Valves and valve seats

Your valves and seats will be fine, they are hardened already ex works so as long as they are within spec do not touch. If any specialist suggests other wise walk away and save the money.

John is quite correct about the seats being ok. Its the valves and guides that can be the problem when washed with unleaded and Ethanol rich fuel.

I had both a 650 and 750 cylinder head converted for unleaded fuel by different well-known Norton specialists. Both heads quickly started to show signs of losing compressionand within 5000 miles the valves needed recutting. There were serious craters in the new valve seats where the valves had been welding themselves to the seats. Both the valves and guides were changes on the 650 head and this cured the problem. I was informed that my Commando head was being damaged by too lean a fuel mixture. Really !!!! So how much damage do these Mikuni conversions cause?

Mike Pemberton had written about these issues in Roadholder and there are other good articles and comments within these Web pages.

I am with John and Phil on this one. If the valves, guides and seats are OK just leave them alone. Regarding balancing the crank, you won't know if it would benefit until you have the bike up and running. Crank balance is an interesting topic. What can suit one engine in a bike may not suit another. It is quite possible to have the crank balanced and end up with more intrusive vibration than you started out with.

Crankshaft balancing is one of those dark sciences that only the best specialists appear to have accurate knowledge about. For a lot of total engine rebuilds, it is a must due to the rubbish NOC members are being flogged as replacement pistons. Many versions being up to 50% heavier than standard originals.

The cheaper balancing act is the basic static process, where conrods and pistons are weighed and then, after a little Mathematics, holes are drilled into the crankshaft. It helps here if both pistons are near identical in weight .....the same for the conrods.

The more expensive balancing trick is the dynamic method where the crankshaft is spun; usually with weights bolted to the big end pins to duplicate the piston and conrod weights. Then some gadget calculates the position of where weight has to be added or subtracted to the crankshaft. Some specialists fill the crankshaft with oil to simulate the reality of when the engine is running.

For either method of balancing, someone has to be aware of the balance factor for the engine that the crankshaft is going into. This is so important. For example........ the 750 Commando crankshaft has a completely different balance factor to that of a 750 Atlas engine. I once had an Atlas crankshaft dynamically balanced and it transformed the whole motor into a turbine smooth performer capable of regularly punching up to 7000rpm. Completely rubbishing the previous myth of a 'jack hammer' performer.

Previously Phil Hannam wrote:

Crankshaft balancing is one of those dark sciences that only the best specialists appear to have accurate knowledge about. For a lot of total engine rebuilds, it is a must due to the rubbish NOC members are being flogged as replacement pistons. Many versions being up to 50% heavier than standard originals.

The cheaper balancing act is the basic static process, where conrods and pistons are weighed and then, after a little Mathematics, holes are drilled into the crankshaft. It helps here if both pistons are near identical in weight .....the same for the conrods.

The more expensive balancing trick is the dynamic method where the crankshaft is spun; usually with weights bolted to the big end pins to duplicate the piston and conrod weights. Then some gadget calculates the position of where weight has to be added or subtracted to the crankshaft. Some specialists fill the crankshaft with oil to simulate the reality of when the engine is running.

For either method of balancing, someone has to be aware of the balance factor for the engine that the crankshaft is going into. This is so important. For example........ the 750 Commando crankshaft has a completely different balance factor to that of a 750 Atlas engine. I once had an Atlas crankshaft dynamically balanced and it transformed the whole motor into a turbine smooth performer capable of regularly punching up to 7000rpm. Completely rubbishing the previous myth of a 'jack hammer' performer.

Hi Guys,

My 1968 Mercury has a serious vibration problem, wonder whether pistons fitted after a re-sleeve are the problem? Anyone know the weight of the original pistons?

Regards,

Chas

Previously chas_goupillot wrote:

Previously Phil Hannam wrote:

Crankshaft balancing is one of those dark sciences that only the best specialists appear to have accurate knowledge about. For a lot of total engine rebuilds, it is a must due to the rubbish NOC members are being flogged as replacement pistons. Many versions being up to 50% heavier than standard originals.

