Dommie 99 bore dimensions.

Hi Ron, how many fins on your barrel?, Thats a strange size. If the pistons and bore are within limits you could get the spigots removed and fit rings to the head recess. Or not bother with them as it seems motors run ok without. Alternatively if the pistons are ok get new liners to suit and fit new piston rings.Or if the top of the liners are damaged ,get them pressed a bit higher up the barrel before you get them trimmed.

New sleeves will need boring to suit new or reused pistons. It would be worth checking the pistons for reuse as they are often fine. The bore size is odd, perhaps someone was not happy to bore for liners that left little of the orriginal cylinders strength and so bored and fitted undersize liners and used non std pistons, any numbers on the pistons?? could be from another bike ,not Necessarily Norton!!. Seems like it could be rebored for 88 Std pistons if you were prepared to accept an annulus. Or get the liners moved up and trimmed , Some out of box thinking needed!!.

Ron. It may be as well to check the zero, or accuracy, of the digital display on your calipers. Ignoring the digital display, look at the alignment of the left hand leg of the caliper where it enters the bore, to the measurement above it, and it aligns approximately with 61mm. I have the same set of calipers, and when I do that with mine, the digital, correct measurement displayed is 69mm. That would equate to a + 0.040" oversize, a measurement at which the liners become so thin, like yours, that the spigots start cracking. Given your measurement of 63.66mm would give a capacity, from an 82mm stroke, of 522cc; pretty unlikely, to say the least! If so, why would the liners be so thin?

To put it another way, if you read off the markings on the calipers, it is showing 68mm or thereabouts.

No worries Ron, we all make mistakes! So that appears to make it + 0.030". Because of the broken spigot, and the cracking entering the bore, it clearly needs a re-sleeve. I would not re-use those pistons, as it would mean boring the new liner to + 0.030"; not a good idea. Save them for 2 x rebores hence (unlikely!), or flog them on e-bay.

Keep us posted!

Ian

RGM lists sleeves. Some of them have a top spigot. Is that intended by the maker to be fully recessed, or is to replace the old broken spigot?

And incidentally - about piston prices - last time I was looking I found some sites to be very ambiguous about whether the price was for one or for the pair.

Previously ron_tomkins wrote:

Just took the head off to be greeted with the spigots on the liners showing serious peripheral cracks at the level of the top of the top piston ring when at tdc. This has lead me down the path of researching replacement liners and pistons. Having read pretty much every post on the subject, I now have more questions than answers. Can anybody offer any guidance on the following: 1. The manual says that the bore size for a 99 is 68mm. Mine measure 63.66. 2. Plan A is to make a liner puller and prepare to install new liners but the pistons look good so should I be thinking of installing liners to suit the pistons or go back to standard and fork out for new pistons. 3. If I go for the back to standard option, how do I decide what pistons to use. Norvil standard pistons are in the order of £220 a pair yet they list Std. Hepolites for £84. That's one hell of a difference. 4. Whether I go for oversize liners or standard liners, do they need machining after being pressed in?

Hello Nortons original pistons where BHB and your bore is 68.66 not 63.66 only navigators are 63mm not dominators the model 88 are 66,mm the model 99 are 68mm So your on maximum 60 thou over size the best after market pistons are JP pistons form Thornton of shrewsbury see there website best engineers for rebores are SEP, see there website, Ps try not to fit bricks called Gardini Motor pistons there well made but heavy witch will blow your balance factor or try get a set of Omega pistons yours anna j

Previously anna jeannette Dixon wrote:

Hello Nortons original pistons where BHB and your bore is 68.66 not 63.66 only navigators are 63mm not dominators the model 88 are 66,mm the model 99 are 68mm So your on maximum 60 thou over size the best after market pistons are JP pistons form Thornton of shrewsbury see there website best engineers for rebores are SEP, see there website, Ps try not to fit bricks called Gardini Motor pistons there well made but heavy witch will blow your balance factor or try get a set of Omega pistons yours anna j

Just to contradict Anna, when I had my 650SS re-sleeved back to standard not too long ago the original pistons supplied were JP which were miles too heavy by around 74 grammes each. I replaced them with Gandini pistons, which is what I assume Anna is referring to, and they were much better and reduced the vibration to normal levels. Plus I was having great problems running in the JP pistons with tremendous oil consumption and much smoke. Absolutely no problem with the Gandinis from the start and oil consumption now is negligible.

