Dominator 88

Andymann · May 25, 2020

Mike40M said:
A quick check in the spare parts list for 1959 88 and 99.
Crankshaft different stroke, pushrods different length, barrels and pistons different. The rest seems to be the same. Might have missed something.
So to be certain, you have to measure stroke.
It could be that PO found that max overbore .060 was not enough so he had it rebored to 68mm and threw in 99 pistons.

I'm thinking that is most likely what has happened. I'm going to to a proper measure of the stroke tonight though - just to confirm!

dynodave · May 25, 2020

FWIW
folks seem to be confused or.... so used to slang type lack of clarity
12, 12-2, 14, 18, 20, 20M3, 20M3S are the engine series. which stopped within commando

7, 88 wide and slim line, 99, 650, atlas, commando are BIKE models "with a association" to a specific engine.
welcome to the clear as mud confusion.
I'm not trying to justify it , but let you know it exists...

Triton Thrasher · May 25, 2020

Andymann said:
Well I figured I would just measure the conrod length, but it looks like the 500 and the 600 shared the same rods. So how did they increase the stroke?

The stroke is the distance the piston travels, from top to bottom of the cylinder. Measure that.

A longer conrod does not change the stroke.

A longer stroke requires the centre of the big end journal to be a greater distance from the crankshaft centre line.

t ingermanson · May 25, 2020

There is also a possibility of a 99/650 barrel on an 88 case. Without the change of crankshaft (stroke), that would lead to very low compression ratio. 99/650 barrels have 9 fins, the 88 will have 8 fins. I don't know if it would even run with that low of a cr though.

Andymann · May 26, 2020

So just to make things even more confusing - measured the crankshaft big-end bearing journal diameter and they measure 1.5". My manual tells me that the 500 crank has 1.5" diameter journals.

norton bob · May 26, 2020

The 88 and 99 used the same conrods and heads , the big ends were both 1.5" but the 99 had a longer throw on the crank which needed a taller barrel and pushrods. The 650 had an even longer stroke ,bigger big ends and different (shorter?) rods and can with a bit of work use the 99 barrels which may not really be strong enough for thrashing a 650. The 650 crank does not have quite enough room in the otherwise nearly identical88/99 cases so some extra space was cast in the back to make the 650. Rob Sewell raced an 88 with a 750 capacity after some surgery .The 88 barrels start off with more meat in them than the 99 so can be bored to take some 99 pistons instead of liners (maybe a little cut off the long skirts).Short skirt 650 pistons fit better. Piston pin tolerances can be an issue with some pistons and old rods/ pins. You also have to watch out for rod clearance at the bottom of barrels and case mouth castings. 750 barrels are something else and need serious work to fit the earlier motors. Not worth the bother unless your name is Rob.

Andymann · May 26, 2020

Well this now is getting really fun - the barrel has 8 fins so it's definitely then an 88 Barrel correct? But the bore is 68mm so it has definitely been overbored to take 600 pistons.
I then measured the distance from the center of the crank to the center of the big end - that measures 41mm - so the total throw on the crank would be 82mm - which in my mind makes it a 600 crank.

How everything fits together without spacers is anyones guess - but it did run, so I'm going to leave it be. Anyway, I have new rings, new undersize shells, and a new gasket set so it's off to the engineering shop and then reassembly!

Mike40M · May 26, 2020

Interesting. Anybody who can confirm the number of fins? Just to be certain.
I think you shall check clearance between piston and head and valves when assembling. Especially if not a standard cam.

Andymann · May 26, 2020

To top it all off I thought the head gasket looked a bit odd so I measured the diameter of the gasket and it is 74mm - so probably a 750 head gasket. Given my bore is 68mm that means a 3mm wide gap of 1.25mm height around the combustion chamber. That's roughly 0.84cc extra in the combustion chamber. No wonder the CR felt so low....

t ingermanson · May 26, 2020

Whew! Talk about a bitsa!

