Being new to the engine rebuilding game, it didn't occur to me that the piston and rings shipped as they do to protect them and that they need a thorough cleaning before use... thanks for the explanation.
Sorry for not explaining myself, I'm busy and I knew Geoff would be along - I just wanted to put the brakes on before you started bolting it together as is. Is there cross hatch pattern in the barrels or just the photo making it look like there isn't?
^ Definitely add this to your check list, they do look very very smooth from the photo. If I were you I would try and switch your way of thinking round. Just because it is new does not mean it is any good, or possibly even better than what you had. So each new part still needs cleaning and inspecting with a critical eye before you incorporate it into your engine. Sounds a bit depressing, but its the route to a longer lasting build.
They are "assembled in the USA" in for some taxation reason. I.e slapped together and put in the box.. they are of course made in China to usual standards. Dont snap the cast iron piston rings as you take them off to check them..
Mine weren't. Barrels, pistons, pins, spiral locks and rings were separate. All from the same supplier in the same box from the USA.
Rebuild has started today. Removed old pistons and barrels to find one of the gudgeon pin circlip had partly destroyed itself taking part of the piston with it. Trial fitted the new 1911cc pistons and barrels. With the same shims as before, getting a deck height of. 35mm. Using 54cc for the combustion chamber size, compression ratio is 9.5:1 1mm deck height would bring it down to 8.7:1. Am I heading in the right direction?
Correction...deck height is 0.88mm which brings compression down to 8.8:1. (I read the wrong number on the feeler gauge)
Good to aim for about 1.2mm deck height. What CR would that get you to? Lucky escape with the clip, This one had a sump full of aluminium and steel grinding paste. Both clips were fitted in the same end. It only did a few hundred miles.
1.4mm deck height gives 8.3 CR. in theory, a +0.5mm shim would give me 1.38mm deck height to give 8.4 CR. (and I can get them from Heritage)
Those wire clips are really horrible, circlips with the split top or bottom or better still spiral locks for the win.
Sorry, missed this. 0.75mm shim would be better (but special order from Heritage), 8.4:1 CR might be too high and you'll possibly have to use higher octane fuel, although the tight deck helps and you'll probably get away with it.
I've got 0.5mm on order and I have two set's of 0.2mm shims in my garage. Is there any obvious reason why I can't combine the three shims to give 0.9mm? Brings the CR down to 8.3:1
You should only fit one shim; stacking them would give the thickness you want but there would probably be an oil leak due to the multiple joint faces. If a single 0.5mm shim gives a 1.38mm deck and 8.4:1 CR it should be okay but if it pinks use 98/99 octane fuel. It's difficult to give exact CR numbers, every engine is different and there are many variables but basically the higher the CR the more efficient the engine will be, but at a certain point gains are reversed and theory deviates from practice.
Before you drive yourself crazy trying to achieve the 'perfect' shim - its not clear from your post above if you have assumed this volume or measured it. If its assumed then you may find small changes in this makes a greater difference than the shims!
Challenge with shims is getting a 1mm thick one as they are all out of stock just now. I know it's far from ideal, but I may have to use two 0.5mm shims and hope that it doesn't leak oil. The volume of the combustion chamber is from web search (waiting on confirmation from AMC via Heritage). Also booked the hire of the measurement tool from Cool Air in case Heritage come up blank.