Lance. Do you recall the weight difference between the Gandinis and your original ones? What would be relevant to this is what pistons you had prior to the resleeve, as they were no doubt replacements of either + 0.040" or maybe 0.060" even?

I ask because I am bracing myself for a resleeve of my 650SS also.

Ian

Previously Lance Crossley wrote:

Previously anna jeannette Dixon wrote:

Hello Nortons original pistons where BHB and your bore is 68.66 not 63.66 only navigators are 63mm not dominators the model 88 are 66,mm the model 99 are 68mm So your on maximum 60 thou over size the best after market pistons are JP pistons form Thornton of shrewsbury see there website best engineers for rebores are SEP, see there website, Ps try not to fit bricks called Gardini Motor pistons there well made but heavy witch will blow your balance factor or try get a set of Omega pistons yours anna j

Just to contradict Anna, when I had my 650SS re-sleeved back to standard not too long ago the original pistons supplied were JP which were miles too heavy by around 74 grammes each. I replaced them with Gandini pistons, which is what I assume Anna is referring to, and they were much better and reduced the vibration to normal levels. Plus I was having great problems running in the JP pistons with tremendous oil consumption and much smoke. Absolutely no problem with the Gandinis from the start and oil consumption now is negligible.

Hello Now I up my hands up here some conflicting information has been coming my way I did think my self that Italians made nice lightweightparts So New Information comes to light, tried and tested I am running on the Original BHB witch are good the same pistons went into the R/R Merlin and they were reliable they had to be, my uncle Burt made Cylinder heads for Rolls Royce Merlins I have his Mercer Clocking dial gauges set with magnetic stands over 80 years old now but still works fine, and Omega is now making pistons for Nortons and thank you very much for your comments they were appreciated yours anna j

So Gandini pistons are ok, are they? It would be good to know weights, to compare with the original pistons, if that information is available. Shame suppliers don't provide that information. It would seem that, with a change of pistons, the crank/rod/piston assembly should be re-balanced to the original factory balance factor. One could end up with a very unpleasant engine otherwise.

There are quite a few comments on piston weights back here:

https://www.nortonownersclub.org/noc-chat/technical2-heavy-twins-forum/948381324?b_start=0#855280036

Previously ian_cordes wrote:

Lance. Do you recall the weight difference between the Gandinis and your original ones? What would be relevant to this is what pistons you had prior to the resleeve, as they were no doubt replacements of either + 0.040" or maybe 0.060" even?

I ask because I am bracing myself for a resleeve of my 650SS also.

Ian

Hi, Ian.

My original pistons, make unknown, including pins, circlips and rings and ignoring a few fractions were 309g each, and these were plus 60 thou. The JP pistons (standard bore), circlips and rings were 381g each and the Gandini (standard again), circlips and rings were 285g. I got the Gandini pistons from RGM, who give the weight on their website. Whilst not an exact match in weight for the originals they are much closer than the JPs and vibration is around what it was whereas the JP pistons were unpleasant, even after having around 30g removed from each piston. I could have had the crank re-balanced instead but didn't want to take the engine right down so opted to pay again for the Gandini pistons. The original pistons and crank had been balanced by RGM some years ago. Total cost, if you're interested, including new valves and guides, liners, JP pistons complete plus labour came to £650, somewhat more than I'd been hoping for! Plus the cost of the Gandini pistons at around £220. Just as well I'd received a lump sum for retirement from my employer to put towards it!

Good luck if you decide to go ahead.

Thanks for that Lance.

Ian

Sorry story...

RGM illustrate liners with a top shoulder. Maybe the ones you have are really for a later engine with no spigots?

