1969 750 Engine Rebuild being Rebuilt

Pdr206 · Nov 28, 2022

Had the engine rebuilt by a shop. $x,xxx amount later, I'm having to buy the correct and sometimes unbroken parts in order to build it myself. These are some questions that I have seen several answers to, so am coming to the well.

Currently the cylinder jug is bored 040 over with hepolite pistons. There appears to be 4 thou clearance (on one side of piston to wall). What SHOULD the piston to wall clearance be?
Currently the oil rings have 0" end gap. What should it be? Have seen several magic numbers.
Where can I get correct diameter whitworth helicoils for the cylinder jug? (currently there are 3 SAE helicoils and the threads are pulling out of a few other threaded holes.)
Each one of my pushrods looks different, and the tappets would not budge until cylinder/head were dissasembled. What/how do I figure out correct pushrod length?

What else should I be on the lookout for while this engine is apart? We already found there was no timing parts and the gearbox was rebuilt incorrectly. Is it worth taking the rockers apart?

Shop was 'returned' to original owner by the time all this was known. Just trying to do it right but obviously have some tolerance questions.

Thank you in advance.

concours · Nov 28, 2022

You should have the shop manual before you touch another wrench. Free downloads are available.

Question EVERYTHING.

Search function is your friend.

Pdr206 · Nov 28, 2022

Have the shop manual and several other rebuild books. Am just a bit sketched out after what happened to me.

L.A.B. · Nov 28, 2022

concours said:
You should have the shop manual before you touch another wrench.

However, the information requested (oil control ring gap and skirt clearance) isn't in either the '68 - '70 or later ('71 - '74) manuals.

Pdr206 said:
Currently the cylinder jug is bored 040 over with hepolite pistons. There appears to be 4 thou clearance (on one side of piston to wall). What SHOULD the piston to wall clearance be?

Presumably, these are JCC Hepolite and not original Hepolite?

JCC Std Piston Size for 750

As part of my rebuild, I'm replacing my original 1971 pistons with the slot behind the oil ring. I had a local machinist check my cylinder bores and they measure 2.8750 (the bike only has 13,000 miles). I asked a guy in a parts shop over the phone to measure the standard sized JCC pistons he had...

www.accessnorton.com

Pdr206 said:
Where can I get correct diameter whitworth helicoils for the cylinder jug?

Whether 3/8" x 26 for the head bolt holes or 5/16" x 26 for the front stud holes then the only commonly available Helicoil kits are 3/8" x 26 and 5/16" x 26 BSC (British Standard Cycle thread, not Whitworth).

British Threads - British Standard Cycle

britishfasteners.com

Not all British threads are Whitworth.

baldy · Nov 28, 2022

Look in the shop manual technical data section.
Top ring gap .010-.012
middle ring .008- .012
lower oil scraper rings are not gapped
You have to do some math for the piston to bore gap based on standard.

ashman · Nov 28, 2022

Another story of bad workmanship from a shop and at a big cost to the owner to find things later that wasn't done right at all, I am self-learned from working on my Norton for 46 years and have done a few rebuilds over that time on my own Norton as well others, a few friends over the years has seen how good my bike has been to put their trust in me to do their rebuilds mostly I pull them apart tell them what is needed in parts and what parts need to be sent away for machine work once all done to reassemble their motors or GB, I no longer do this as so many time is wasted for things to get done and getting paid for my work and time.
Once I did a motor/GB rebuild for a friend who paid good money for his Norton, he paid me for all the parts needed and I trusted him to give his motor back to finish off the bike before paying me for my work time, he then found out the bike was stolen so I never did get paid for my time and effort although had no idea the bike was stolen, I put a lot of time on the motor and GB, then he had the hide to ask me to pull the motor down to replace the crank case that weren't stolen, I told him straight away I don't want nothing to do with that, I am a honest person and now knowing its stolen I don't want no part of it, already been burnt for what I did on it, so now I no longer do work on others unless paid up front beforehand, last 2 jobs I got burnt by trusted friends so no more I do my own work.
Shame really as the rebuilds I have done are all still going good as I take pride in my work, but help friends out to just get burnt is not worth my time no longer.
There is one engine rebuilder for all British bikes not far from me and a lot of my mates have sent work to him to be done to have spent a lot of money to have things not right, rebores that has too much clearance between bore and final hone is one problem or motors ceasing up before they have even run in, I kept telling them that this so call engine builder is no good but do they listen, no and still give him work even when they been burnt, why have a British bike if they not willing to learn or ask for help as I am always willing to help no matter what.
Anyway hope things work out for the OP and if he gets into trouble there is aways someone here to help out, it's what good forum are all about.

