Dominator 88

Hi All - just a word of thanks for all the information offered here. Really appreciate it, and of course all the opinions!

If I was going to use the bike regularly, I would most certainly have invested the cash and gone for new rods. However in this case, the bike was bought with no licensing documents (it's still legal in SA to purchase a motorcycle without them), and is so far from being roadworthy that the chances of me ever using it legally on the road are very slim. I'm also not a racer so I won't be taking it out on the track. At the very best, I will probably be taking it down (very discreetly) to the local coffee shop once or twice a month. I bought it because I felt it just deserved to be saved from being sold as scrap, and also because I have never worked on a Norton before so was keen to try. And boy have I certainly learnt a lot - all thanks to everyone here on this thread. What's really been interesting for me having worked on this engine are the diverse Engineering paths taken between Norton and Velocette - one might have assumed that like the UJM's of the 80's the British bikes of the 50's would have followed similar design principles - one only needs to compare the Norton clutch (which I am certain Yamaha copied on their DT's) to the clutch on my 1957 Venom to realize this is most certainly not the case! As an aside, I might not have mentioned in my intro that I worked for Yamaha for many years as a Product and Development Manager so know quite a lot about the various Yamaha models - my turn to offer a bit of advice - Yamaha TDM850/TRX850 Clutch springs are a perfect fit for a Norton Dominator 88 clutch!

Anyway, back to the rods - we decided on a root diameter on the bigend eyes (without shells) of 40.77mm which ties in very closely with the 1.6053" (40.77462) which dynodave has given. The rods are now at the Engineering firm being sorted. Once they have returned, I will bolt them together with the new shells and mic up the new diameter, which will then be given back to the Engineering firm to grind the crank.

One thing I cant find in my manual is the crank to bigend clearance - all they mention is that "while a small amount of side play is permissible, there should be no play whatsoever in the vertical direction". Is there an official Norton spec, or do i just use the norm for white metal bearings?

Make sure that whoever grinds the crank journals is aware of the.090” radius in the corners.

triumph2 said:

Make sure that whoever grinds the crank journals is aware of the.090” radius in the corners.

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Thanks - I did find this in my manual - although they say 0.095". I doubt if the 0.01" will be that critical though. Hope not!

Andymann said:

If I was going to use the bike regularly, I would most certainly have invested the cash and gone for new rods. However in this case, the bike was bought with no licensing documents (it's still legal in SA to purchase a motorcycle without them), and is so far from being roadworthy that the chances of me ever using it legally on the road are very slim. I'm also not a racer so I won't be taking it out on the track. At the very best, I will probably be taking it down (very discreetly) to the local coffee shop once or twice a month. I bought it because I felt it just deserved to be saved from being sold as scrap, and also because I have never worked on a Norton before so was keen to try.

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Makes perfect sense to build a motor back up with questionable parts, so you can score points back at the coffee shop a couple times a month. Who cares about the next owner who thinks they just bought a race bike and take 'er out to see how fast she goes? Right?

I'm all in favor of doing whatever you want to your own motorbike, but putting known bad rods in a bike is negligent.

I have a memory that clearance should be one and a half thou, will try to find the data. I do know that a bit more clearance does not seem to be a problem ,still going 25 years later when I thought it was scrap back then. Too little clearance ie not free to fall under own weight is no good at all.

t ingermanson said:

Makes perfect sense to build a motor back up with questionable parts, so you can score points back at the coffee shop a couple times a month. Who cares about the next owner who thinks they just bought a race bike and take 'er out to see how fast she goes? Right?

I'm all in favor of doing whatever you want to your own motorbike, but putting known bad rods in a bike is negligent.

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I think it's about perspective - The rods are in no way bad. The maximum ovality measured was 0.002" measured N-S which is expected given that's where the major forces occur. Negligent would be if I ignored that, and just put in new shells. I have taken 0.001" off the flat surface of the end-cap, and similarly off the rod, and then had the rod-eyes re-machined to perfectly round - in this case 40.77mm dia to fit the new shells. The small-ends are well within the tolerance required so I have left them alone. I don't believe that any of this will increase the risk of a rod failure, beyond the risk which was already present from a 65yo component. Assuming of course that they are OEM - which I sincerely doubt given the mix and match of components already found in this engine.

Nice job. It's not the 65 years, more the miles and how high rpm's that counts. 2 thou ovality indicates that it has lived a not too hard life.

Might have to work a little on the rod nicks that locate the shells.

dynodave said:

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.

