Leak Down Test (Don't Laugh!!)

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My understanding was also that the early 920 kits from RGM and Norvil used Ford pistons of some kind, which were heavier than std Norton pistons. And that the larger gudgeon pin was due to this piston choice, rather than being a deliberate design feature of the kit.

Therefore, my understanding is that if you have the larger pin, you have the heavier pistons.

The best thing would be to weigh them though, and weigh any new ones you buy, and ensure they are a) close to the weight of you old ones and b) the same as each other.


However, I just read the very informative technical notes on 920 conversions on RGMs web site. Sadly, these notes are not very favourable to these pistons! Quote:

“The old (and no longer made) 920 piston was adapted from a ford cross-flow engine, it had the disadvantages of a larger gudgeon pin, excessive weight, and too much length both above and below the pin. This piston required extensive alteration before it could be used, and in its non Powermax version had a taste for self destruction. The nominal bore size for this piston at STD size was 3.188”. Thus our piston should be suitable as a replacement for a worn 920. Once arrangements have been made to accommodate the standard size pin and the bore has been honed to 3.190“/3.191”

Here’s a link to the RGM page with a lot more 920 information:

https://www.rgmnorton.co.uk/csi/1245184/f/pdf/rgm_920_kit_instructions.pdf
 
Fast Eddie said:
My understanding was also that the early 920 kits from RGM and Norvil used Ford pistons of some kind, which were heavier than std Norton pistons. And that the larger gudgeon pin was due to this piston choice, rather than being a deliberate design feature of the kit.

Therefore, my understanding is that if you have the larger pin, you have the heavier pistons.

The best thing would be to weigh them though, and weigh any new ones you buy, and ensure they are a) close to the weight of you old ones and b) the same as each other.


However, I just read the very informative technical notes on 920 conversions on RGMs web site. Sadly, these notes are not very favourable to these pistons! Quote:

“The old (and no longer made) 920 piston was adapted from a ford cross-flow engine, it had the disadvantages of a larger gudgeon pin, excessive weight, and too much length both above and below the pin. This piston required extensive alteration before it could be used, and in its non Powermax version had a taste for self destruction. The nominal bore size for this piston at STD size was 3.188”. Thus our piston should be suitable as a replacement for a worn 920. Once arrangements have been made to accommodate the standard size pin and the bore has been honed to 3.190“/3.191”

Here’s a link to the RGM page with a lot more 920 information:

https://www.rgmnorton.co.uk/csi/1245184/f/pdf/rgm_920_kit_instructions.pdf
Click to expand...

Thanks for looking into this for me. I'll get in touch with RGM & see what options I have with them.
 
You could always get the latest RGM piston,hone the 0.003 ~4 thou out of the bores and get the pistons bored out to suit your old gudgeon pins, if the bores clean up it would be by far the cheapest and quickest option, your balance factor may not be spot on but you will probably never notice.
If these are old ford escort pistons with the bowl machined off there may be a lighter, stronger pin available from an old formula ford engine.
Then you can assemble it all dry and with in seconds it will look just like your old pistons
 
splatt said:
Then you can assemble it all dry and with in seconds it will look just like your old pistons
Click to expand...
:D

Well that made me chuckle !

I’ve never tried it myself, and I don’t think a dare ever do so either, not with my own engine at least!

Whilst I can almost understand that it may help rings bed in... Surely a dry bore is gonna rip the skirt to shreads?

Years ago, I used to bed rings in by hand, using Solvo Autosol on the rings and an old piston and a lot of elbow grease. I’d do it until I could see the sharp edge of the rings had been blunted. Then clean, lube, assemble. However, it didn’t seem to make any noticeable difference!

But then again, I have built engines before and used top spec synthetic from the get go and never seemed to suffer from rings / bores that wouldn’t bed in.

More recently, to be a ‘good boy’ I use proper breaking in oil, or at least a break in additive. Can’t say I’ve noticed any differences either way.

My conclusion? My confusion!
 
Fast Eddie said:
My understanding was also that the early 920 kits from RGM and Norvil used Ford pistons of some kind, which were heavier than std Norton pistons. And that the larger gudgeon pin was due to this piston choice, rather than being a deliberate design feature of the kit.

Therefore, my understanding is that if you have the larger pin, you have the heavier pistons.

The best thing would be to weigh them though, and weigh any new ones you buy, and ensure they are a) close to the weight of you old ones and b) the same as each other.


