Fixing poor leakdown, Cyl 1 leaks at 50%, rest are cool. Options

[VaccaRabite]

So, at the Sterling meet I did a leakdown test on my motor, and found a problem with Cylinder 1. 45% leakdown, but 120 lbs of compression. Was tempted just to let sleeping dogs lie, but pulled the head off.

What was going on was clear as soon as we did that, the head was not totaly sealed to the cylinder, off by a very small amount. Instead of having the head recut, I decided to try and lap the two of them together.

So, last night I hand lapped them, using ground graphite to check for even contact. I got good contact after the third round of hand lapping (lap, clean, check).

Now I need to get the jug back on the block. I have a ring compressor on the piston, but I can't ficgure out how to get the head back on. Do I have to take the piston head off the rod?

If so, how do I get it off. It looks like that tis a spring keeper that needs to be removed. Is there anyhting on the rod the needs to be loosened before I can pull the pin out to remove the piston head?

Obviously, if there is a trick to getting the jug back on without pulling off the piston head, I'd like to do that.

Zach

[Jake Raby]

Or, I suppose I could buy a .010 shim to bring the shorter cylinder up, which is what I probably need to do.

No!!
Thats half assed!

You MUST have equal cylinder lengths and equal case decks.. Adding a shim will tweak the head when the engine fires up and expands...

Sure, feel free to post on my forums as well.

[VaccaRabite]

Well, I just put the cylinders back on, put the head back on, and re-leaked it.

No change. Still 70% leak on No1.

I guess I am going to start tearing down the case to get it decked. I've checked everything else. I think.

To add insult to injury, while putting the #1 cylinder back on it slipped out of my fingers and I broke three fins (oily fingers from lubing the piston to help it slide in).

I am utterly demoralized right now. I so thought I would have this licked today. Instead, I have managed to make everything worse.

Zach

[Jake Raby]

Welcome to the world of mechanical manipulation.

Try it everyday, all day...

And people wonder why I am so intense...

[VaccaRabite]

Do I need to replace the cylinder? If you added up the broken fin pieces it added up to 5 inches of broken fins. 3 inches from 1 fin, 1 inch from the 2 other fins.

Zach

[Dr Evil]

New cylinder time (IMG:style_emoticons/default/sad.gif) I am impressed with your perseverance on this, Zach. I am now more free to give you a hand and will be seeing you in a few hours so we can talk.

[degreeoff]

Hey Zach,

Remember I told you I have that case laying around?Well I will give it to you and ask for a small donation of $100 to buy my rods crank and light flywheel to go with it. There are already oversized bearings on the thing to match the case which was line bored . The whole assembly only has a couple thousand miles on it. Just a thought.

Josh

[root]

Zach,

Real sorry about the cylinder drop! Shit happens!

For what it's worth,
in my eye's you are the Great "CHILI GOD" of Eastern Pennsylvania! (IMG:style_emoticons/default/chowtime.gif)

Keep at it you'll get there (IMG:style_emoticons/default/aktion035.gif) .............wish I was closer to help!

root

[Jake Raby]

Yep, that cylinder is toast..

[scotty b]

(IMG:style_emoticons/default/sad.gif) Damn........

[Dr Evil]

I got him fixed up. I gave him 2 cylinders (so if he drops one he is still ok (IMG:style_emoticons/default/poke.gif) ). Now he just has to have them punched out and then he can fool with this some more.

[scotty b]

Damn cool (IMG:style_emoticons/default/aktion035.gif)

[Brando]

Glad you're on the right path now (IMG:style_emoticons/default/smile.gif) Things will go together so much easier when the case's measurements are all exact and equal.

Well, I just put the cylinders back on, put the head back on, and re-leaked it.

No change. Still 70% leak on No1.

I guess I am going to start tearing down the case to get it decked. I've checked everything else.

[VaccaRabite]

Yup, got some used jugs from Mike, and a dial guage to really take accurate readings when I go back to measure deck height. I am only going to get one of them punched out, and return the unused one, once I get this puppy sorted.

