Piston and cylinder assembly, Tips? Options

[TheCabinetmaker]

Doing a top end on a 1.7L. New c/p's. New heads.
The p/c assemblies seem to be quite dirty. Should I take them apart and clean and relube evetything? what should I clean them with. I read about weighing the pistons. Should I check the ring gap, or assume(I hate that word) the were checked when assembled.

This ain't my first time, but it has been a "few" years.

Thanks, Curt

[Mark Henry]

If your talking new P/C's you must clean them, that stuff is a rust protector. If used then you should hone the cylinders and get new rings.
Stock gaps are most times OK, but I still check them.

I try to get guys to balance everything, on the el-cheapo jobs I still balance the pistons.

[TheCabinetmaker]

Mark,
Yes, they are new p/c sets. What should the weight tolerances be and best way to achieve? Grinding the skirt?

Clean with soap and water, or solvent?

[914ghost]

Why would new p/c's be dirty I wonder?
If they're out of the box try some light solvent- like white gas ro alchohol. Maybe it just cosmoline, it protects the surface.
And DONT grind the skirt, that helps make the piston run straight- I dunno, pistons are different depending on who made them, you usually have to grind inside somewhere there is most material.
Also, weigh the wrist pins, if one is heavy you could stick it in a light piston (if the fit is right) to get them closer.
I don't know what everyone uses for tolerances on them, they aren't "rotating" parts so not as vital as rods / flywheel. I balance rods using a letter scale to like 0.10 grams give or take, then dynamically balance w/crank. Pistons...? Maybe1-3 grams (if at all) would make me pretty happy. Depends on how much I care about the engine.
Just my take again, you'll hear better advice.
Robert O

[Matt Romanowski]

You almost always remove weight under the crown. Some JEs suggest from the wrist pin boss. How close depends on your scale and free time. Mine are all perfect.

As for dynamic balancing, as along as the crank is balanced, all the pistons and rods are balanced, then it should all be ok. It's not like a V engine. There is a direct opposite force for everything. At least that's how one of the best engine builders in the country put it to me.

I like to clean everything with solvent. Depending where I am, I use either the tank or brake clean. Check all the clearances - end gap, skirt clearance, and eventually deck height.

Matt

[TheCabinetmaker]

Ok, we're going to clean everything with solvent, Weigh and try to balance the pistons, check skirt clearance, ring gap, and deck height.

Do we check both compression rings, or just the top one?

Thanks for the info.

[Mark Henry]

Swapping pins, the wrist pin boss and under the crown done with a milling machine. If the balance guy pulls out a drill bit for doing the backside...RUN!

I totally dissagree with Matt's buddy on crank balancing, he must rebuild straight sixes (or V-12's) for a living. Unless he's talking about the whole crank assembly, balancing the crank alone is worthless.

But if he's talking about the whole crank assembly and you do the rods and pistons, well you just did the whole engine.

I check all the rings.

[Matt Romanowski]

Mark,

This guys has done every engine known to man. One time he said something about Merlin (sp?) engines. I replied, "They make nice boat stuff." He chuckled. He was talking about about WWII aircraft engines.

Maybe I communicated wrong. The crank must be dynamincally balanced (but does not get weights put on it like a V8 crank would). The pistons, rods, and pins all have to be balanced (to each other). So yes, everything gets balanced, but not like in a V engine.

Also, you don't need a mill to lighten the pistons. Removing some metal can be done lots of ways.....but never with a drill bit.

Matt

[0396]

I built a 3.4 and my friend balance the wrist pins/rings /pistons
to with in .002 grams.

Blue Print (IMG:style_emoticons/default/wink.gif)

[TheCabinetmaker]

Stock 1.7-top end only-I'll be ok with 3 grams (IMG:style_emoticons/default/laugh.gif)

[Mark Henry]

Mark,

This guys has done every engine known to man. One time he said something about Merlin (sp?) engines. I replied, "They make nice boat stuff." He chuckled. He was talking about about WWII aircraft engines.

Maybe I communicated wrong. The crank must be dynamincally balanced (but does not get weights put on it like a V8 crank would). The pistons, rods, and pins all have to be balanced (to each other). So yes, everything gets balanced, but not like in a V engine.

Matt

Balancing a VW or a Porsche or a V8 what’s the diff???
If a customer pays for a balance job he gets a lower quality job because it's a VW or a four??

The rotating mass of any engine needs to be balanced, the stock balance on a VW or a V8 is OK for a stocker, but any hipo or high-end engine build will benefit from being balanced.
The VW engine is not a naturally balanced engine, in hipo form the balance is critical. The engine has only 3 main (not counting #4) journals to hold 4 rod journals, this is why all flat four cranks are forged. Porsche knew this was a problem that’s why the six has 7 mains (8 total) between the rods. Yes, a V8 has two rods between 2 mains but they share 1 rod journal, so that mains are closer to each other. If your talking counterweights, well any of the stroker (and most T1 stock stroke) T1 and T4 hipo engines I build will have counterweights.

I think you are confusing the fact that V8 crankshafts had many problems when they were first being designed and that counterweights were employed to elimanate one set of design problems. This has little to do with the dynamic balance, as a matter of fact if you put a VW and a V8 crank back to back on a balancer, the factory balance would be about the same on both cranks.

BTW That's a Rolls Royce Merlin engine used in Spitfires, Hurricanes, Mosquitoes and Lancaster's.