Leak Down Test (Don't Laugh!!)

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baz said:
I would use extreme caution dealing with norvil , especially buying pistons he's not unknown to send out the wrong type/size/mismatched pistons.
Then he will blame you for not fitting them properly and if you try to send them back he will claim his "piston man" is on holiday and unable to check the size/type of piston etc etc etc etc .
Funnily enough he sells pistons on eBay that are almost as bad as yours !!
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Not something I want to hear!!!

My only low-ish cost option, if I want to keep the 920 barrels, is getting +20 oversize from Norvil. I'm unaware of anybody else selling these?
I might end up dealing with Pete Lovell and I'll ask him to supply the pistons & rings + rebore & match them up.

I could change it back to a STD 850 BUT because the concords have been machined to accept the larger gudgeon pin I would have to get the complete engine stripped, remove the conrods and replace with standard BUT if I was going down that far I'd look at other alternatives Jim S. etc.
 
Why not go RGM but instead of boring out their pistons for the bigger pin instead bush the con rod for their smaller pin.
 
I'm just not getting a good feel for the 850 composite gasket cantilevered in over the 920 holes and flapping in the breeze. Even tho the pistons are machined smaller at top, it doesn't seem like good engineering.
Are the pistons machined so as to avoid interference with the stock 850 head?

Also, just how high above the deck did your munched pistons rise?
 
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OK, got one piston off BUT the battery in my digital vernier is wasted & the backup is also toast:(

I do have an old used micrometer screw gauge & it reads 20.35mm which is 13/16th's so I do have the older, heavier pistons which use the 13/16th gudgeon pins.

So, my options are limited.
 
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kommando said:
Why not go RGM but instead of boring out their pistons for the bigger pin instead bush the con rod for their smaller pin.
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The logistics of getting a half stripped engine to an engineering shop + finding an engineering shop I would trust has removed this option off the list
 
worntorn said:
I'm just not getting a good feel for the 850 composite gasket cantilevered in over the 920 holes and flapping in the breeze. Even tho the pistons are machined smaller at top, it doesn't seem like good engineering.
Are the pistons machined so as to avoid interference with the stock 850 head?

Also, just how high above the deck did your munched pistons rise?
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I also do not think this is a very elegant or wise engineering solution. The bit of the gasket that get compressed is now hanging over the edge of the bore! Maybe it works but it's not for me.

I didn't take this measurement before I took the barrels off. I did put a steel ruler across the deck & it looked like the dome of the piston was just the height of the deck & around the edge of the piston was machined to be below the deck height. Not sure if this answers your question. Remember you are dealing with a non engineer :)
 
It's absolutely freezing outside at the moment, even with a heater in my garage it's too cold:( so that's me finished for the night.

Most of the rest of the stuff on my list is visually checking things like the cam, crank, rods, sump etc. etc.

Hopefully it will be a bit warmer tomorrow night;)
 
1/8th '' may be a bit much as I haven't seen rgm pistons, someone thought it was ok to machine out of the rod eye.
I did see some high performance kent crossflow pistons on the net if that is what the used
Bushing rods in place will more than likely bring tears eventually
 
Hi Click , have a call to Pete Lovell , and explain your problem , with him , he is a perfect bloke and I think he could help you , find him under Pete Lovell development on the web ......
 
OK, was just talking to Pete Lovell, really nice guy.

He had a look at the pictures of the pistons & his initial reaction is that it has been happening over a long period of time & shows signs of cold seizure. He feels if it was a hot seizure he would see different types of damage. He is going to show the pictures to somebody else for another opinion. At this stage all this is academic but it might be nice to know.

He has also seen similar issues with bikes being left for long periods and the pet cocks leak from the petrol tank, washing the bores of oil & diluting the oil. I don't think my pet cocks are leaking but I'll double check just in case.

Pete can take that barrels and sort everything out for me, rebore, oversized pistons etc.

I just have to identify the cam I have in the bike, he suggested measuring the 'lift' of the cam with a vernier calliper, reminds me I have to get batteries!!

Do you guys know of any other method for identifying a cam in situ? Any markings to look out for?

I'll take some pics of the cam later tonight & post them here.

"It takes a village to raise a Norton" from the ashes :)
 
Great, sounds like Pete’s your ideal ‘one stop shop’ !

Take some pics of any numbers you can find on the cam and post them, I’m sure the collective on here will ID it for you.

Why do you need to know that anyway? So long as you copy you old pistons you shouldn’t have any valve to piston clearances to worry about.
 
Fast Eddie said:
Great, sounds like Pete’s your ideal ‘one stop shop’ !

Take some pics of any numbers you can find on the cam and post them, I’m sure the collective on here will ID it for you.

Why do you need to know that anyway? So long as you copy you old pistons you shouldn’t have any valve to piston clearances to worry about.
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I think Pete just wants to be sure about clearances. I've asked him to skim the deck of the barrels. I'm also going to send over the head so he has all the elements involved.

Might be a bit of overkill but I'd rather ere on the side of caution!!!
 
Sounds like you've found the right guy for the job! :) As you noted, re the cam it's best to be sure about what's in there! There can be a piston/valve clearance issue with aftermarket work where it is sufficient for general riding but under heavy load (heat) the clearance goes away. Sometimes people ASSUME the piston/valve clearance using aftermarket parts/engine changes will be ok based on expectations/specifications and they never actually check it. "Bang" can be the result!
 
MexicoMike said:
Sounds like you've found the right guy for the job! :) As you noted, re the cam it's best to be sure about what's in there! There can be a piston/valve clearance issue with aftermarket work where it is sufficient for general riding but under heavy load (heat) the clearance goes away. Sometimes people ASSUME the piston/valve clearance using aftermarket parts/engine changes will be ok based on expectations/specifications and they never actually check it. "Bang" can be the result!
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+1
I always assemble engine & ALWAYS check piston /valve clearance with clay/plasticine -I very rarely get a bent valve-and I have had a few in 2 million miles ...............
 
If you’re sending him the head, and he’s supplying new pistons, then I would ask him to open out the head to suit the bore and machine the pistons accordingly.
 
Fast Eddie said:
If you’re sending him the head, and he’s supplying new pistons, then I would ask him to open out the head to suit the bore and machine the pistons accordingly.
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OK, I sort of understand what you are saying. What advantage would this have? (sorry if this seems a very basic question but I'm a very basic guy when it comes to stuff like this!)
 
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