Barrels done, head under way

Hello everyone,

Just another update on how my poor old Z13 is coming along.

After riding the old girl for three short rides, I have had to remove the head and barrels due to excessive smoking and some low compressions.

Once apart I took the barrels to my local machine shop who inspected them and said they were still standard with minimal wear and I could probably get away with a quick hone and throwing the barrels back on. I on the other hand have never had much sucess with doing that and have always ended up having to strip back down and rebore anyway. So I opted to get some new 1st oversize piston from MCG in Germany.
They arrived the other day and what a beautiful piece of art they are.
When I took them to my machine shop they were impressed with the quality, consistancy of shape, so much so that all pistons measured exactly the same, which made boring simple for them.
With the piston set came a data sheet for clearances, being 0.020mm, or roughly about 1thou in imperial talk. My machinists were concerned about the small amount of clearance, they would like to have seen 1.5 - 2 thou clearance.
I e-mailed Helmut at MCG who assured me as the pistons are coated (teflon ?) and that is all they require.
What are your thoughts on this?

At the same time I took the head and valves to my head specialist to inspect and am up for six new exhaust valves and one inlet valve, plus 3 exhaust valve guides.
I am presently waiting for them all to arrive from overseas.

Over the next week or so I will be putting my pistons/rings/barrels back together, which should be an interesting excercise. Which brings me to a question, what is the best assembly OIL to use on the bores/pistons as I don't want to inhibit any bedding in that is necessary by using something not designed specifically for that application

I have tried to upload some photos of my barrels and the new piston but without success. Will try again.....

Torque59 wrote: With the piston set came a data sheet for clearances, being 0.020mm, or roughly about 1thou in imperial talk. My machinists were concerned about the small amount of clearance, they would like to have seen 1.5 - 2 thou clearance.
I e-mailed Helmut at MCG who assured me as the pistons are coated (teflon ?) and that is all they require.
What are your thoughts on this?

I've run across this before. It's especially a confusing problem when the piston manufacturer and the OEM specs differ. Sometimes the problem can stem from the fact that the original piston was cast or forged and the new one is the opposite to the old one. Best bet is to follow the new piston manufacturer's spec since the piston was manufactured to fit your specific application.

I'm not a big fan of engine assembly lubes. What you want when you start up a new engine is a quick break in of the piston rings to seal up the piston to ring to cylinder walls and any assembly oil will have friction modifiers in it which will inhibit that requirement. Most oil manufacturers assume that as an engine builder, you'll probably take a long time (weeks maybe) to assemble an engine and then try to fire it up with no initial oil pressure and do great harm to the newly built engine, so they produce an engine assembly oil which will cling to parts for extended periods of time and compensate for the length of time it takes to assemble an engine.

My preference is to assemble the engine with whichever engine oil you plan on using. Hold off on installing the valve cover till just before the first engine start and just before you plan on the first start, pour the last liter of engine oil all over the camshafts and timing chains. Then install the rocker cover. Then prior to starting the engine, with the sparkplugs removed, turn the engine over on the starter for 5-10 20 second bursts to prelube the engine prior to firing it up. That will fill the oil galleries and pressurize the lube circuit prior to start up guaranteeing positive lubrication to your new rebuild.

Equally important to this whole thought is to reinforce the "Cleanliness is next to Godliness Rule". I never assemble an engine in any area before completely cleaning all the surfaces (tabletops, benches, ESPECIALLY TOOLS and of course all the parts to be assembled. Once you start assembling your engine, you'll be picking up items without thinking and putting things together. It's an exciting time and if you don't do this "Operating Room Disinfecting" you'll end up contaminating everything with minute debris and you may as well throw in a pail of sand into your new engine.
I've seen NASCAR assembly rooms and I respect what the intension is here. You'd swear they were operating on a patient and not a car. I fully understand their intent and I assemble parts only when I've gone through "my assembly area disinfecting procedure"

Good luck with your build. I hope these thoughts are valuable to you.

Kawboy

Thanks for your thoughts Kawboy, you have pretty much confirmed what I was thinking.
It's just nice to have confirmation your on the right track.
I used to swing spanners a lifetime ago, and your cleanliness is next to godliness routine is something I have never forgotten and still do.
I thought I would use a slightly thicker weight oil when I reassemble it as I have to wait for the head to come back, as I am still waiting for some parts to arrive.
Good idea about leaving the tappet cover off and putting oil over the cams etc and down the bores just prior to firing up, will definitely do that.
Thanks again.

I also like to "flush" the bottom end out before I start reassembly. I took the oil pan off and cleaned it out and then sprayed automatic transmission fluid around the crank to clean out any bits of debris that may have found their way down during disassembly and gasket removal. I just poke a small hole through the top of a quart bottle and squeeze, works pretty well. I use ATF because it is a thin oil and can also wick into the bearing clearances. Just like Kawboy I also like to prime the oil system after the engine is together.

Piston clearance is a matter of the piston manufacture ONLY. Cast pistons are generally fit with less clearance than forged for a number of reasons. When in conflict follow the specs on the pistons. Mine are forged and the spec was .003" clearance.