You have no spigots on the top of the barrel then? A "spigot" is a rim around the top of the bore, cast into the iron of the barrel. They were phased out on later models. The matching heads had mating sockets to accept the spigots. There are aluminum rings available to fit into the sockets to return to the desired cr, if the head is spigotted and the barrel not. They have received mixed reviews.

I think @Mike40M is very correct about checking your valve/piston clearances. I don't see how a 99 longer stroke crank in an 88 barrel would work without nonstandard pistons, and/or a very thick head gasket. However, if there's damage to be done, since it's been run, the damage is done. This scenario would have been hard to foresee.

Pic of Model 7 and Mercury barrels and heads next to each other. While neither is an 88 or 99, they have the same barrel height and quantity of fins.

8 fins on the left and 9 on the right.

All this said, it doesn't quite add up that a long stroke crank in a short stroke barrel equals low compression, with all original working components otherwise, incorrect head gasket included.

Andymann · May 27, 2020

I'll be honest I really have no idea. But rest assured, when the barrel is on again, I will recheck the stroke and revert back to everyone!

Now one more pressing issue - my conrod big-end eye is slightly oval, so I need to have them re-sized. Does anyone here perhaps know what the unworn diameter should be - my lower limit is 40.77 which is a really odd size - 1 39/64"

Mike40M · May 27, 2020

Sorry, not found any source for big end dimension nor ovality. Just guessing, maybe 1.6".
Neither the Norton Maintenance Manual nor the Haynes mention it.
How are the small end bushings?
I suggest that you get an estimate on cost for machining, compared to a pair of new conrods. RGM can supply.

Andymann · May 27, 2020

Hi Mike - thanks! - I had a quick look and while I would love to, I'm afraid our currency exchange rate (which was high before Corona) has now collapsed with our economy. So this is making purchasing parts from the UK a very selective process - couple that with our Postal Service which is shocking means any parts have to be couriered out to SA. We are now 22ZAR to 1GBP and with DHL costs included a set of rods will cost me upwards of 300GBP. In SA terms that is the same as what the monthly repayment is on my RAV SUV!

Triton Thrasher · May 27, 2020

A small end eye in an alloy rod, distorted into an oval shape can indicate that it’s going to break, in the not too distant future.

t ingermanson · May 27, 2020

Machining to "save" a 50+ year old distorted conrod is bad news and false economy. These parts take an absolute beating, and one that's already beyond its elastic limit is asking for a holed case, at the very least. The distortion is a sign of past trauma and as a loud warning as an inanimate part can make.

New ones are expensive, but there are other options. The Norton Owners Club site may have something within their spares, or perhaps a "Wanted" ad here on this site may turn up something that would be much cheaper and you'd end up with a better, if not ideal, rod. I avoid Ebay for things like conrods.

As I'm sure you know, bargain vintage motorcycles need one of two things thrown at them in copious amounts: money or patience. I have little money, so I shoot for the latter.

Mike40M · May 27, 2020

Both patience AND money.

norton bob · May 27, 2020

Any 99/88 rods the club have are SH with unknown history. I bought one many years ago to replace a marked one ,the club one was no better . Its in the outside Dunny with other stuff !.

t ingermanson · May 27, 2020

Mike40M said:
Both patience AND money.

I'm trying to sound optimistic! HA!

The situation on the NOC parts is good to know. I need some 88 rods as well, and have resigned myself to having to spring for the Thunder or JS rods. I have some in good "measurable" shape, but it's the unknown that puts me off of them.

Norton Dominator parts are very thin on the ground in the States, so being able to measure something in person is almost unheard of. I'm sure it's the same in SA, and probably the reason for the mismatch to begin with.

dynodave · May 27, 2020

1.6053-1.6062 is the range of about the 10 rods I have. This surveyed was done at the request of holland norton works.

norton bob · May 27, 2020

That sounds like enough to take away most of the running clearance,and give a tight assembly when a new set of shells fitted to a used crank. Its what happened to me 25 years ago with my 99.

Dominator 88

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