Navigator Pistons

Probably a silly question,   why change the rings?.The piston does not show signs of blowby. Are the bores rusty?.

I once owned Navigator DEL28C. Registered with Dorchester police in 1965, one of two ordered for senior police transport to incidents. 15,000miles and good order when I bought it. I really liked it.

While I had the bike in 1969 the bike was stolen, chased by the police, bike and the villain pulled out of a hedge in a council estate. I think the twist grip got jammed fully open at the crash. Quite an experience listening to the chase live at the radio room of Chicheseter police HQ.

Thereafter the bike always smoked a bit on the right. 18 months later, after a run to blow the cobwebs, the right hand piston crown left the rest of the piston.

The build was a late spigot-less one like yours Nick.

My advice to you would be to restore as you found it. So many of these bikes were ruined by unnecessary maintenance. Try very hard to get another composite one piece gasket like you took off. Old Navigator gasket sets surface on eBay with the composite head gasket included.

You should see the piston manufacturer markings (AE ?) inside the piston, part of the forging/casting. Not on the top. I believe in mid 60's Hepworth, later Hepworth and Grandage, were part of the AE group. We still have AE turbine components in Bradford, who in the '70's were Hepworth and Grandage, making forged gas turbine blades. More profitable than motorbike pistons.

Put your pistons back as you found them. Unlike Robert I'd recommend you buy new piston rings . Also new retaining rings. Did you mark L/R and front/back on the pistons as you removed them? If not, anther good reason to put in new rings. Your rings look like the standard ring widths.

It is so annoying to re-use piston rings and find your bike becomes a smoker. I know.

All the best

Peter

I believe DEL28C is still around and looking much better than when I had it. About 10 years ago the proud owner's photo showed it had lost all it's patina (My blue and black hammerite over the rusty bits) and been fully civilianised. (Lost it's tank with radio cut-out. A4 size and very useful for maps and stuff.)

Back in the days when rings and oversize pistons /spare barrels were  readilly availiable  I would often pop in some new rings  without a qualm . Sometimes without even a hone ,just a good rough up with some emery and a scrape round the top to remove any step.Hard daily use and  cheap oil meant that running in did not take too long. Some new rings are now so hard that  a good hone or rebore is needed to bed them in if you are to avoid  a long  proccess . Our Atlas is now running well with a hone and new rings on the old pistons , the old rings were ruined by my lad never changing the oil resulting in heavy  wear ,ring flutter and oil pumping. Took a while to find some suitable rings. All  unnecessary work with good maintenance !.

...and good luck finding new circlips...as Bernal Osborne wrote in my copy of Modern Motorcycle Maintenance ... "avoid unnecessary fettling!!!!:

If its not smoking now plus the ring gaps are not excessive then put the old rings back in, you save a hone and the running in period.

It does seem that the lightweights are  poorly served with  pistons and cylinders , The quality of replacements has been discussed  in previous  posts . If there is any hiccup with any  new rings and you are then  faced with a rebore and new O/S pistons your bike could be in a basket  for a long  time . Take extra care  with your good  orriginal stuff  . You are lucky to have it.

Not sure why David thinks these will be a problem.

In the NOC shop part number 21581.

Or if you want something the same as before, this pack of 5 from Simply Bearings should do the job. Check the dimensions yourself but I think these will do. 

RSR14MM Round Snap Ring 14mm Nominal Shaft Diameters Simply Bearings Ltd

Peter

Hi Nick,

Edmunds Walker were not taken into the AE group of companies until 1968. Hepworth was one of the three companies in at the start of Associated Engineering in 1947, along with Wellworthy Piston rings and British Piston Ring.  Hepolite was a brand name of AE in the 60's. I don't know if EW made pistons, but AE already had a piston manufacturer in the family.

You seem to have the living evidence that Navigator pistons came in Electra style, with oil holes under the wide ring groove.

The club have an old print of Norton drawing 24708. Electra piston. Sadly I don't know of any Navigator piston print.

Drawing date 27/7/62 and this print to toolroom at Plumstead 1/3/63.

Some of the notes catch my eye.

