I must say, have been looking forward to this bit for a long time! When you install the pistons you know it is getting serious!
First thing is to make sure everything is clean. I washed the pistons in hot soapy water, and dried them using the vacuum cleaner in ‘blow mode’ – much quieter than a compressor. I then cleaned the bores using carburettor cleaner followed by a light coat of engine oil.
I bought Hastings piston rings with a moly top ring after researching all of the different options (cast iron, moly and chrome). Moly is short for molybdenum, which has high scuff resistance and a very high melting point. It is also quite porous, so it retains oil better than plain cast iron or chrome rings. The reality is that it won’t make a huge difference for this engine, but every little bit helps! If anyone is interested, here is a detailed explanation from Hastings.
I fitted the oil scraper rings first. They are nice and flexible which makes installing them too easy. Here are all 8 pistons with the oil rings fitted.
Next is the top rings. You need to be much more careful with these as they are cast iron, and don’t like being twisted. I bought a cool ring expanding tool which is easy to use, and spreads the rings without allowing them to twist.
The pics below show the expander with a ring installed, and then expanded. It made fitting the rings to the pistons quick and easy!
Thanks to the ring expander, the rings went in quick and easy. If you look closely below you can see the top ring has a shiny finish on its edge, and the second ring is dull. The shiny stuff is the moly treament.
Now that the rings are all installed, it is time to get down to business!
Now when it comes to ring gap alignment, there is plenty written. I have done quite a bit of reading to try and understand how important it really is. It seems that almost everyone has an opinion. Even though some of them don’t necessarily agree where the gaps should be, everyone agrees they should be staggered.
I then found a very interesting paper. An engine builder put together an engine (V8) where one bank had staggered gaps, and the other bank had all of the gaps aligned. The engine was run in on a dyno and then the engine was tested by cutting each cylinder. This was followed up by a compression test. The difference between each cylinder and bank was insignificant! The facts often challenge accepted practices.
Having read this, I still staggered the ring gaps, but I am not too fussed about it.
I coated the first piston and rings with a small amount of engine oil. Some like to drown the piston in oil, but this is not necessary, and I wonder if it may even create a bit of sludge when the engine starts. I then installed the ring compressor and also placed a piece of rubber hose over each stud at the big end to make sure they don’t damage the bore on the way down. Lastly I installed a bearing in the big end of the connecting rod and lubed the surface as well as the crank journal with engine assembly lube.
After double checking the piston orientation (they have ‘REAR’ cast into the back face), and also double checking the rod orientation, I inserted it into the bore carefully feeding the rod through without touching the bore surface. A few firm taps with a soft hammer, and it was in its new home.
I then put a bearing in the bearing cap and installed it to close off the process.
Repeat 7 more times…and there you have it!
The last job was to torque up all of the bearing cap bolts to 45 ft lbs.
A quick word on my torque wrench. I have had my torque wrench for over 20 years and it still looks like it is brand new. This is partly because it has not had a huge amount of use, and partly because the only place this wrench lives is either in my hands, or in it’s box. I was always taught that a torque wrench is a precision instrument, and should be treated like one. I will get off the soap box now 😉
For anyone who is wondering about the title….slugs is ‘petrolhead slang’ for pistons, and pots is slang for the cylinders.