However, I just read the very informative technical notes on 920 conversions on RGMs web site. Sadly, these notes are not very favourable to these pistons! Quote:

“The old (and no longer made) 920 piston was adapted from a ford cross-flow engine, it had the disadvantages of a larger gudgeon pin, excessive weight, and too much length both above and below the pin. This piston required extensive alteration before it could be used, and in its non Powermax version had a taste for self destruction. The nominal bore size for this piston at STD size was 3.188”. Thus our piston should be suitable as a replacement for a worn 920. Once arrangements have been made to accommodate the standard size pin and the bore has been honed to 3.190“/3.191”

Here’s a link to the RGM page with a lot more 920 information:

https://www.rgmnorton.co.uk/csi/1245184/f/pdf/rgm_920_kit_instructions.pdf
Click to expand...

Eddie, that’s Interesting reading, thanks for posting. One thing I notice is that they seem to imply that an 850 is better for normal road use.

cliffa.
 
The way I read it, a GOOD 850 is better than a BAD 920, and many 920s are not good!

But a good 920 is better than a good 850.
 
Small update.

Talked to RGM, unfortunately the only option with them is to replace the conrods or get a special bush made up. They could not recommend making the gudgeon pin hole bigger on the piston as removing materail might weaken the piston.

I rang Norvil and the only person who can advise is Les and he is only available from 4pm-5pm, I'll ring him later today.
 
Yep, dry install is certainly different and, for many folks, uncomfortable. The advantage is that the rings/bores seat/seal almost instantly. The break-in period that is typically specified for "traditional" installation is necessary because oil inhibits the metal-to metal contact that is required for seating. YES, you need metal/metal contact between the rings/bores to "wear them in." If they don't wear in, you end up with rings that never seat and an engine that uses oil. That is the reason that many builders recommend NOT using synthetic oil for break in - it is too good at keeping the metal parts apart! This is not much of a concern for dry install.

I haven't assembled an engine "wet" for probably 20 years, including my Commando, which I rebuilt in '08. All I do as far as the bores is wipe on WD 40 to prevent rust; no oil or any lubricant of any kind on the rings, and a smear, with my finger of oil on the thrust side of the piston. The WD40 is on the bore simply to prevent rust. If I have the pistons ready to immediately install, I wouldn't use the WD40 but freshly honed bores will rust almost immediately without some sort of protection. Some engine builders that do the dry method use ATF instead of WD40. But in either case, its just wiped onto the bores with a rag dampened with the ATF. In any case, the purpose is to prevent rust, NOT to lubricate anything. So a very thin application is all that is wanted.
 
What I don’t understand is why don’t modern automotive manufacturers do this?

They most definitely oil pistons and rings on assembly.

And they get filled with ‘proper’ oil from the get go. The days of 500 mile running in periods and first services on modern cars is long gone. It’s 10,000 miles to the first service and very relaxed break in proceedures these days.

So, these engines use proper oil (sometimes synthetic, depending how flash the car is), they do not use any type of break in oil, they oil the pistons on assembly. Basically they do EVERYTHING that some folk claim will lead to and oil burning monster.

But they don’t burn oil. The rings clearly seal perfectly against the bores. They work perfectly. For hundreds of thousands of miles.

Why...?
 
Fast Eddie said:
What I don’t understand is why don’t modern automotive manufacturers do this?

They most definitely oil pistons and rings on assembly.

And they get filled with ‘proper’ oil from the get go. The days of 500 mile running in periods and first services on modern cars is long gone. It’s 10,000 miles to the first service and very relaxed break in proceedures these days.

So, these engines use proper oil (sometimes synthetic, depending how flash the car is), they do not use any type of break in oil, they oil the pistons on assembly. Basically they do EVERYTHING that some folk claim will lead to and oil burning monster.

But they don’t burn oil. The rings clearly seal perfectly against the bores. They work perfectly. For hundreds of thousands of miles.

Why...?
Click to expand...

Looks like this has also been discussed on the NOC site...

https://www.nortonownersclub.org/support/technical-support-common/running-in-new-piston-rings

cliffa
 
click said:
I think you said this earlier that modern watercooled engines tend to have much tighter clearance and some guys doing reboring work who are not use to older air cooled engines don't leave the clearance required??
I'm sure a bit of wet & dry on the pistons and bore will sort everything out, or maybe a course flap wheel:rolleyes:
Click to expand...