The cheaper balancing act is the basic static process, where conrods and pistons are weighed and then, after a little Mathematics, holes are drilled into the crankshaft. It helps here if both pistons are near identical in weight .....the same for the conrods.

The more expensive balancing trick is the dynamic method where the crankshaft is spun; usually with weights bolted to the big end pins to duplicate the piston and conrod weights. Then some gadget calculates the position of where weight has to be added or subtracted to the crankshaft. Some specialists fill the crankshaft with oil to simulate the reality of when the engine is running.

For either method of balancing, someone has to be aware of the balance factor for the engine that the crankshaft is going into. This is so important. For example........ the 750 Commando crankshaft has a completely different balance factor to that of a 750 Atlas engine. I once had an Atlas crankshaft dynamically balanced and it transformed the whole motor into a turbine smooth performer capable of regularly punching up to 7000rpm. Completely rubbishing the previous myth of a 'jack hammer' performer.

Hi Guys,

My 1968 Mercury has a serious vibration problem, wonder whether pistons fitted after a re-sleeve are the problem? Anyone know the weight of the original pistons?

Regards,

Chas

Hi Chas,

I have just rebuilt my 650SS and weighed the new pistons to compare against the originals. All up ( with rings and gudgeon) each new piston weighed 319g each against 325g for the used pistons. Both are standard bore.

regards, Ian

Check that your head steady bolts are fully tight. If they loosen, the vibration can be horrific - bad enough to shake the plates off the battery as I once found out.

Previously Phil Hannam wrote:

Crankshaft balancing is one of those dark sciences that only the best specialists appear to have accurate knowledge about. For a lot of total engine rebuilds, it is a must due to the rubbish NOC members are being flogged as replacement pistons. Many versions being up to 50% heavier than standard originals.

The cheaper balancing act is the basic static process, where conrods and pistons are weighed and then, after a little Mathematics, holes are drilled into the crankshaft. It helps here if both pistons are near identical in weight .....the same for the conrods.

The more expensive balancing trick is the dynamic method where the crankshaft is spun; usually with weights bolted to the big end pins to duplicate the piston and conrod weights. Then some gadget calculates the position of where weight has to be added or subtracted to the crankshaft. Some specialists fill the crankshaft with oil to simulate the reality of when the engine is running.

For either method of balancing, someone has to be aware of the balance factor for the engine that the crankshaft is going into. This is so important. For example........ the 750 Commando crankshaft has a completely different balance factor to that of a 750 Atlas engine. I once had an Atlas crankshaft dynamically balanced and it transformed the whole motor into a turbine smooth performer capable of regularly punching up to 7000rpm. Completely rubbishing the previous myth of a 'jack hammer' performer.

Hi Guys,

My 1968 Mercury has a serious vibration problem, wonder whether pistons fitted after a re-sleeve are the problem? Anyone know the weight of the original pistons?

Regards,

Chas

Now as for the 650 Mercury balance factor is 85% pistons were AE auto parts number 25387 lh and 25388 rh and its adviseable not to over bore a 650 so plus 40 is the maximum size you can go too , as for virbation your getting I found that looking at the engine plates is advisable as they do ware ovel and the stud may not be a snug fit for new nuts bolts and studs of all sizes try www. NooksNuts.co.uk these come in nickel and there very good , I have fitted On my Norton Manxman 650 one of the first 650s yours AJD

Hi all,

In the rebuild of twin engine I am not sure of what I should do as regards valves & valve seats, as they are original I guess that perhaps I would need to change for harder steel ? due to fuel, could someone please advise, thanks.

And also would it be adviseable to balance crankshaft, if so I dont know where to begin, could someone enlighten me please, thanks

If both these jobs are required is it essential that I use particular services?

