‘71 Norton Cylinder ID

[Crankhead]

Hi everyone new in forum but I’ve been reading lots of great thread here quite sometimes now,I have a question regarding my recent basket case 71’ norton 750 regarding cylinder head and cylinder barrel, on the plastic bin where the both cylinder head are there is a piece on stick on paper says dunstall top end, but where measure the cylinder barrels they are measuring like a standard size and also the intake valve they like standard size also, but both cylinder head and barrel they kinda rough in finish.

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[L.A.B.]

Welcome,

Unfortunately, the pictures in your Photobucket link aren't public so require a sign-in.
A long story but many of us don't use Photobucket anymore so might not have a P/bucket account there now.

This thread has been moved to the Classic Commando section for the time being unless it develops into a rebuild/restoration thread.

 

[marshg246]

Hi everyone new in forum but I’ve been reading lots of great thread here quite sometimes now,I have a question regarding my recent basket case 71’ norton 750 regarding cylinder head and cylinder barrel, on the plastic bin where the both cylinder head are there is a piece on stick on paper says dunstall top end, but where measure the cylinder barrels they are measuring like a standard size and also the intake valve they like standard size also, but both cylinder head and barrel they kinda rough in finish.

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A private space for your group's photos and videos. Share, react, and relive moments together. Available on iOS, Android, and desktop. Free for new sign-ups.

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Especially starting out a VIP membership would help you mostly because you can post pictures directly and you get no ads.

Look carefully at all numbers and other marks on both - may help. I know nothing about Dunstall parts (many here do) but I know most of the marks on Norton cylinders, crankcases, and heads when I see them.

 

[lcrken]

Well, one of the obvious differences in the cylinders is that the Dunstalls are aluminum and the stock are cast iron. That should be pretty easy to check . The heads sound like standard Commando heads. Dunstall didn't make heads, they just did big valve and porting conversions on stock heads.

If you change your Photobucket pictures to public, and provide a link to those photos, at least some of us can see them.

Ken

 

[APRRSV]

Hi everyone new in forum but I’ve been reading lots of great thread here quite sometimes now,I have a question regarding my recent basket case 71’ norton 750 regarding cylinder head and cylinder barrel, on the plastic bin where the both cylinder head are there is a piece on stick on paper says dunstall top end, but where measure the cylinder barrels they are measuring like a standard size and also the intake valve they like standard size also, but both cylinder head and barrel they kinda rough in finish.

Private Group Photo & Video Sharing

A private space for your group's photos and videos. Share, react, and relive moments together. Available on iOS, Android, and desktop. Free for new sign-ups.

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Dunstall sold many 750 (iron barrel) Commando's with the Dunstall modified cylinder head. He sold one to me more than 50 years ago.
The Dunstall modified cylinder head had larger intake valves with an altered valve angle. This resulted in requiring larger diameter valve guides. A photo of the intake valve guide may help identify.

Ed

 

[lcrken]

Dunstall sold many 750 (iron barrel) Commando's with the Dunstall modified cylinder head. He sold one to me more than 50 years ago.
The Dunstall modified cylinder head had larger intake valves with an altered valve angle. This resulted in requiring larger diameter valve guides. A photo of the intake valve guide may help identify.

Ed

No doubt, but that doesn't make the cylinder a Dunstall, just a stock Commando iron cylinder. All the Dunstall made cylinders were aluminum, and a fairly soft grade of alloy at that. They were famous for having to regularly tighten the base nuts as they dug further into the cylinder flange.

@Crankhead: The difference between a Dunstall cylinder and a stock Commando cylinder is pretty obvious. These are two pictures of a Dunstall cylinder. If yours doesn't look pretty much like this, it's not a Dunstall.

But note that I have seen Dunstall cylinders without the Dunstall name. This is one where someone has deliberately ground off the name.