I have noticed the smiley e –Mo- there are things you can and can’t get away with!

Rubbing the piston skirt with wet and dry to remove the high spots is a well-known method, but a flap wheel?????

You really need to hone the bore with a honing abrasive tool with something like tapping fluid oil in an electric drill-there is no need to go down to the bottom of the cylinder bore only just below where the piston rings go. I have a two stroke that was seen to this way –below the inlet port on it looks worse than you pictures since the rigs don’t go much below there –it runs perfectly happy!
 
Of course they don't recommend machining the piston out , what size is the gudgeon pin you have now ?
 
Fast Eddie said:
My understanding was also that the early 920 kits from RGM and Norvil used Ford pistons of some kind, which were heavier than std Norton pistons. And that the larger gudgeon pin was due to this piston choice, rather than being a deliberate design feature of the kit.

Therefore, my understanding is that if you have the larger pin, you have the heavier pistons.

The best thing would be to weigh them though, and weigh any new ones you buy, and ensure they are a) close to the weight of you old ones and b) the same as each other.


However, I just read the very informative technical notes on 920 conversions on RGMs web site. Sadly, these notes are not very favourable to these pistons! Quote:

“The old (and no longer made) 920 piston was adapted from a ford cross-flow engine, it had the disadvantages of a larger gudgeon pin, excessive weight, and too much length both above and below the pin. This piston required extensive alteration before it could be used, and in its non Powermax version had a taste for self destruction. The nominal bore size for this piston at STD size was 3.188”. Thus our piston should be suitable as a replacement for a worn 920. Once arrangements have been made to accommodate the standard size pin and the bore has been honed to 3.190“/3.191”

Here’s a link to the RGM page with a lot more 920 information:

https://www.rgmnorton.co.uk/csi/1245184/f/pdf/rgm_920_kit_instructions.pdf
Click to expand...

The old RGM 920 kit must be from the Wayback machine.
I have a ten year old RGM kit here . The pistons weigh the same as standard 850 and are ready to use. The gudgeon pin fits a standard small end bush
 
Surely the gudgeon pin can’t be that much bigger, otherwise the conrod would be weakened?
 
The difference is
Fast Eddie said:
What I don’t understand is why don’t modern automotive manufacturers do this?

They most definitely oil pistons and rings on assembly.

And they get filled with ‘proper’ oil from the get go. The days of 500 mile running in periods and first services on modern cars is long gone. It’s 10,000 miles to the first service and very relaxed break in proceedures these days.

So, these engines use proper oil (sometimes synthetic, depending how flash the car is), they do not use any type of break in oil, they oil the pistons on assembly. Basically they do EVERYTHING that some folk claim will lead to and oil burning monster.

But they don’t burn oil. The rings clearly seal perfectly against the bores. They work perfectly. For hundreds of thousands of miles.

Why...?
Click to expand...

It's all due to the better materials and, most importantly superior wall finish/different rings. If the ring/Cyl wall surface interface was perfect, there would be no need to "wear them in." Modern boring/honing machinery can essentially create that finish whereas older machinery did not. Also, traditional cast iron piston rings require a rather coarse wall finish/more time to properly wear in; other rings, such as moly coated rings, for example, do not. As noted, modern engines come with Syn oil as factory fill because the rings/walls are essentially "worn in" upon installation due to the capability of the boring/honing machinery and the choice of rings. The dry method came about when someone figured out/learned by accident, whatever, that by NOT putting oil on the rings, break in essentially happened within a couple of minutes. I was told it was an NHRA super stock engine builder in the late 1970's but I don't know if that's true.

However, as noted, though current factory engines are FAR better than from that era, current owners manuals still list a break in period with lesser loads for some period of milage. They also mention to expect higher oil consumption during that period as opposed to after break in.

Three examples: a current (2017) owners manual for a Dodge Challenger states max of 3500 RPM/ 55 MPH for the first 100 miles, 5000 RPM/70 MPH between 100-300 miles, and full RPM but no extended WOT throttle/85 MPH from 300-500 miles. Extended WOT - like track or maybe Autobahn use is to be avoided until 1500 miles. Surprisingly (to me), the 2016 Porsche 911 manual says not to exceed 4500 RPM until 2000 Miles! That would make me think that the factory machinery at Fiat Chrysler is better than that of Porsche! ;) Our Hyundai Santa Fe manual says not to exceed 4000 RPM for the first 600 miles. In any case, Many folks ignore all that and use the "drive it like you stole it" break in method.

