Hi, I have a 1971 just rebored to +80. I am fitting Hepolite (JCC) pistons and the ring set that came with. I believe the rings are Hastings due to seeing a similar looking set from Hastings.I am happy with the quality of all parts. On checking ring gaps I noticed that the oil control 'scaper' rails do not completely conform to the bore. Using a very bright LED lamp behind the ring, I can see that the ends of the ring at the ring gap are holding the ring off the cylinder wall by up to 2 thou for about 90 degrees each side of the gap. I can close this gap with finger pressure on the back of the ring. The top 2 rings are fine and all gaps are ok. The oil ring set is 3 piece - 2 scraper rails and a spacer - the spacer does not exert any radial pressure on the scrapers, just holds them top and bottom of the ring groove.
The bore is good so these scraper rings are not deforming to match the bore circle.
Potentially this will resolve itself on running in, but being at +80 I don't want to accelerate bore wear.
Perhaps I am over worrying - if I hadn't used an LED light behind the rings I would never have noticed !
Any advice ?
The honing is like sandpaper…
- Log in to post comments
I was looking at some tech…
I was looking at some tech stuff in an old 'Automobile Engineer' journal on rings the other day and apparently the manufacturing process is supposed to make sure the outward pressure is uniform all the way round. And that is not all that simple to do, since it means they are not perfectly circular when unstressed. I've never done the light test but it doesn't sound right. Gas pressure helps to keep the compression rings in place on the cylinder walls, but doesn't do anything to assist the oil rings because there are bleed holes behind them into the crank case. Did the rings not come fitted to the pistons? Are they perhaps for +60 instead?
- Log in to post comments
Many thanks John and David…
Many thanks John and David for replies. I have got some more information from Hastings. What I thought was just a spacer for the oil scraper rails is actually meant to also push them out onto the bore as well - Hastings call it an expander - it is a ring of corrugations made from a flat strip with some forms on it to locate the back of the rails and push the rails out. However to do this it needs to be compressed when in the bore. My expander is too short so that when assembled its two ends do not butt together - hence it is not compressed and therefore provides no outward radial force on the rails as is the design intent.
It seems to me that I could stretch out the corrugations to rectify this, but I dont know how much pressure to create - I have started a conversation with Hastings tech department, but to date that are saying do not modify anything - they want me to do a test of friction when assembled with just the oil control pack in the bore - I think this is a waste of time but will comply to keep the dialog going.
Interestingly there is some discussion on Access Norton about people who experienced Hastings oil control rings being too stiff to compress - there are reports by some of trimming ( shortening) the expander , but plenty of others saying this is just wrong - including a well respected engineer, but a link to the definitive study is now not working. It strikes me that since I have the opposite problem ( expander too short) there may have been a move to use shorter expanders.
Ref +60 parts - my set of rings is labeled as +80 and the compression rings and the oil rails all gap correctly, its just the expander that is too short, but I guess it could be incorrectly speced , or mixed up by Hepolite. Attached is some explanation of function from Hastings. They mention using the same expander for different bore sizes provided the inner diameter of the rails is the same - i.e depth of rails changes to change bore size.
- Log in to post comments
From memory the ring…
From memory the ring expander issue on Access Norton was ref the Apex rings made by the real Hepolite factory back in the 80's and Hastings rings. I was one of those back then in the 80's that shortened the Apex expander ring to be able to get the barrel over the piston, still have the bike with the same rings and no oil being burnt. If the ring gaps are right then you have +80 rings.
Some Apex rings for comparison.
https://www.ebay.co.uk/itm/NOS-Apex-Brand-Piston-Rings-Norton-Commando-850cc-R-26730-020-O-S/143453003661?hash=item2166771f8d:g:GE8AAOSwclhd3SmI
- Log in to post comments
Mark - thanks for keeping us…
Mark - thanks for keeping us in this loop. Mercifully my bike only has solid type rings.
If the expander is too short (i.e. I assume it has a bigger end gap than the rails); does it not work properly provided that its end gap is far away from the gaps in the rails? With a solid oil, the 'rails' are part of the same ring so their gaps are in perfect alignment. With separate rails, I imagine they can be placed apart. But maybe they are better placed closely in the same place, with the expanded gap at the opposite side of the piston?
