New AN barrel & Emglo Pistons

Deets55 said:

...what is wrong with fitting the next size ring set and file fitting them to specs?

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"Danger Will Robinson!"

That's a good way to have snapped rings.

you can do this with compression rings as some suppliers will offer + 005 rings for this purpose but i would not do this with anymore than +010 ring and for sure not with a +020 ring set

Deets55 said:

what is wrong with fitting the next size ring set and file fitting them to specs? I would guess that the smaller expander ring should be used. I have seen this mentioned here before.
Pete

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SteveBorland said:

The issue here is the lower radial pressure rather than the gap. I think it was AE who did some testing and found that even with huge gaps (1/4" if I recall) there was virtually no extra leakage. However, if the bore is too large (or the ring too small), then the radial pressure drops off, resulting in decreased sealing. What Jim is suggesting (I think) is that the OP needs to find rings that will work in his slightly oversized bores.

/Steve in Denmark.

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I'm no expert or engineer, but we are talking about a thou and a half extra diameter (if the discrepancy is caused by big bores). That's not very much.

This issue has consumed me for the last 30 hours. I have decided to purchase +.020 pistons (from the same manufacturer) and get the clearance I want; I am mentally prepared to disassemble the lower end, if necessary, and start from scratch. I sell the motorcycles I build and want the next owner to have as much reliability as I can build in.

Thanks for all the great thinking y'all have put in the replies; a great wealth of knowledge!

Bill.

AN barrel is bored and honed to suit GPM pistons.

RoadScholar said:

This issue has consumed me for the last 30 hours. I have decided to purchase +.020 pistons (from the same manufacturer) and get the clearance I want; I am mentally prepared to disassemble the lower end, if necessary, and start from scratch. I sell the motorcycles I build and want the next owner to have as much reliability as I can build in.

Thanks for all the great thinking y'all have put in the replies; a great wealth of knowledge!

Bill.

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Bill, out of curiosity, why did you not buy barrels and pistons as a matched set from the same source?

Fast Eddie said:

RoadScholar said:

This issue has consumed me for the last 30 hours. I have decided to purchase +.020 pistons (from the same manufacturer) and get the clearance I want; I am mentally prepared to disassemble the lower end, if necessary, and start from scratch. I sell the motorcycles I build and want the next owner to have as much reliability as I can build in.

Thanks for all the great thinking y'all have put in the replies; a great wealth of knowledge!

Bill.

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Bill, out of curiosity, why did you not buy barrels and pistons as a matched set from the same source?

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i was wondering that,i have never actually bought new barrels but when i have had re bores done i always supply the pistons to the machine shop and then you can have what clearance you like,hope you get it sorted out

My machinist in Toronto said give me the new pistons so I can measure each one individually and bore to match. He used 2 drops of machinist's dye on the top of left and dyed the left barrel top. Then one drop for right side piston and barrel top. For no accidental switchings on the assembly. Many miles on these now with no oil consumption.

Triton Thrasher said:

comnoz said:

Believe me, you will never know the difference between .0045 and .006 in operation with full skirt pistons. Jim

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That's too obvious and easy.

Knurl! Blast! Bore! Balance!

And above all- worry!

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Well, you clearly blew past the Cryo treatment.

Brooking 850 said:

Dances, yes a slight peening up inside the skirts close to the gudgeon area will do the trick, there is a machine that can do that, my engine guru guy here has one.
Regards mike

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Well, I was just trying to be humorous and I now see where that gets me.

I did a google search on Kotherise, Kotherised and Kotherising and did not come up with anything relevant which is unusual. Is this a regional description for a process?

Madnorton said:

AN barrel is bored and honed to suit GPM pistons.

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I certainly hope it is the other way around. I would be screaming pissed if the barrels were anything other than original grade A 2.8746/2.8750" or grade B 2.8750/2.8754, does Joe make a combined sloppy grade AB 2.8746/2.8754"? All my new pistons are pretty much 2.8700/2.8705"
IF the barrels are to those spec's, I'd still buy and use them.
4.1-5.4 thou clearance
If I was building a hot engine I might hone a little bit if clearance on the low side. All assuming 12% AL lowex pistons of course. Does anyone offer 18 or 24% AL super low ex for nortons? I don't do much shopping for parts any more.

I don't worry too much about bore clearance - but probably I should. I use methanol fuel which makes the engine run much cooler, so I always warm the engine up very well prior to riding the bike.

Fast Eddie said:

RoadScholar said:

This issue has consumed me for the last 30 hours. I have decided to purchase +.020 pistons (from the same manufacturer) and get the clearance I want; I am mentally prepared to disassemble the lower end, if necessary, and start from scratch. I sell the motorcycles I build and want the next owner to have as much reliability as I can build in.

Thanks for all the great thinking y'all have put in the replies; a great wealth of knowledge!

