71 norton top end break in now?

Re: Gathering top end tips!!! 71 norton....

Rohan said:

concours said:

You are correct... not a lot of difference. But, we ARE measuring TENTHS, and we ARE purposely machining a NEW rebuild OUT of tolerance. The "Lot better to have a shade loose than tight" is an old wives tale, retold by the unknowing. If a machinist can't hold the tolerance specified, you are IN THE WRONG SHOP. The thrust of this post is... wait for it... A COMMON MISCONCEPTION IS THAT A LOOSE PISTON IS LESS LIKELY TO SEIZE THAN A PROPER CLEARANCED ONE.

Click to expand...

Old british bike boards are full of stories of rebores where the cylinders were bored too tight = watercooled car clearances - and subsequently had a tight piston or 2. Someone here bought a cheap Trident - when it warmed up, the engine became tight. Car clearances on the pistons....

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LOL, Not looking for a pissing match, just talking ACTUAL ACCURATE MEASUREMENTS, rather than "stories".

Can you explain why IT-L's end gaps are .008" OUT OF TOLERANCE? Maybe the piston makers didn't read the "stories".

Re: Gathering top end tips!!! 71 norton....

concours said:

Can you explain why IT-L's end gaps are .008" OUT OF TOLERANCE? Maybe the piston makers didn't read the "stories".

Click to expand...

Obviously something is deeply wrong there, and needs to be put right.

P.S. I read that as one ring was that far out, not the whole set. ?

Wouldn't be the first time an oversize ring set had a smaller ring included in the 'set'.
Quality control is everything when dealing with such similar items.

Re: Gathering top end tips!!! 71 norton....

Rohan said:

iceteanolemon said:

What ring gaps are everyone running with the JCC rings and pistons? I just measured and one of the rings comes to 20 thou....

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concours said:

.010"

Click to expand...

The general rule is 4 thou endgap per inch of bore.

That makes about 12 thou for a 750 Commando.
JCC rings would want to be something special to go with less than that ??

Click to expand...

Spec is .010-.012 top ring, .008-.012 middle ring. If you put those rings in a proper size bore, my experience says the end gap will FALL RIGHT IN SPEC.

Re: Gathering top end tips!!! 71 norton....

Rohan said:

concours said:

Can you explain why IT-L's end gaps are .008" OUT OF TOLERANCE? Maybe the piston makers didn't read the "stories".

Click to expand...

Obviously something is deeply wrong there, and needs to be put right.

P.S. I read that as one ring was that far out, not the whole set. ?

Wouldn't be the first time an oversize ring set had a smaller ring included in the 'set'.
Quality control is everything when dealing with such similar items.

Click to expand...

You are correct. The bore is oversized, out of spec. A hole shrinker oughta do it... I read it as he only measured one ring. (so far) :?:

Re: Gathering top end tips!!! 71 norton....

concours said:

LOL, Not looking for a pissing match, just talking ACTUAL ACCURATE MEASUREMENTS, rather than "stories".
.

Click to expand...

Just looking to keeping a balanced view here.
Boring too tight can be quite destructive....

Surprised no-one has recommended breaking rings in dry.
Good and quick for race motors, but road bikes ??

Re: Gathering top end tips!!! 71 norton....

Rohan said:

concours said:

You are correct... not a lot of difference. But, we ARE measuring TENTHS, and we ARE purposely machining a NEW rebuild OUT of tolerance. The "Lot better to have a shade loose than tight" is an old wives tale, retold by the unknowing. If a machinist can't hold the tolerance specified, you are IN THE WRONG SHOP. The thrust of this post is... wait for it... A COMMON MISCONCEPTION IS THAT A LOOSE PISTON IS LESS LIKELY TO SEIZE THAN A PROPER CLEARANCED ONE.

Click to expand...

Measuring tenths ?? of what ??
The difference between 0.0047" and 5 thou is three tenths of a thou ?!!
The difference between a coarse crosshatch hone and a fine one is more than that...

Guzzi and BMW etc size their pistons in tenths of thous, never seen A,B,C on brit bike pistons ?? Hepolite piston sizes are quoted +/- 0.001 (1 thou)...

Click to expand...

Tenths of a thousandth of an inch. Standard machine shop vernacular. The factory workshop manual DOES mention "GRADE A and GRADE B" cylinder bores suggesting there was some sorting going on based on as built dimensions.

Re: Gathering top end tips!!! 71 norton....

Rohan said:

concours said:

LOL, Not looking for a pissing match, just talking ACTUAL ACCURATE MEASUREMENTS, rather than "stories".
.

Click to expand...

Just looking to keeping a balanced view here.
Boring too tight can be quite destructive....

Surprised no-one has recommend breaking rings in dry.
Good and quick for race motors, but road bikes ??

Click to expand...

Previously AGREED. The MINIMUM clearance will work fine. Less than is not recommended. I am not suggesting LESS than published minimum.

Re: Gathering top end tips!!! 71 norton....

concours said:

The factory workshop manual DOES mention "GRADE A and GRADE B" cylinder bores suggesting there was some sorting going on based on as built dimensions.

