putting "Stationed" and "JumpJet" together could we link "Petuxent" as well? That's where my son in law was.
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