Ken

 

[APRRSV]

No doubt, but that doesn't make the cylinder a Dunstall, just a stock Commando iron cylinder. All the Dunstall made cylinders were aluminum, and a fairly soft grade of alloy at that. They were famous for having to regularly tighten the base nuts as they dug further into the cylinder flange.

@Crankhead: The difference between a Dunstall cylinder and a stock Commando cylinder is pretty obvious. These are two pictures of a Dunstall cylinder. If yours doesn't look pretty much like this, it's not a Dunstall.

View attachment 99142

View attachment 99143

But note that I have seen Dunstall cylinders without the Dunstall name. This is one where someone has deliberately ground off the name.

View attachment 99144

Ken

Hi Ken,
I didn't mean to imply that the iron cylinder was a Dunstall cylinder. My point was that the motor could well have been built by Dunstall, as mine was, if the cylinder head was a Dunstall modified head.

Ed

 

[KiwiShane]

No doubt, but that doesn't make the cylinder a Dunstall, just a stock Commando iron cylinder. All the Dunstall made cylinders were aluminum, and a fairly soft grade of alloy at that. They were famous for having to regularly tighten the base nuts as they dug further into the cylinder flange.

@Crankhead: The difference between a Dunstall cylinder and a stock Commando cylinder is pretty obvious. These are two pictures of a Dunstall cylinder. If yours doesn't look pretty much like this, it's not a Dunstall.

View attachment 99142

View attachment 99143

But note that I have seen Dunstall cylinders without the Dunstall name. This is one where someone has deliberately ground off the name.

View attachment 99144

Ken

I've got one with a slight crack through the D...

 

[Crankhead]

I appreciate all the replies, ok another question are valve collect,valve collar and valve spring seat suppose to be aluminums?thanks.

Hope my photo works now I upgrade my membership to VIP.

 

[baz]

I appreciate all the replies, ok another question are valve collect,valve collar and valve spring seat suppose to be aluminums?thanks.

Hope my photo works now I upgrade my membership to VIP.

No they are not aluminium/ duralumin as standard
Be careful if you use those ,I have known the valve collets do dig in making them very hard to remove

 

[lcrken]

As baz said, No. The stock valve retainers, collets, and spring seats are steel. There were a lot of aftermarket spring kits available back in the day that used aluminum seats and retainers, but I've never seen one with aluminum collets before. That sounds scary. I've used the aluminum retainers in the past with no problems, but there have been cases where the collets pulled through the aluminum retainers, with disastrous results. The better designed aluminum retainers used a wider angle collet to prevent pull through, but I would still be nervous about using them. The stock steel retainers work just fine in most cases. The current standard for high performance spring kits seems to be titanium retainers.

As best I recall, Dunstall did not sell any special retainers, collets, or spring seats. But you can never be sure what he might have done for any particular engine build. I have only seen one of his big valve heads up close, and it had stock Commando retainers, collets, and spring seats, but I don't know if that was original. He did recommend S&W valve springs, which he sold, but as bare springs, not with the other bits. There is a picture in his tuning book that shows a polished retainer with lightening cuts, but that was a common practice back then on stock retainers used in racing Nortons.

Have you looked at the lifters, to see if they have been lightened? That was another common Dunstall practice.

Ken

 

[Crankhead]

@Icrken how can I tell if my lifters been lightened?

Try to gather more info about all the parts I’ve got before I start my rebuilding project.

Like this camshaft that was wrapped with bubble plastic wrap with blue rug in it looks brand new,thanks.

 

[APRRSV]

@Icrken how can I tell if my lifters been lightened?

Try to gather more info about all the parts I’ve got before I start my rebuilding project.

Like this camshaft that was wrapped with bubble plastic wrap with blue rug in it looks brand new,thanks.

Hi Crankhead, If the lifters were lightened, as they were on my Dunstall Commando, you will see that the hollow space (looking from the side) has een lengthend vertically and widened horizontally and polished around the edges.

Ed