Dominator 88

Andymann said:
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.
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Oil is pumped from the engine to the tank through the return line therefore also flows to the rockers.

There is normally a restriction in the return line to the oil tank which forces a certain amount of oil in the direction of the rockers and that's normal for the majority of British bikes. British bikes with a high-pressure rocker feed (Norton twins from '66 for instance) are one exception.
 
Andymann said:
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.
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Basically the oil system was changed when Norton went over to a six speed oil pump worm creating double speed.
The oil union on the crankcase had bigger holes in the pipe with the crankcases oil holes to/ from the pump drilled bigger, also the Commando rocker oil feed was fitted.
I assume that the return oil pipe inside the oil tank might, I repeat, might have been made bigger, however, I can find no information on that.
I don't want to re read your posts but have you a 3 or 6 start worm on your oil pump?
 
I have a normal 3 start pump.

What I see now to be a problem is that this bike has a glass-fibre replica Manx tank and I bet the original owner hasn't fitted the restriction.

Thanks for the info - another thing I will need to check!
 
Andymann said:
I have a normal 3 start pump.

What I see now to be a problem is that this bike has a glass-fibre replica Manx tank and I bet the original owner hasn't fitted the restriction.

Thanks for the info - another thing I will need to check!
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Watch out if you are using fuel with ethanol it will destroy your glass tank.
 
N0rt0nelectr@ said:
Watch out if you are using fuel with ethanol it will destroy your glass tank.
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As he says the tank probably does not have a restriction then we are talking oil tank, hopefully. The restriction being needed to force some oil to go to the rockers as the rocker feed on 3 start pumps comes from the oil return.
 
hello now this engine number is from 1952 export bike and the oil pump was a 3 start so that leave me thoughts ether someone as blocked off a breather somewhere or the presser release is not working and two if someone as being trying to make a cafe racer they may have fitted parts that are not suitable to this engine early twins did not like being tampered too much these bike were not made for racing so If I were you I would pull the engine and do a strip down and assess all the engine components to the correct specification of that period
 
The std oil return assembly usually works ok as long as it occasionaly flushed through , Its not really up to it if the motor is used at low revs or for short journeys. The factory used to reccomend the use of a Jubilee 250cc model assembly to increase flow. It usually provides too much flow and a bigger bore (changed bias) works better .Can't remember what size I finished up with ,but if you put in a brass insert with a !/8" hole up to the tank and progressively drill out till the flow is what you want ,that will do it. Easy to do as no oil flows out of a Norton tank when the assembly is removed ,yours may be different if not a Norton made tank!!.
 
Bernhard said:
They stopped calling them Domi twins when they went to the 750 Atlas, more or less. (although some people will disagree with me- it's still the same engine)
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well it may look something like but in fact the dimensions of the bigger engines are not the same as the model 88 as these engine are that bit smaller
 
annajeannette said:
well it may look something like but in fact the dimensions of the bigger engines are not the same as the model 88 as these engine are that bit smaller
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4 different cases:
1 very early M7,
2 later M7/88/99 dynamo,
3 early alternator 88/99,
4 then last from the rear bulge cases starting with the 1960 650/88/99 atlas ( and a few earlier ones) the timing case CASTING # did not change until the single chain/20M3S commando starting in 1969 with the "S"
Strange? The castings are the same # arent they? So the only difference would be small barrel bolt pattern 500/600/650 or large barrel bolt pattern for 750's

Case the same size ....only the barrels are different
 
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I think you will not just find the cases are not the same , but also as the engines were bored/ stroked the holes on a 750 barrel will no way match a 500 and vice versa.
 
annajeannette said:
well it may look something like but in fact the dimensions of the bigger engines are not the same as the model 88 as these engine are that bit smaller
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I agree with your comment , but I think I have been quoted out of context.
I cannot find anywhere advertised published material that Norton ever described the 750 as a dominator. Can you?
 
Bernhard said:
I think you will not just find the cases are not the same , but also as the engines were bored/ stroked the holes on a 750 barrel will no way match a 500 and vice versa.
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I'm wondering about this.

If a 750 barrel and head will not bolt up to an earlier "Dominator" case, but you can build a 500 on any 600 or 650 case, the 88ss and 650ss cases are the same, including the crank clearance bulge, though unneeded on the 88ss. Short of that bulge, the "Dominator" cases are dimensionally the same, yes?

As for the Atlas, the timing sprockets and chains are all the same as the Domis, the crank cheeks are the same as the 650ss, as is the exhaust, and the heads are the same casting numbers, and they all bolt up to the same engine plates. Short of the stud spacing and diameters on barrels and heads, and bore for barrels, where do I look for dimensional differences? They all seem to occupy the same space, other than the 8 or 9 fin height.
 
WE agree...
When they went to the bulge cases the castings # are all the same, but not the norton part# the 122/16/18 engines are all machined up as small bolt pattern and use the same PN., Only the 62+ atlas was machined for the bigger bolt pattern of the bigger desaxe barrels and this may justify dropping the dominator name and a different PN....sorry not my fight LOL. However the domi name is used across different rolling chasssis, gardengate, wide line and slimline featherbed) AND across different engine sizes. To me it is a meaningless expression of endearment that sofar defies definition. LOL
 
Just learnt that the last 650 motors built used modified Commando cases , what did they do about barrels I wonder.
 
norton bob said:
Just learnt that the last 650 motors built used modified Commando cases , what did they do about barrels I wonder.
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What is to just learn? We've been saying it over and over the crankcase castings are the same for all 61+ late domi and commando through 20M3 which we now know as fastbacks as late as early 70 . just drill/tap the cases for small bolt pattern barrels makes them for 650 or 122(88)....The barrels HAD TO BE 650 as they were small head bolt pattern and atlas were desaxe medium head bolt pattern.

The 650 is not a desaxe engine...sleeve it and offset rebore......not likely. Possibly if it was bored small and correctly repositioned. Ever heard of a small bore large bolt pattern OEM barrel????
What am I missing? It's not complicated
Only thing that may have changes is the cam end breather changed to atlas style instead of rear case exit???? who knows . anyone seen a mercury?
Repositioning the case head drain down hole is a minor issue?
 
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dynodave said:
What is to just learn? We've been saying it over and over the crankcase castings are the same for all 61+ late domi and commando through 20M3 which we now know as fastbacks as late as early 70 . just drill/tap the cases for small bolt pattern barrels makes them for 650 or 122(88)....The barrels HAD TO BE 650 as they were small head bolt pattern and atlas were desaxe medium head bolt pattern.

The 650 is not a desaxe engine...sleeve it and offset rebore......not likely. Possibly if it was bored small and correctly repositioned. Ever heard of a small bore large bolt pattern OEM barrel????
What am I missing? It's not complicated
Only thing that may have changes is the cam end breather changed to atlas style instead of rear case exit???? who knows . anyone seen a mercury?
Repositioning the case head drain down hole is a minor issue?
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My Mercury motor has no cam end breather as an Atlas would.
 
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