Click to expand...

I saw that - but the pistons are not graded into A and B, like Guzzi or BMW are ???

Re: Gathering top end tips!!! 71 norton....

Rohan said:

concours said:

Book says .0033" to .0047" clearance. I hate to be a buzz kill, but it's so predictable. Your piston ring end gaps will likely be out of spec as well, due to the bore size. :cry:

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Not a lot of difference between 5 thou and 0.0047" ?!!

When you see a worn engine, the clearances can get a LOT bigger than that. (and still run well !).
Lot better to have the pistons a shade loose than a shade tight too - a partial/seizure can spoil your day - big time.

Definitely check the ring end-gaps FIRST, by fitting loose into the bore.
Some rings can be too complete here - and need to be fitted for size.
No end gap can spoil your day too.

Click to expand...

Yup, they still run pretty good when all bagged out. My 850 had 80 PSI compression, started and ran great, no visible smoke. Felt a little pokey, but the timing was wicked retahded.. so hard to say what was worse. When I tore it down, the ring end gap was .028"..
My point is, going through all the time, effort, and $$$ to rebuild, why not get it right? Doesn't cost a cent more to do it RIGHT.

Re: Gathering top end tips!!! 71 norton....

Rohan said:

concours said:

The factory workshop manual DOES mention "GRADE A and GRADE B" cylinder bores suggesting there was some sorting going on based on as built dimensions.

Click to expand...

I saw that - but the pistons are not graded into A and B, like Guzzi or BMW are ???

Click to expand...

Not that I'm aware of. The Rotax engines I've rebuilt have size sorted (OEM pistons ONLY) piston options. Why do you suppose they go to all the trouble of size sorting? Because SIZE MATTERS! A few tenths MATTERS!

Re: Gathering top end tips!!! 71 norton....

concours said:

Why do you suppose they go to all the trouble of size sorting? Because SIZE MATTERS! A few tenths MATTERS!

Click to expand...

You want to be durned sure of the clearances to bore at the tightest end of the recommended fit. Rebores I've had done the shop aimed for the mid-range clearance, definitely reluctant to go as tight as possible. Even then they were very keen to stress a gentle run-in program...

Re: Gathering top end tips!!! 71 norton....

Rohan said:

concours said:

LOL, Not looking for a pissing match, just talking ACTUAL ACCURATE MEASUREMENTS, rather than "stories".
.

Click to expand...

Just looking to keeping a balanced view here.
Boring too tight can be quite destructive....

Surprised no-one has recommended breaking rings in dry.
Good and quick for race motors, but road bikes ??

Click to expand...

LOL, the dry ring thing... let's start a seperate thread for that.

Re: Gathering top end tips!!! 71 norton....

Rohan said:

concours said:

Why do you suppose they go to all the trouble of size sorting? Because SIZE MATTERS! A few tenths MATTERS!

Click to expand...

You want to be durned sure of the clearances to bore at the tightest end of the recommended fit. Rebores I've had done the shop aimed for the mid-range clearance, definitely reluctant to go as tight as possible. Even then they were very keen to stress a gentle run-in program...

Click to expand...

LOL, This is PRECISELY the point I've been attempting to make. Please, re-read my original post. A feeler gage won't lie...

Re: Gathering top end tips!!! 71 norton....

Well I measured ring gaps for all the rings and no others were 20 thou but all were between 16-18... None were at 12 thou but one was 20.

I hope it has good compression!

I took the good advice of placing the pistons in the barrel beforehand and that streamlined the process significantly. I was able to get the barrel on without any issues. I have a light coating onf engine oil on the hone so as to keep it from rusting in the garage while I am still piecing the thing together.

So far I have the pistons micced and the bore clearance is 5 thou, the ring gaps are 16-20 thou.

I was thinking that the ring gap could be ok if it was 16-20 but I guess this is too much? I dont wanna be burnin oil out of the gate! I shoulda measured gaps before I had the shop bore....

Well as an upside it looks pretty with a new coat of hitemp on it hahah If it doesnt work out I will be ready to go at it again and get it better. If it does work out I will still try and find another project to do it again. This stuff is fun.

Re: Gathering top end tips!!! 71 norton....

I just finished putting my barrel and head on after finally sorting out the main bearings.

In fitting the barrel, I made ring compressors out of a 1" wide strip of stainless steel that had been lying on the garage floor for ages (I don't remember where it came from.)
I clamped them with tie wire, and they worked a treat. It was almost too easy.

For the head, I used the rag trick to hold the pushrods in place before suspending the head over the barrel with the elastic strap that holds the rear of the fuel tank down.
I hooked the strap on to "studs" that I made which screwed into the oil feed holes (5/16-22 BSF). With the head safely suspended over the barrel, you can then go about the business of dropping the pushrods into the cam followers and lining them up with the rockers (it would have been even easier if I had used rubber bands on the rockers like Dave suggested).
Once aligned, I pushed the head down before removing the elastic strap, and then started tightening bolts.