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Eventual reply here, found it... http://atlanticgreen.com/images/1.5conroddimensions.tif

dynodave said:

Eventual reply here, found it... http://atlanticgreen.com/images/1.5conroddimensions.tif

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Hi Dave,
Offtopic: This drawing sparked my curiosity. Why would the design office of AMC redraw a drawing for a part no longer in production (?), at a critical time for AMC (spring of 1966)? One would think they had more urgent business to attend to.
The rods were not used in the Navigator and Electra engines, no?

-Knut

Andymann said:

I think it's about perspective - The rods are in no way bad. I have taken 0.001" off the flat surface of the end-cap, and similarly off the rod, and then had the rod-eyes re-machined to perfectly round - in this case 40.77mm dia to fit the new shells.

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It's a common procedure. We do the same to Matchless twins which are very suspectible to big end ovality. The downside is your CR will be a little lower due to shortening the rods, unless you mill the barrel deck and/or head.

-Knut

Re oil pressure and excessive oil , IMO someone has fitted a 6 start, double speed oil pump mod, either that or you have a partial blockage on the return oil pipe somewhere. I fitted one to my 1965 Atlas, but I went the whole hog of upgrading to the 1966 spec, i e 66 oil block and bigger hole drilled in crankcase to oil pump, drilled return oil pipe at tank bigger to match and Commando rocker pipe. With the benefit of hindsight, i wish i had left the 3 start gear alone. Why? It wet dumped more readily, the magneto oil seal kept needing replacing due to higher oil in crankcases. This drove me up the wall, as I had to make 100% sure that on replacement it fired at 0 & 180 degrees.
P.S. sorry I didn't see your earlier post on finding the cause.

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?

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600 had longer stroke , I think. It also had a different barrel to the 500. It is not unusual for a 500 to be bored + .060, my 500 is, but fitted with 10.0 or 10: 5 pistons from somewhere, probably a 650, with shirt shortenen to suit. If you can, I would avoid skimming head, once you have removed metal, you can't put it back.

The High comp pistons for the 600 bore were possibly Nomad Items. In !966 AMC were selling 500SS Nortons and up to then were likely to have been buying rods back from the dealers stocks , thought it may need some for future production or just spares for the thousands of 88/99 bikes still in use. A compression higher than 9 to 1 would be folly on these old clunkers.

norton bob said:

The High comp pistons for the 600 bore were possibly Nomad Items. In !966 AMC were selling 500SS Nortons and up to then were likely to have been buying rods back from the dealers stocks , thought it may need some for future production or just spares for the thousands of 88/99 bikes still in use. A compression higher than 9 to 1 would be folly on these old clunkers.

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Maybe, but my engine has a one piece Lansdown crank.

Norton cranks were pretty good in the road bikes, appart from an internal stress raiser . What rods are you using with that crank?.

No idea, for all i know they might be original.

My Atlas had the OPRV stick and it caused high pressure in the timing cover. It even INVERTED the crank oil seal in the timing cover. You might check that.

Some updates and pictures. Crank is now re-assembled and we're busy reassembling the motor. We also found loose valve guides in the head so decided to give the head a bit of a refurb too while we were at it.

So I haven't posted for a while - figured it's time for some feedback. Motor went back together really well and we took the time to go through everything thoroughly - we found a few other small issues - but all in all I'm very happy with the outcome - motor has really nice compression, doesn't smoke an is nice and quiet. I haven't managed to ride it much, because we encountered another problem which caused the rear wheel to lock up and actually break off the thread on the speedo drive! The previous owner obviously did not have a complete set of spacers for the rear wheel - more specifically the stepped one inside the hub so he made replacements out of Stainless Steel. He must have got the clearances slightly out because the axle friction welded itself to the SS spacers and destroyed the rear hub!

Luckily we found a complete replacement wheel from on of the Norton guys here, and we just rebuilt the wheel. Not a disaster, but took time!

I do have one question though and this is regarding the oil-line to the rocker cover.

The oil line from the top of the rocker cover comes down to a T-Piece in the return line from the oil pump which then exits at the top of the oil tank. When the bike is running, you can see oil returning to the oil tank, so I'm happy that the oil is circulating through the engine. How does oil get to the rockers though - does it go through internal passages and then drain via the oil line from the rocker cover, or is it supplied from the t-piece in the return line (which goes against my logic as the other end of the pipe to the oil tank is open so there is no pressure build-up)? On all the other bikes I have worked on, the feed to the rockers is on the positive side of the oil pump - but it has previously been confirmed on this site, all the oil line connections on my bike are correct.

I also see the oil line from the rocker cover is about half the diameter of the return line from the oil pump - which could in theory result in a venturi effect and allow oil to be sucked out the top of the head (assuming there are no leaks anywhere)- but with this bike and all it's non-standard bits those diameters might also be wrong. I just don't want to encounter any more lubrication issues, so thought it best to ask the experts before I ride the bike again.