I am going to be checking out day care places after work today, so I will probably drop the cylinder off to the machine shop tomorrow after work. I am also going to have them make sure that the cylinder mating surfaces are both perfectly square to each other.

Just to be sure, when I ask for the cylinder to be bored out, I want them to bore it to 96mm, right? I think thats right, but better to ask first. (2056 engine). Is there anything special that I should be asking them to do while they have the jug?

Zach

[r_towle]

Bring the piston that you will be using in that cylinder to the machine shop.
Read the specs on the rings, and the piston to determine the proper bore (clearance) for that piston and ring set.

Then you will know the bore dimension.
Cylinders are bored for specific pistons, not generic.


rich

[VaccaRabite]

THANKS!
I did not know that.

Zach

[davep]

Perhaps Jake will chime in on this for the definitive answer. He uses very specific piston to cylinder clearances that depend on the specific cylinder and specific piston.
For boring out the cylinder I understand that the cylinder MUST be clamped in a fixture just as it will be on the engine; that is, the cylinder will be clamped with equal force to what it sees between the case and head. Apparently there can be a small amount of warping of the cylinder when it is clamped as opposed to when it is sitting free. Thus the cylinder must be clamped when it is bored so that it remains perfectly cylindrical when it is installed on the engine.

[scotty b]

Probably would be a god idea to have BOTH of the cylinders for that side trued up and assured they are both even with one another. Little more $$ but it would let you know that, THAT will not be an issue upon reassembly. Remember, you still haven't solved the initial blow by problem (IMG:style_emoticons/default/sad.gif)

[Twystd1]

You will also need to know what plateau finish to put on the cylinders for your specific ring pack.

Or hopefully your machinist knows the right finish.

Even if you take the piston with you to show the machinist.
Does your machinist know what clearance the piston to cylinder should be...????

IMHO... YOU need to know this stuff before you see the machinist.

Personally, I have all my cylinders bored and honed in boring jig that is torqued to about 60 Lbs. for boring and 35-40 lbs for honing.
(SOMETIMES CALLED A HONING OR TORQUE PLATE)

This are basically a 1.5 inch thick plate of aluminum with the center milled out to access the cylinders. There is plate at the top AND the bottom of the cylinders held together by 4 hardened pieces of all thread. Then torqued to a given spec. Before any machining AND measuring takes place.

I have different plates for different bores. (Like big bores 101' 103s etc.)

If ya want to do this nats ass..... It's a good place to start.

And I would think that most GOOD aircooled machinists also do something along those lines. And have the plates available.
Cause they aint cheap to make for a one time dealio. (Time consuming)

Also... It looks like you are going to incorporate the existing "Used" rings on your pistons.
Have your machinist CHECK the rings closely for both circumferential wear and also the top edge of the top 2 rings.

If they aren't close to perfect. They MAY not seat well on a new surface.
Then again... They may work just fine.

I use new rings on fresh cylinders. PERIOD.
They are cheap insurance for good leakdown numbers and and low oil consumption.

Then again... I'm a nut case that way. Do it right..... ONCE.

Clayton
Cheers,

[VaccaRabite]

I just dropped Cyl 1&2 and piston 1 off at Air Cooled Racing. I could not get ahold of the local guy at Bug World - he is really part time these days.

Anyhow, Steve at Air Cooled was very cool, and we ended up talking for about an hour as he showed me all the stuff he was working on at his shop. If you happen to be in the big GT-headlight group buy, I saw the kits. VERY nice!

So, the cylinder should be punched out in 2 weeks or so. I asked him to bore out the new cylinder, check the rings on the piston to be sure they were still good to use, make sure the new cylinder was squared on both mating surfaces, and cut the "new" cylinder to the same height as the #2 cylinder.

There are several VERY NICE 914s at Air Cooled. He is already getting his stuff ready for the Hershey meet in April.

Zach

[VaccaRabite]

I am impatient. I want to get back to work on my engine.

I guess I'll go out and work on my wiring instead.

Zach