Many thanks Jim

Now jim this is all down to the condion of the valves and seats them selfs

I have rebuilt many Norton cylinder heads , and Recut seat fitted new oversize

Valve guides I use Bronze valve guides as the ten time better than any cast iron valves guides you can get , When fitting new Guides you need to re-cut the seats too and lap in and do a gas test , for leaks from the valves , too do this is stright forward , you need to mix some engineers blue in with white spirt , fit the valve in with no spings head turned up ward on a bench or vice, fit two spark plugs , poor in the sprit mix and see if you have any leaks you need to leave it for ten minuits , if you cannot see and blue running out you got a good gas seal , if thre is blue running out you need some more lapping in, this may have be repeated , and check valve stem ware too with a digial micrometer for top to bottom and tuning the valve stem too take measurements at all intervels and write them down, the valve stem should read .309 to .310 wear no more than 1 thou. yours AJD

I agree with Anna that bronze is superior to iron for guides. If you use Colsibro bronze it will tolerate negligible lubrication and very tight tolerances without difficulty. There may be a ready-made guide in your local car-parts shop which could be adapted, otherwise you will need to buy it in bar and turn them up.

I agree with Anna that bronze is superior to iron for guides. If you use Colsibro bronze it will tolerate negligible lubrication and very tight tolerances without difficulty. There may be a ready-made guide in your local car-parts shop which could be adapted, otherwise you will need to buy it in bar and turn them up.

Hi Anna, I've bought assorted nuts & bolts from Nookie's Nuts in th epastbut I have only ever seen zinc-plated ones. Have you bought nickel-plated from him? I might go to Kempton Park next week where he often goes and check it out. (My luck that he won't be there!) Cheers, Lionel

Previously anna jeannette Dixon wrote:

Previously chas_goupillot wrote:

Previously Phil Hannam wrote:

Crankshaft balancing is one of those dark sciences that only the best specialists appear to have accurate knowledge about. For a lot of total engine rebuilds, it is a must due to the rubbish NOC members are being flogged as replacement pistons. Many versions being up to 50% heavier than standard originals.

The cheaper balancing act is the basic static process, where conrods and pistons are weighed and then, after a little Mathematics, holes are drilled into the crankshaft. It helps here if both pistons are near identical in weight .....the same for the conrods.

The more expensive balancing trick is the dynamic method where the crankshaft is spun; usually with weights bolted to the big end pins to duplicate the piston and conrod weights. Then some gadget calculates the position of where weight has to be added or subtracted to the crankshaft. Some specialists fill the crankshaft with oil to simulate the reality of when the engine is running.

For either method of balancing, someone has to be aware of the balance factor for the engine that the crankshaft is going into. This is so important. For example........ the 750 Commando crankshaft has a completely different balance factor to that of a 750 Atlas engine. I once had an Atlas crankshaft dynamically balanced and it transformed the whole motor into a turbine smooth performer capable of regularly punching up to 7000rpm. Completely rubbishing the previous myth of a 'jack hammer' performer.

Hi Guys,

My 1968 Mercury has a serious vibration problem, wonder whether pistons fitted after a re-sleeve are the problem? Anyone know the weight of the original pistons?

Regards,

Chas

Now as for the 650 Mercury balance factor is 85% pistons were AE auto parts number 25387 lh and 25388 rh and its adviseable not to over bore a 650 so plus 40 is the maximum size you can go too , as for virbation your getting I found that looking at the engine plates is advisable as they do ware ovel and the stud may not be a snug fit for new nuts bolts and studs of all sizes try www. NooksNuts.co.uk these come in nickel and there very good , I have fitted On my Norton Manxman 650 one of the first 650s yours AJD

Following Anna's advice about checking the seal between the valves and seats - you could always use vegetable colouring if you haven't got any engineer's blue. Red would be good as it looks like blood so you won't notice the cuts!

Following Anna's advice about checking the seal between the valves and seats - you could always use vegetable colouring if you haven't got any engineer's blue. Red would be good as it looks like blood so you won't notice the cuts!

Well Lionel if you need any engineering Blue I have a big tin full, it will be still there when I long gone, to the road in the sky, yours Anna J