The expander surely does not expand because its end are butted together, does it? Surely it just gives spring force between the back of the ring groove and the back of the rails? So its exact length should not matter. The question is then how did the rails get above and below the expander, rather then where they belong, outside its edges? Unless you put the rails in first and jammed the expander in between, rather than fitting the expander and then adding the rails?
- Log in to post comments
Thanks John - Apex look…
Thanks John - Apex look similar in idea but the corrugations on the apex are 'in and out ' relative to the diameter of the bore whereas the Hasings Flex Vent corrugations run 'up and down' in line with the axis of the bore. Maybe that's the innovation that allows more oil to flow past the expander.
The Hastings Flex Vent Expander is the gold part in the attached pic.
Of interest to me is how much pressure should the expander provide - do you remember how stiff you settled for when you trimmed - relative to a compression ring say ?
At the moment Hastings will not advise me on this, and (apart from being impatient and pig headed and therefore wanting to tweek this myself) I don't think it will be easy to find a supply of better expanders for +80.
Best Regards
Mark
- Log in to post comments
Hi David,Please see my…
Hi David,
Please see my reply to John for a pic of the ring set. The expander needs to butt at its split ends because it is not stiff in the direction of diameter reduction - it doesnt really spring out like a standard ring . Its radial force comes from being butted in a circle bigger than its fitted diameter. Its 'free butted' diameter is shrunk by the oil rails being squeezed into the bore - the expander corrugations all deflect around the circle like a compression spring and thereby its diameter is shrunk and in turn it applies an expanding force to the back of the rails. Note to achieve this the rails sit top and bottom of the expander but the expander also has tabs top and bottom around its circumference that act on the inside diameters of the rails. PS I didn't know any of this yesterday so my little learning might be dangerous !
Best Regards
Mark
- Log in to post comments
Thanks Mark - I now…
Thanks Mark - I now understand. As you say - the Hastings info clearly says that the expander is a compression spring and must be compressed around its circumferential direction to work. So it must be butted when fitted. They say so clearly in your first link. If they don't understand that a gap is no uses, it sounds like the sales department don't know what they are selling! If a general customer played with the expander (or allowed his child to play with the expander) it would almost certainly end up accidentally stretched, and not as in your case apparently compressed and thus too short.
In the earlier times days you could walk into a shop and have a look inside another packet (I could have done so locally); but that's not so easy nowadays.
- Log in to post comments
I fitted that ring set in…
I fitted that ring set in 1982, so memory is hazy but I took enough off the length until the tool I as using to compress the rings enough so the barrel would go over the pistons showed no gap between it and the piston. The steel rings when not compressed by the tool were still larger than the piston and the expander ring ends were touching..
- Log in to post comments
Update for anyone interested…
Update for anyone interested.
My discussions with Hastings concluded that my 'expanders' were too short to expand the oil control rails and make them conform to the bore - hence the gap issue on the rails. ( incidentally Alan I did fit the 3 piece oil assembly rings alone on the piston and there was no difference - i.e 1 or 2 thou gap in places on each rail) .
Hastings advised that I needed a new oil rail assembly comprising rails and expander. I am in the process of sourcing these through UK agents. When installed the expander will be compressed about 25 thou on diameter which is about 80 thou on circumference.
Why was my expander too short ? I contacted Wassell who are the source of Hepolite piston kits. They advised that they had stopped supplying +80s because the demand was too low to justify the costs. They were not aware of any problems. Seems my pistons were old stock when I got them, maybe someone somewhere had mixed parts up for some reason. I'll be talking more to the seller.
I will post a conclusion once new rings sourced.
- Log in to post comments
The honing is like sandpaper, its purpose is to grind away at the rings and make them take the shape of the bore. The honing itself will also smoothen out as the rings wear it away. For cast iron rings you want a rough finish, a finer finish for steel rings as they are supposed to be a closer fit. None of this tells you if your particular rings in your freshly honed bore will work, only running it will but at least you know the process and if it does burn oil the oil control rings would be the first suspect. I would install the rings in a dry bore, dab of oil on front and back of pistons. Before you attempt the first start be in a position so you can ride it, idle it only long enough to get it timed. when you are on the road give it short bursts of full throttle so the compression gases get behind the rings and force them to wear against the honing.