Bill.

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Bill, out of curiosity, why did you not buy barrels and pistons as a matched set from the same source?

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This morning I would have been embarrassed to admit that I didn't have a good answer to that question.

I took the barrel and pistons for a second opinion on the slim possibility of "growing" the pistons to fit before committing to an overbore, or connecting with AN about a set of their pistons (the awakening), I have used this service for years. Using his measuring equipment he showed me that the bores were tapered, an aspect that I missed, showing about .006 skirt clearance at the top and about .010 at the bottom; no piston would be happy in these holes. So I went looking for Emglo +.020s; I ended up with .040s, no one I contacted had +.020s.

If anyone has a set of 750 Emglo +.020s I'm very interested, assuming they come with pins, clips and Hastings (or equivalent) rings; they are more likely to be closer in weight to the standard pistons that the engine was balanced with.

It never occurred to me to doubt the fitment of the new barrel, I am still quite happy to have it, and will purchase many more. I could have saved myself a lot of time and aggravation, if I had just measured it when it arrived then I could have purchased any quality oversize piston set, had the bores cut and got everything balanced in a smooth process. I'm not sure what I was thinking at the time, I should know better; very few Norton parts fit correctly out of the box.

Again, many thanks for the global inputs.

I think you are being very generous/gracious to AN by considering to sort this issue yourself.

Granted, original NOS could be a bit of hit & miss regarding manufacturing tolerances (bit of a generalisation but I always think that Brit bike bits need to be 'fitted' and not just 'installed') but I would expect, not unreasonably, that new barrels should be produced to modern standards with correct tolerances for at least the std pistons AN sell.

For you as the customer to go through the expense of having to source oversize pistons & bore out the new std barrels, IMHO, is unacceptable.

Why not get in touch with AN, explain your engineers report and see if you can come to some arrangement with AN about getting a set of matched std barrels & pistons that they can guarantee have the correct tolerances? I'm sure AN would be keen on dealing with you to get this sorted.

If anyone has a set of 750 Emglo +.020s I'm very interested, assuming they come with pins, clips and Hastings (or equivalent) rings; they are more likely to be closer in weight to the standard pistons that the engine was balanced with.

I did a search on eBay for: norton commando 750 piston set .020

There are at least 5 sets on eBAy now which all appear to be EMGO with Hastings rings; here's one of them:
http://www.ebay.com/itm/Norton-750-Comm ... hb&vxp=mtr
This guy is in MIchigan

Here's another set closer to you (Acushnet, MA): http://www.ebay.com/itm/Norton-Atlas-75 ... BA&vxp=mtr

click said:

I think you are being very generous/gracious to AN by considering to sort this issue yourself.

Granted, original NOS could be a bit of hit & miss regarding manufacturing tolerances (bit of a generalisation but I always think that Brit bike bits need to be 'fitted' and not just 'installed') but I would expect, not unreasonably, that new barrels should be produced to modern standards with correct tolerances for at least the std pistons AN sell.

For you as the customer to go through the expense of having to source oversize pistons & bore out the new std barrels, IMHO, is unacceptable.

Why not get in touch with AN, explain your engineers report and see if you can come to some arrangement with AN about getting a set of matched std barrels & pistons that they can guarantee have the correct tolerances? I'm sure AN would be keen on dealing with you to get this sorted.

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Indeed.

I agree that if you bought the barrels as new manufacture then there is no excusing the fact that they are out of tolerance.
The thought of having them machined to + 40's seem ludicrous as that immediately reduces the life span of a very costly part.
Im sure that AN will redress the issue and cannot understand why you would accept them.

Sorry, just my thoughts!

Something not right here, AN barrels are bored to suit GPM pistons which have a smaller clearance than the original pistons. If I remember correctly the bore is less than 73mm - if they had been bored to the original size then your pistons would have even more clearance. Anyone currently trying to fit a set of standard pistons to an original std bore will have more gap - fact, piston to bore clearances are narrowing, the latest I have just seen is 0.003''
I also have a set of Hastings 750 plus 20 rings, these were going to be fitted to a original JC pistons from the 70's - I decided not too as the oil scraper riais seem to be a compromise to fit both narrow and wide oil control ring gaps.

Dances with Shrapnel said:

Triton Thrasher said:

comnoz said:

Believe me, you will never know the difference between .0045 and .006 in operation with full skirt pistons. Jim

Click to expand...

That's too obvious and easy.

Knurl! Blast! Bore! Balance!

And above all- worry!

Click to expand...

Well, you clearly blew past the Cryo treatment.

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Yes- and freeze its ass!

Searches for pistons will go better if you don't put an extra L in Emgo.

I believe Emgo are rebranded Taiwanese JCC pistons. So are Hepolite and Harris, though I don't know if Harris does Norton ones.