"Based on H&G Drg No. X16025 but increased diameter"

"See later H&G piston Drg X16104 drawn 20/9/62"

"Use Navigator G P". "H&G request different gudgeon pin"

"440cc, CR 8.25:1. Stroke 58mm. Max RPM 7000, Est max power 24 BHP. Est explosion pressure 1,100 psi."

All this suggests that H&G were the design authority for the piston assembly and the Norton drawing was produced for inspection purposes. The drawing shows the piston with 8 oil holes in and 6 below the lower ring groove. Solid skirt.

Was X16025 a Navigator piston design similar to Electra?

Was X16104 a later drawing of this Navigator piston? Did one of these H&G designs go into production?

Norton may have slid a change of piston design into Navigator production without changing the part number. No parts lists and build schedules to alter and it could be seen as interchangeable with split skirt design. I don't suppose Navigator documentation had priority in the AMC design office. I'm sure it would have been done to address piston issues.

Any AE numbers like these above cast/forged into the piston inner surface?

Fascinating.

Peter

Fascinating indeed, Peter - giving much food for thought. 

24708 is indeed Norton's P/N for the Electra piston (I forget the H&G P/N now alas) but those dimensions are interesting:

Production Electras were 66 x 56 mm, yielding a swept volume of 383.2 cc

Joe Berliner's prototypes were 66 x 58 mm, giving 396.9 cc

440 cc, 58 mm stroke imply a bore of 69.5 mm! Hard if not impossible to achieve without changing the piston / rod / journal spacing in my view. And cost would doubtless have precluded that.

Concur absolutely that H&G were the design authority, which is why it is always their P/N and not Norton's which was stamped on the crown. [Applies to all five known types of lightweight piston, and I suspect to the big twins too.]

Looking at the squared off (unchamfered) gudgeon pin bores, I am unable to attribute NIck's oddball pistons to H&G, who knew better than that. I think it far more likely that they are aftermarket pistons from one such as JP Pistons of Australia. The '63 xxx' stamping on the crown also suggests the use of a 'universal' 63 mm blank which has been finish machined to the required dimensions. As you say to Nick, inspection of the inside of the skirt will confirm that.

If they are aftermarket items, they are likely to be heavier - the JPs that I bought as pares for my Electra, but could never bring myself to fit, certainly were. It would be worth checking ...

Even so, it is interesting to ponder whether H&G might have been considering a change to the 'pepper pot drilled' design as adopted on the Electra? Even the later Navi pistons (15418) would crack eventually with spirited riding, though they last much better than the originals 

400 cc the capacity on Electra piston drawing 24708. My error. 

You make a great contribution on the lightweight piston story. Told as someone who seems to have a fair bit of background - I suspect. 

Thanks Peter

Some good stuff written above – thanks Peter (& Roger)!!

Nicks pistons at the top of the thread:

The piston on the left is unusual, and looks marginally taller than the (usual) piston on the right, and you can see that it sticks up a little in his photo of the barrel. The 63 xxx makes it look like a standard 63mm piston, as Peter suggests.

Bear in mind, that spigotless barrels (introduced around Oct '63) were actually 2mm taller than spigotted barrels – as the spigots had to be machined. You will notice (although Nick does not show us) that the matching heads will have had 2mm skimmed off them – like Electra heads.

My Navi is number 106840 and uses spigotted heads (I've owned her since 1972) and I know that Navi 106979 (only 150 numbers after mine) defo had spigotless barrels from new. And, as it happens, I know Nicks bike is only about 50 numbers up from mine – so was made around the same time as well! So we near enough know when the change occurred.

If Nick uses his 'special' pistons, he will have two advantages over me: 1) He will have slightly higher compression, and 2) The top of his piston is less likely to come off!

The Jury, however, is out on circlips. The snap rings Peter shows us RSR14MM Round Snap Ring 14mm Nominal Shaft Diameters Simply Bearings Ltd are for fitting to shafts, with a groove. Are they really suited to fitting in an outer groove?

There is a secondary problem in using snap rings as circlips - their removal!

I just copied a Picture off Andover Nortons Website for you, showing a Commando piston using snap rings - note the cutouts to enable removal of said snap rings.