It was much easier and less risky than doing it by the manual - ie holding the head in one hand and doing four things simultaneously with the other.
I thank the people on this forum for suggesting these ideas.

Cheers
Martin

Re: Gathering top end tips!!! 71 norton....

MFB said:

I just finished putting my barrel and head on after finally sorting out the main bearings. etc

Click to expand...

Good tips. It can be quite a juggling act to get everything back where its needed.
I've used a rope from the rafters to lower the head (and cylinders) into place. (You need rafters for this to work, of course).
Having a trained octopus would be quite helpful....

Re: Gathering top end tips!!! 71 norton....

iceteanolemon said:

Well I measured ring gaps for all the rings and no others were 20 thou but all were between 16-18... None were at 12 thou but one was 20.

I hope it has good compression!
<snip>

I was thinking that the ring gap could be ok if it was 16-20 but I guess this is too much? I dont wanna be burnin oil out of the gate! I shoulda measured gaps before I had the shop bore....
<snip>
This stuff is fun.

Click to expand...

Boring to suit the ring gap sounds like a back-to-front way of doing things - you'd want to have in writing the piston manufacturers recommended clearances to make this work.
So KNOW that that clearance would work...

I installed some (small) H*nda pistons - zero clearance to the bore.
Zero ? Yep ! If you warmed them in your hands, they wouldn't even fit.
About then you notice that metallurgy has come a long way...

Re: Gathering top end tips!!! 71 norton....

concours said:

Why do you suppose they go to all the trouble of size sorting? Because SIZE MATTERS! A few tenths MATTERS!

Click to expand...

Rohan said:

You want to be durned sure of the clearances to bore at the tightest end of the recommended fit. Rebores I've had done the shop aimed for the mid-range clearance, definitely reluctant to go as tight as possible. Even then they were very keen to stress a gentle run-in program...

Click to expand...

concours said:

LOL, This is PRECISELY the point I've been attempting to make. Please, re-read my original post. A feeler gage won't lie...

Click to expand...

Its important to note that selective matching of pistons to bore size is mostly so you (manufacturer) don't get the piston clearance too tight in a new engine - ie a big piston in a small bore. Seizure territory = in a new bike not good.
While conversely this also means there should be no small pistons in a large bore (relatively, we are talking ten thousanths" here), this only may give a slightly noisy engine - until it warms up...

Jist for clarity for folks reading here....

P.S. You won't even get the usual feeler gauges in here, micrometers and inside micrometers required...

Re: Gathering top end tips!!! 71 norton....

Rohan said:

concours said:

Why do you suppose they go to all the trouble of size sorting? Because SIZE MATTERS! A few tenths MATTERS!

Click to expand...

Rohan said:

You want to be durned sure of the clearances to bore at the tightest end of the recommended fit. Rebores I've had done the shop aimed for the mid-range clearance, definitely reluctant to go as tight as possible. Even then they were very keen to stress a gentle run-in program...

Click to expand...

concours said:

LOL, This is PRECISELY the point I've been attempting to make. Please, re-read my original post. A feeler gage won't lie...

Click to expand...

Its important to note that selective matching of pistons to bore size is mostly so you (manufacturer) don't get the piston clearance too tight in a new engine - ie a big piston in a small bore. Seizure territory = in a new bike not good.
While conversely this also means there should be no small pistons in a large bore (relatively, we are talking ten thousanths" here), this only may give a slightly noisy engine - until it warms up...

Jist for clarity for folks reading here....

P.S. You won't even get the usual feeler gauges in here, micrometers and inside micrometers required...

Click to expand...

Gee whiz, my feeler gages (all the sets I've EVER had) go down to .0015" As a final verification after all the measuring's done. .003" slips in, .004" is snug.

Re: Gathering top end tips!!! 71 norton....

Rohan said:

concours said:

Why do you suppose they go to all the trouble of size sorting? Because SIZE MATTERS! A few tenths MATTERS!

Click to expand...

Rohan said:

You want to be durned sure of the clearances to bore at the tightest end of the recommended fit. Rebores I've had done the shop aimed for the mid-range clearance, definitely reluctant to go as tight as possible. Even then they were very keen to stress a gentle run-in program...

Click to expand...

concours said:

LOL, This is PRECISELY the point I've been attempting to make. Please, re-read my original post. A feeler gage won't lie...

Click to expand...

Its important to note that selective matching of pistons to bore size is mostly so you (manufacturer) don't get the piston clearance too tight in a new engine - ie a big piston in a small bore. Seizure territory = in a new bike not good.
While conversely this also means there should be no small pistons in a large bore (relatively, we are talking ten thousanths" here), this only may give a slightly noisy engine - until it warms up...

Jist for clarity for folks reading here....

P.S. You won't even get the usual feeler gauges in here, micrometers and inside micrometers required...

Click to expand...

Tolerances... the LARGEST piston allowable by the sizes published and the SMALLEST bore yields .0033 clearance and the SMALLEST piston in the LARGEST bore calculates out to .0047 clearance. THAT is the range allowed. See? All the 'rithmatic has already been done. No guesswork.