Thread: To lube or not to lube? - pistons on re-assembly during rebuild

I always put plenty of oil on the pistons and rings during assembly.
It makes assembly much easier and the piston usually slides out of the ring compressor and into the bore in one go.


Paul

You need to heavily oil underneath the oil ring down the skirts with only a moderate oiling around the compression rings otherwise its going to blow smoke at startup and foul plugs.

Also pre oil the bores with a nylon rag, not cotton or you will end up with fibres everywhere.
Only oil it with a running in oil.
If you have too much oil around the compression rings, it can hydraulically load the rings and put a little too much pressure on them untill they pass it out.

Make sure you manually prime the oil pump first before starting. This will allow the oil jets to squirt oil onto the bore during cranking and use something like Nulon L90 on all the bigend and main bearings and cam lobes etc.

You shouldnt need to hold it at 2000rpm at startup and when the engine is cold, definitely not. Always let it warm up by varying the revs a bit but dont let it idle for any length of time.
AFAIR, the ZF is OK until its actually been put into gear, then it can become a problem, but it depends on how old the ZF is and if its had the forward clutch mod done to it to stop it pressurising and blowing the clutch. Might be worthwhile looking into this while you have the engine out and seeing what needs to be done.

Cheers

Andrew.

There are a thousand different ideas when it comes to setting up engines etc. When I was racing 2-strokes we used to run teflon coated pistons to reduce run in time and we would hone to a polished finish and not fit uber tight pistons. The motors went well and lasted longer while everybody else was running tight and hatching.... anyway....

What I would do it run some thin oil over the bores, skirt and rings for start up so that its lubed - the piston shouldn't contact the bore which will happen if it is dry. Don't rev it when you start it, wait until the oil gets through the engine - a dry engine will just get destroyed! Run the engine in under load to make everything bed in, don't do it with revs and no load - take it out and drive it.

Also, I would have to go through my archives, but I believe that reving the ZF in N will damage it. You cant do that with this specific transmission.

i lube pistons prior to insertion..

I use a light film of oil on the bore and the piston (and pretty much everything but mating faces that need to be sealed up)


what changes is the oil I use.

If its a same day build (start the build, finish and start inside of 10 actual hours) I use a light oil

If its going to be a protracted affair I use a thicker oil that will hang around.

Im also on net with the not running in at no load... 2-3 minutes with no load to check it for leaks and unusual noises and then get it out there and working a little.

Theres plenty of opinions on how to do it and WOM reports on sucess for the differt methods, look em up, find whats suitable for what youve done and run with it.

You certainly do need to oil the pistons on assembly. You should also make up a pre-oiler device using compressed air to force oil through the galleries and bearings after assembly and before start-up. Camshaft grinders/manufacturers usually recommend the lobes and contact faces of the followers on new/reground items be painted with a moly lacquer and run at around 2000rpm without stopping for about 20 minutes to bed in the new surfaces.

Unit construction engines, no separate head and block, are normally put together using Vaseline on the pistons and rings but this is for assembly purposes not just for lubrication.

Originally Posted by Brian Hjelm

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Camshaft grinders/manufacturers usually recommend the lobes and contact faces of the followers on new/reground items be painted with a moly lacquer and run at around 2000rpm without stopping for about 20 minutes to bed in the new surfaces.

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ditto.

Always did this with new cam/lifters on any flat tappet engine.
With the engines I used to build, we actually made a cam running in rig as I and the bloke I worked with didn't like the idea of running a new engine at 2000RPM+ for 20+ minutes without load.
The idea of the speed + time ensures the lifters rotate properly as the cam and lifters bed. The cam face is ground with a taper on it, with the lifters having a corresponding radius ground on them at (hopefully) the same angle.

Many thanks folks for the helpful advice gents!