Leak Down Test (Don't Laugh!!)

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Jim does make it look easy!

I don’t have his practice or experience. I still prefer to fit pistons to rods first. Then...

If the engine is out, I use finger nails and shuffling on the bench like this:
Leak Down Test (Don't Laugh!!)




If the engine is in the bike I still prefer a stout board to support the pistons (shown below) then use piston ring clamps. I find this method utterly straightforward and fuss free...

Leak Down Test (Don't Laugh!!)
 
Fast Eddie said:
Nice meaty looking liners you’ve got in there by the way Click...
Click to expand...

Thanks for the pics. I was going to do the board with the cut slot & ring compressors trick but decided on Jim C's method, time will tell . . . . . .

Nice workshop by the way:)
 
WZ507 said:
The table below provides Otto cycle efficiency comparisons over a slightly broader range of compression ratio than shown in the above link at Victory Library. The calculation used here to generate the data table is identical to that described at Victory Library where exponent K = 1.25 was employed. Thought it might be of interest. Hope it is large enough to be legible.

View attachment 7798
Click to expand...

When it comes to compression ratios, best to think in terms of peak torque and area under the torque curve rather than peak horsepower. This is supported by Comnoz observations as well as that of Herb Becker.

According to the table referenced and taking a very simple view of the data, going from 8.5:1 to 11.5:1 theoretically yields 10% gain which is nothing to dismiss. I would expect this gain to be in peak torque.

There's more at play than just the Otto Cycle Efficiency when increasing compression ratio including the possibility of increasing the compactness of the combustion chamber, thus the efficiency of the combustion chamber (if done correctly). In theory, this should yield less ignition advance for the engine to be happy - always a good thing.
 
OK, getting close.

Just double checking, I have snap ring circlips for the gudgeon pins. These have a flat side & a curved side.

Does the flat side face out?

Does it matter which way the gap in the circlips is orientated? I have it pointing up towards the top of the piston.
 
OK, first attempt a failure:(

Had everything ready, pins in the fridge over night, had a hot air room heater on the barrels/pistons for about 30mins.

Lined everything up as best I could & started to put the first pin in, VERY tight, small taps with a hammer but it was getting tighter.

Decided to stop & regroup:rolleyes:

Went to get my hotair gun & I had loaned it to a mate!!, getting it back later today.

Going to heat the pistons in the bore on the bench with the hot air gun & see if the pins will slide in by hand, if that works I'll try again.

Used Wellseal on the gasket so might be able to reuse it?? I have one spare so might just use that!

The method Jim uses with the sockets works but everything is a bit 'wobbly', with the engine canted forward the barrels want to slide forward & there's just enough of the barrel caught on the rear sockets to keep it up.

If for some reason I can't get this to work I'll revert to fitting the pistons on the rods first ( I can use a gudgeon pin install tool to help with getting the pin in) and then use a board to hold up the pistons & use ring clamps the same as Fast Eddies pics above.

More Anon!
 
You said fridge...freezer compartment one hopes.
The heat gun is what you want to expand the alloy.
These two should make it a breeze.
 
If you still achieve no success Id try the pin in just the piston and just rod and see which is the problem.
 
OK, success sort of!!!

I heated up the piston & had the pins in the freezer and I could get the pins all the way across but there's another issue.

I've sent an email to Jim, so more Anon!
 
I'm back!!!!

Had to get a bit of 'fettling' done by Jim (gudgeon pins)

Re-cap for those who don't want to read 30 pages of my ramblings!!

I had a 920 MK3 using the Norvil conversion with the larger gudgeon pins. (done before I became the keeper of this bike)

I was having a smoking problem with the 920 & kept looking at the top end + carbs for a solution. Eventually I pulled the barrels & the pistons were severely scored and the bore was damaged. Horror pictures are in the thread!

Because of the 920 conversion with the larger gudgeon pins a simple job of putting standard pistons + barrel on was not an option for me as it would involve splitting the cases to put new rods on & once you go that far 1000's of euro's get spent as I could already hear my inner voice saying 'ah sure since you're down that far why not . . . . . .'

I started this thread to document my bumblings & Jim C. came along & offered to sleeve my barrels to 880 & supply pistons to match + machine the pistons to match the larger gudgeon pins, how could I refuse!.

Jim C. is a busy guy & the job was more complicated than he had envisioned so it took a while but I eventually got the barrels, custom pistons & custom gudgeon pins back in the workshop.

So, I just fitted the pistons & barrels today, took 3 attempts.

The piston holding tool I made from dimensions given on this forum, BUT, I should have checked the 850 crankcases as the dimension of 4 1/2" wide JUST allowed the edges of the tool to rest on the studs. I was too lazy to make another, in hindsight I should have made another wider tool as it would have made the pistons more secure. This was the reason for all the attempts, just as the barrels were sliding down the tool would slip off the studs & I had to start again!!

Jim C. and others recommended fitting the pistons in the barrel first then offering the whole lot up to the rods but I was on my own so I went with the pistons on the rods & used ring clamps.

On the last attempt, part of the oil control ring was snagging on the lip of the barrel on one side, I was able to give a little 'giggle' & it eventually went in.

Still need to put the head on & all the other bits, at least I've done that a good few times already!!!

I know you guys like pics so here you are:


LARGER DIAMETER HOLE FOR 920 GUDGEON PINS
Leak Down Test (Don't Laugh!!)


PISTONS READY TO GO!
Leak Down Test (Don't Laugh!!)


BARRELS READY TO GO!
Leak Down Test (Don't Laugh!!)


PISTONS FITTED
Leak Down Test (Don't Laugh!!)


CIRCLIPS IN & CHECKED
Leak Down Test (Don't Laugh!!)




GASKET ON
Leak Down Test (Don't Laugh!!)


PISTON HOLDING TOOL IN PLACE 'JUST' SITTING ON THE STUDS!
Leak Down Test (Don't Laugh!!)


RING CLAMPS FITTED
Leak Down Test (Don't Laugh!!)


BARRELS & PISTONS FITTED & EVERYTHING TORQUED DOWN
Leak Down Test (Don't Laugh!!)


Time for a whiskey ;-)
 
OK, looking for some advice, to goo or not to goo??

I'm going to use a standard, Andover Norton, composite (Eyelett) CH gasket. I've only ever used copper when I was running the 920 conversion, so this is new to me!

The barrels & CH have been decked, should I use some 'goo', Hylomar, around the pushrod tunnels & the oil return hole?

If no 'goo' is the 'norm', then is it recommended to completely install the gasket dry?
 
Used the search function :rolleyes: (should have done this first!!)

Put a bit of Hylomar around the pushrod tunnels & the oil return hole.

Head is on, just need to torque everything down & put all the 'bits' back on!!
 
I have used AN composite gaskets on my 850 with perfect success so far, zero weeps of any kind.

I install them totally dry and scrupulously clean, meaning cleaning the head and barrel with solvent until a white rag stays white.

Important to follow the rigorous torquing procedure it seems (after first start up, 50, 100 and 500 miles and / or until things stop ‘moving’) it amazed me how much the fasteners would turn each time.
 
Fast Eddie said:
I have used AN composite gaskets on my 850 with perfect success so far, zero weeps of any kind.

I install them totally dry and scrupulously clean, meaning cleaning the head and barrel with solvent until a white rag stays white.

Important to follow the rigorous torquing procedure it seems (after first start up, 50, 100 and 500 miles and / or until things stop ‘moving’) it amazed me how much the fasteners would turn each time.
Click to expand...
retorquing hot or cold?
 
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