This is how we broke in high performance/competition engines after building: On a Mustang dyno we would perform 3 pulls through the gears using 1/3 throttle, 3 pulls at 2/3 throttle, 3 at 3/4 throttle and two at WOT. The engine was then "broken in" and there were no restrictions on engine use from that point on.
 
splatt said:
Of course they don't recommend machining the piston out , what size is the gudgeon pin you have now ?
Click to expand...

Still have to take the pistons out & check but I was told they have a 13/16 pin
 
Got this from Norvil re: using a composite gasket with the 920 Norvil conversion:

The answer to your question about the gasket over lapping the bore -
yes but the pistons are machined on the top outside to miss it like we
said before.

So, they confirm it does overlap into the combustion chamber!
 
I talked with Les today from Norvil.

He has confirmed he has 920 +20 pistons in stock with 13/16 pins.

I've contacted Pete Lovell to ask a few more question about getting this work done. Norvil use him for machining work and I believe Andover Norton.

Does anybody on this forum have any experiences dealing with Pete L.?

In the next few hours I hope to take the pistons off & check the size of the pins.

I also plan to check the cam & have a good look around the sump to see if I can find any 'bits'!!!
 
MexicoMike said:
The difference is


It's all due to the better materials and, most importantly superior wall finish/different rings. If the ring/Cyl wall surface interface was perfect, there would be no need to "wear them in." Modern boring/honing machinery can essentially create that finish whereas older machinery did not. Also, traditional cast iron piston rings require a rather coarse wall finish/more time to properly wear in; other rings, such as moly coated rings, for example, do not. As noted, modern engines come with Syn oil as factory fill because the rings/walls are essentially "worn in" upon installation due to the capability of the boring/honing machinery and the choice of rings. The dry method came about when someone figured out/learned by accident, whatever, that by NOT putting oil on the rings, break in essentially happened within a couple of minutes. I was told it was an NHRA super stock engine builder in the late 1970's but I don't know if that's true.

However, as noted, though current factory engines are FAR better than from that era, current owners manuals still list a break in period with lesser loads for some period of milage. They also mention to expect higher oil consumption during that period as opposed to after break in.

Three examples: a current (2017) owners manual for a Dodge Challenger states max of 3500 RPM/ 55 MPH for the first 100 miles, 5000 RPM/70 MPH between 100-300 miles, and full RPM but no extended WOT throttle/85 MPH from 300-500 miles. Extended WOT - like track or maybe Autobahn use is to be avoided until 1500 miles. Surprisingly (to me), the 2016 Porsche 911 manual says not to exceed 4500 RPM until 2000 Miles! That would make me think that the factory machinery at Fiat Chrysler is better than that of Porsche! ;) Our Hyundai Santa Fe manual says not to exceed 4000 RPM for the first 600 miles. In any case, Many folks ignore all that and use the "drive it like you stole it" break in method.

This is how we broke in high performance/competition engines after building: On a Mustang dyno we would perform 3 pulls through the gears using 1/3 throttle, 3 pulls at 2/3 throttle, 3 at 3/4 throttle and two at WOT. The engine was then "broken in" and there were no restrictions on engine use from that point on.
Click to expand...

Interesting info. hopefully sooner rather than later I'll be running in my sorted barrel & pistons/rings so I'll be facing a decision!!

Some of those TV programmes 'How do they do it' type format have looked at different car & motorbike manufacturers. The one thing I took note of was each & every car & motorbike, after assembly, got put on a rolling road & they 'hammered' the engine up & down the gears to ensure the engine was performing correctly. The clips I looked at seemed to really give the engine a complete workout, red lining in each gear. Not sure if this is typical but if this is done to all engines, it has already had a type of run-in done. Don't know what oil they use for this process?
 
click said:
I talked with Les today from Norvil.

He has confirmed he has 920 +20 pistons in stock with 13/16 pins.

I've contacted Pete Lovell to ask a few more question about getting this work done. Norvil use him for machining work and I believe Andover Norton.

Does anybody on this forum have any experiences dealing with Pete L.?

In the next few hours I hope to take the pistons off & check the size of the pins.

I also plan to check the cam & have a good look around the sump to see if I can find any 'bits'!!!
Click to expand...
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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