Ashley

concours · Nov 28, 2022

baldy said:
Look in the shop manual technical data section.
Top ring gap .010-.012
middle ring .008- .012
lower oil scraper rings are not gapped
You have to do some math for the piston to bore gap based on standard.

That's where I got the piston clearance, a small bit of arithmatic, from the dimensions published in the shop manual.

The oil ring is "always more" than the published compression rings.

Torontonian · Nov 28, 2022

ashman said:
Another story of bad workmanship from a shop and at a big cost to the owner to find things later that wasn't done right at all, I am self-learned from working on my Norton for 46 years and have done a few rebuilds over that time on my own Norton as well others, a few friends over the years has seen how good my bike has been to put their trust in me to do their rebuilds mostly I pull them apart tell them what is needed in parts and what parts need to be sent away for machine work once all done to reassemble their motors or GB, I no longer do this as so many time is wasted for things to get done and getting paid for my work and time.
Once I did a motor/GB rebuild for a friend who paid good money for his Norton, he paid me for all the parts needed and I trusted him to give his motor back to finish off the bike before paying me for my work time, he then found out the bike was stolen so I never did get paid for my time and effort although had no idea the bike was stolen, I put a lot of time on the motor and GB, then he had the hide to ask me to pull the motor down to replace the crank case that weren't stolen, I told him straight away I don't want nothing to do with that, I am a honest person and now knowing its stolen I don't want no part of it, already been burnt for what I did on it, so now I no longer do work on others unless paid up front beforehand, last 2 jobs I got burnt by trusted friends so no more I do my own work.
Shame really as the rebuilds I have done are all still going good as I take pride in my work, but help friends out to just get burnt is not worth my time no longer.
There is one engine rebuilder for all British bikes not far from me and a lot of my mates have sent work to him to be done to have spent a lot of money to have things not right, rebores that has too much clearance between bore and final hone is one problem or motors ceasing up before they have even run in, I kept telling them that this so call engine builder is no good but do they listen, no and still give him work even when they been burnt, why have a British bike if they not willing to learn or ask for help as I am always willing to help no matter what.
Anyway hope things work out for the OP and if he gets into trouble there is aways someone here to help out, it's what good forum are all about.

Ashley

How true. I've learnt to not lend tools anymore.
A fool and his tools are easily parted.
Never seen money from any of my bikey friends here , for me to race over and fix things. Just beers and vino or smoke. Thank you's too.
If it's big I tell them to order in the list of parts and call me when they arrive. More booze , food , smoke . Once cocaine and babes but only because of the big X-mas bonus night. Fun.
Or refer them to a good local machine shop familiar with British motorbikes ( Gord Bush Performance ).
Never bumped into stolen .

Pdr206 · Nov 29, 2022

Thank you all. Had seen the information in the technical data section but wanted to make sure of accuracy of data. Simple confirmation of data, thats all. Too many forum posts with differing opinions of what numbers to use.

LAB-thank you as always for the straightforward non-snarky response. If I wanted attitude I'd go talk to my wife.

Have the Workshop Manual, Norman Whites manual, Norton Int'l Owners Association Tech Digests and a near useless 'How to Restore a Norton Commando' book.

TomU · Nov 29, 2022

I found Mick Hemmings videos one of the best DIY resource out there. You can get them through INOA

1969 750 Engine Rebuild being Rebuilt

Pdr206

concours

Pdr206

L.A.B.

Moderator

JCC Std Piston Size for 750

British Threads - British Standard Cycle

baldy

ashman

concours

Torontonian

Pdr206

TomU

1972 Roadster

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