However my 1963 is lined inside the spigot. There is a thin cast iron upstand visible around the liner. Just visible. So my liners must be plain cylinders also.

I have never had a Norton with a liner. As far as I am aware Norton only ever used liners on alloy cylinders and a top flange is a good feature to hold the liner in place. The motor industry has used unflanged liners in water cooled steel cylinders without issue. I have seen Norton twins cylinders bored for liners leaving very fragile spigots and weak lower parts. Seems to me that its asking for trouble. 99 barrels appear the worst for this. A flanged liner in a 99 must leave the cylinders in a weak state due to the need to clear away the existing spigot. Its time we had some new cylinders. An alternative could be some undersized pistons fitted in a liner that would press into cylinders that are just over 40 thou worn ,so retaining the strength of the orriginal ? 88 pistons in a linered 99 barrel??.

So why does RGM list liners with top flanges? Surely that flange would provide an excellent spigot - better than inserting loose rings? At one time I was toying with the idea of putting some 99 pistons into my 88, but it is already lined and the OD of the liner is so close to the ID of a 99 that there's no way they could fit unless it was lined even further out!

Yes David, The RGM liner could if machined right do that job ,but I wonder if its Not intended for the early motors with the spigots. My idea of using 88 pistons in a 99 is to avoid thin weak barrels ,does not help the 88 .

On the 88 and 99 engines the spigot has to sit inside the same size cylinder head recess. Now if you think about this point it confirms that the 88 and 99 both originally had the same the same cylinder O.D. The 99 barrels being bored out more for the larger pistons and the 88 barrel being reduced in height to match the smaller crankshaft stroke.

As a rule.....Model 7/88 barrels can be bored out to plus 80 and even plus 100 thou using 99 pistons as replacements. Though the new capacity will be a little strange.

In some of the early Model 7 maintenance books the max rebore size is quoted as plus 40.

Many 99 owners have discovered it was not a wise move to go to plus 60 thou. With broken spigots occuring at either the top, bottom or both ends of the barrel. Broken top spigots are not generally a problem as long as the damage does not reach down into the bore and give the top ring some grief. Just get the remains ground off and use the barrel as unspigotted. The head gasket will cope with this unless somebody has fitted very high compression pistons.

Thanks for that, Phil. That means I could bore the 88 out to fit a 99 sleeve, and then use the 99 standard pistons (n.o.s.) I have. They weigh the same as my old pistons. But the spigot would still nearly vanish - in fact I'm sure it would. I've not compared the OD of the spigot on the 88 with the ID of the recess in the head. But if the head is the same as (say) 650S, there must be quite a lot of space outside my spigots. And indeed over them! If gases can get over and behind them, there can't be a lot of point to have them - apart from some unnecessary protection to the gasket edges from engine flames.

I'm not taking the head off just for fun to measure up. If ever I do, I might try out an ultrasound thickness probe to check first.

So that leaves Ron with his issue - it sounds like the bottom of his bore had a step back in to the original size - maybe to stop the liner from slipping down into the crank case? Probably the manufacturers never originally considered that old engines might be re-lined twice? A shoulder at the top would do the same job, and provide a spigot...like these?

https://www.rgmnorton.co.uk/csi/1245184/f/pdf/cylinder_liner_drawing.pdf

I see these do have a step in at the bottom. Just to complicate things. But if you have a head with no spigot recess, the top spigot on the liner would need to be recessed I assume?

Hope it all works out, Ron.

I'd just like to correct my previous mail. I've just dug out a picture of the top of my 88SS barrel. As you can see, the spigots on the 88 were much wider than the 99. Almost certainly the same OD. So Norton created the fragile spigots when they first bored out to make the 600cc bikes, because the OD of the spigot must have remained the same in order to fit the head recess. So maybe that's why the later bikes lost the spigot. It saved them from changing the head recess to fit each size of bike when they were making 500 and 600 and 750 at the same time in the early 60's.

Just for fun, the picture also shows a hole in the piston!

(Sorrt for two pics: can't seem to delete..)