Sunday, February 7, 2016

Pistons In

In the previous post, I spent quite a lot of time and energy making sure all the engine parts were scrupulously clean, and having already installed the crankshaft, it's time to get the pistons sorted.



Why, you might ask yourself are all the pistons sat in a tray of oil... well it all started a few months ago back in this post here. This is where I first realised there was a quite a large weight discrepancy across the four pistons, which was probably the main reason the engine vibrated so badly. Due to this, the pistons along with a few other parts were sent off to a machine shop to be balanced.

When I got them back, they were in a disappointingly dirty state, I say disappointingly as I'm sure that when I dropped them off, they mentioned that everything would be cleaned before they gave them back. Problem is though, I'm not absolutely sure if they did say that or whether I just imagined it, so I didn't challenge them about it.



Most of the debris on the pistons seemed to consisted of very small particles of metal, probably left over from them grinding metal away in order to make them all the same weight. I think it's safe to assume it's going to be pretty abrasive stuff and not the kind of thing you want to have inside an engine. So to make sure that everything was clean, the pistons, conrods and caps were all thoroughly scrubbed in a tray of red diesel several times over. Each time with fresh diesel.





After they had dried out they were of course totally de-greased, naked as it were and now vulnerable to going rusty. As it's the dead of winter here at the moment, the air is rather moist to say the least and also I knew at the time, it would be a few months before I would get round to installing them. As, I didn't want to leave them naked in such a moist atmosphere for that long, I had a hunt around for my WD40, which of course is always missing, so I took the decision to dunk them in some oil to protect them from both rust and dust. As a bonus, it leaves absolutely no doubt that the gudgeon pins are now well oiled!

And there they sat until about a week ago, when they were lifted out and left to drain, wiped down, given another little slosh about in red diesel and blasted with brake cleaner to make sure they were clean and de-greased once more.


Opening a new packet of bearings, all big end running clearances were checked, and found to be okay. This post also details why it's important to get the correct piston in the correct hole, which was a faff on at the time, but was very good experience.



And all that brings us to now; The actual installation of the pistons. Of course just prior to installation everything was cleaned one last time with brake cleaner and compressed air as they had been sat around on a shelf for a week collecting dust.

The last thing to make sure of is that the big end journals are clean also, so they were given a quick squirt of brake cleaner and a wipe and blasted with air to remove any dust. I always make sure the crank journal I'm working on is positioned in the 'bottom dead centre' position to avoid hitting it when the piston is inserted.

After a considerable amount of wasted time searching for my piston ring compressor, I was finally ready to insert the first piston.



Making sure the rings and the bore were well oiled, I mounted the piston in the bore. As for ring gap alignment, I've read a lot on the subject and there are many different thoughts and ideas, ranging from 'it's really important' to 'it's utterly irrelevant'. Even though I'm leaning towards the 'it's probably irrelevant' end of the spectrum, I still chose to arrange the gaps 180 degrees apart in line with the gudgeon pins anyway.



I find that it's possible to shove the piston in place with just my fingers rather than tapping with the butt of a hammer. Once in the bore, it was slid down and carefully mounted onto the crank. I'm ultra paranoid at this point not to bash the big end into the crank journal. Then it's just a case of putting the cap on and torquing it up to the required 37lbf ft which is 50Nm.



Incidentally, I loaded the bearing surface with engine assembly lube prior to installing the piston and the cap, also I lubricate liberally throughout with oil. It's worth mentioning also that as the bolts had been de-greased with brake cleaner, the threads needed oiling again prior to use to ensure the correct torque can be achieved.

Steadily working across the engine the job was soon done, which was a shame really as it turned out to be some very enjoyable Sunday morning 'father and son' time.



One final check that all the bolts were torqued up correctly and it's a done deal.



Ironically it's almost exactly a year ago that I was putting these self-same pistons in this self-same engine. Really wish I'd weighed them beforehand!!



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