My experience with Navigator pistons, when I was rebuilding my 1963 Navigator engine the rings were damaged due to the bike coming to me in a number of boxes (a real basket case) the bore and piston are in good condition at 0.020” oversize and the piston is of the same type as shown in Nicholas Clark's photos, I ordered a new set of rings from NOC and the size was completely out with the rings thickness being to thin, With the help of Brian North (engine reconditioner in Cardiff) we identified that “Cords” rings had been fitted, Brian has a good stock of “Cords” rings and we found that rings for a "1936 Ford Utility V8 Vedette" are very close to the required size. All I needed todo was widen the groove for one of the rings and deepen the Oil ring groove to give the correct internal radial clearance (ring to piston) on both pistons, all machining done on my Myford Lathe at home. Bike as now done over 200 miles with the first 100 using running in oil. I have a cartridge oil filter fitted which I plan to change at 500 miles.

As for the pictures I will have to load them one at a time because the 5 MB limit!  

Download Irfanview, open up the picture and then select save, under 'set size as' put in either 0.5mb or 1 mb and then save, agree to overwrite or rename it as say name compressed. Now you have smaller pics you can post.

https://www.irfanview.com/

I had hoped to unearth the photos of the JP Electra pistons that I passed on, unused ... but seemingly that was three computers ago, and all I have retained is the last two! So no joy, sorry.

I will still have < somewhere > my record of their weight, but I won't be able to conjure that up quickly, however. I do however recall clearly that they were more than 20g overweight, and possibly as much as 30g.

I have just measured a NOS STD H&G piston (15418) at 242g with gudgeon in and rings but not circlips (none readily to hand).

As a by-the-by, I once bought and used a pair of later-type Navi pistons (+010) bearing P/N 15625 rather than 15418, and likewise branded AE. No idea what the difference is, they were visually identical. The PN was stamped on the crown and cast into the skirt in usual fashion. Most that I have encountered in 40+ years of Navi ownership are 15418 though, other than the fragile 15110 originals (of which few now survive).

Best regards, Roger

Hi Nick.

Sounds like the full strip. You don't need to remove the timing pinion from the crank unless you are changing the r/h ball main. Every other job like splitting crankcases, removing conrods etc can be done.  After splitting the c/cases, a blowtorch round the ball bearing housing will expand the alloy and gravity will pull the crank and bearing free. No seal to ruin in that area.

Leave the camshafts in the crankcase if you prefer, but I do recommend removing the intermediate pinion so that the cam lobes are easily positioned for crankcase separation and assembly.

Some extractors from the regular suppliers have jaws that are not flat to follow the sides of the triangular spacer. The radius they put in massively reduces the pulling potential. You could reshape carefully with a file.

I hope you achieve what you are doing. 

Roger may have better advice. A true expert.

Peter

May I worthy of such praise, Peter! - but I can add nothing useful to your fine contribution. I was obviously lucky with my extractor, as it has always worked well for me. I concur though that the prongs MUST conform to the flat faces of the triangular plate, given the minimal overlap.

Back to pistons: Yes, I was quoting H&G part numbers, as marked on them. The format may be the same as Norton used, but I am aware of no unique-to-lightweight Norton P/Ns below 20xxx, and those unique to the Navi seem to start at 22xxx. Both my 1961/1962 and 1964 Parts Lists cite the same 23972 ID that you noted in yours for the complete piston assembly (standard size). 

As for circlips, I have only ever encountered traditional circlips on H&G pistons for the Jubilee, Navigator and Electra, but I do not recall what was supplied with the JP aftermarket items, alas.

Wire clips work well enough for other makers though, albeit that some had turned in ends on theirs, for ease of removal.

Nick, you are using the correct special-to-type half time pinion extractor, I take it, and not a general purpose three jaw puller? The proper tool has an outer sleeve that prevents the legs splaying out as the tension is applied.

Roger

My general purpose pinion extractor came with jaws for Triumph or BSA pinions but took the NOC spare jaws. I found that I had to loosen the outer sleeve and pull the jaws behind the pinion with cable ties.

As a last resort  you could use a mini grinder and chisel  to split the pinion , assuming you can get a spare.