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

[Twystd1]

Man..... The Capt. nailed it.

Clayton

[jaminM3]

In the Jake Assembly video he installs the piston down into the cylinders and comments that the Type 1 guys like to install the cylinders down onto the piston.. (IMG:style_emoticons/default/confused24.gif)

[So.Cal.914]

I don't think it really matters which way you install them as long as you are

careful with the rings. I have always installed the jug onto the piston. But in this

case, in his situation I would put the jug onto the piston and leave the wristpin

alone.

[Katmanken]

Done it both ways. You can slide the cylinder onto the piston attached to the rod if you have one of those steel strip ring compressors. I bent one up from a steel strip but you have to unwrap it from between the studs when you remove it.

I personaly like putting the piston into the cylinder with one circlip in place and pushing the con rod into the assembled piston and rod end.

Seems like the last one I did had NPR cylinders which had an inner bevel at the base of the cylinder so the cylinder could compress the ring as you slipped it onto the piston.

Ken

[DNHunt]

I've done it both ways. I find getting the wrist pin retaining clips in the most challenging part so I usually install the piston on the rod first so I have as much room as possible for the toughest procedure. Pistons with short pin heights are really tough to get on the rods if you load them first. Circlips (KB retainer) and wirelocks (JE retainer) are really tough without room. Stock not so bad.

Dave

[VaccaRabite]

So, here is what I ended up doing.

I took out the circlip on the outside end of the cylinder pin, leaving the one in place facing the #2 jug. I used a small flatheaded screwdriver to start pushing the pin out, and then a pair of 90degree angled needle nosed pliers to finish pushing the pin out (pushing out the pin towards the open side, obviously).

I pulled the piston off, aligned the rings properly, and put the piston in the jug, and then put the piston and jug back on the engine. Went back on fairly easy.

Then I realised I had forgotten to put the little spacer ring between the jug and the block, so I got to take the piston off again to put the spacer back on.

The piston ang jug are back in place, and I just need to fix the bad helicoil on the #2 spark plug before I replace the head. Trying to decide if I want to do the time cert myself, or farm it out to the bug shop down the street.

Zach

[Jake Raby]

Typically any leak at the sealing surfaces will effect the future ability of those surfaces to seat in the future, sometimes lapping doesn't cure the issue..

This sounds like it may be one of the cases like we are seeing frequently these days that have a collapsed register, needing mill deck work to remedy the problem..

The GA cases are the absolute worst.

[VaccaRabite]

Typically any leak at the sealing surfaces will effect the future ability of those surfaces to seat in the future, sometimes lapping doesn't cure the issue..

This sounds like it may be one of the cases like we are seeing frequently these days that have a collapsed register, needing mill deck work to remedy the problem..

The GA cases are the absolute worst.

Collapsed register?
Sorry, I don't know what this is yet. (learning every day)

Zach

[type47]

for the purposes of a quick (not necessarily accurate....oh, Cap'n..) reply, i think the register is the opening in the case what the cylinder fits into. i would have called it the "hole in the case". register sounds more....... official

[Twystd1]

yup

[DNHunt]

I think Jake has cases routinely decked now so every part of the cylinder register is equal distance from the case parting line. I think with kits the builder is responsible for this. This leaves no irregularities that affect the seating of the cylinders to the case. As important, all cylinders start the same distance from the centerline. If the cylinders are clean and the same height, the deck will be the same and if the sealing surface of the heads are equal, it should seal better. It removes a variable. Spending a week with Jake taught me it's all about reducing variables and getting things clean. The hobbist can control some of this but, not all. Jake's remove some of the variables especially regarding the combination of parts.

Dave

[Jake Raby]

Today with most cases being over 30 years old we have noted that the cylinder seating areas of most all cases have shifted creating irregularities that position the cylinder unevenly. This makes for uneven deck heights and uneven cylinder head clamping loads that can make for head leaks.

Today we deck every single register on engines we build and have a variance of 1/2 of one thousandth for this critical aspect of the engine blueprint process. I have seen some cases that have a .020 difference in cylinder seating surfaces and to make it worse many of them are collapsed in the center of the registers. All it takes is .005 or less to cause a head/ cylinder leak...

FYI- GA code cases are THE WORST about this...

The 2008 engine kit program is being refined currently to include the necessary case machining to eliminate this problem for kit builders.

[scotty b]

Jake the area that was leaking on Zach's engine was on the inside of the cylinder and was an area about 3/8" wide. seemed to me to be very little leakage but enough to cause a loss in compression ( and leakdown ) that is why I told him to lap it. Being that it lapped out fairly easily would you still suspect a deformed register?

[VaccaRabite]

Well, tonight I re-leak downed the cylinder and the lapping I did back in October had zero effect. No worse, but no better.

How do I fix it?

How do I test to figure out what the actual problem is?

[Dr Evil]

Take the engine to your machinist and have them check the measurements. It will be cheaper and easier in the long run. The cylinders have to be checked and the head has to be checked so that it can all be made true.

[Dr Evil]

OK, I had more than a second to think on this and here are some things you can do to help effect your repair:
- With each piston on that side at TDC measure the distance from the top of the piston to the top of the cylinder and compare.
- Do you have base gaskets on both cylinders? You can shim the cylinder that has the lower piston to cylinder top clearance.
- If you check the cylinder top to piston clearance and everything is cricket then you need to have your head worked on. It can be fly cut to bring the levels within spec. I dont remember, did you check the cylinder to make sure it was cool? I ask because, well, you know (IMG:style_emoticons/default/dry.gif) Do these simple tasks and get back with the measurements.

[VaccaRabite]

No gaskets at the base of either of the cylinders. I'll be pulling the head maybe tomorrow.

How can I get an accraute measurement without the cylinder moving with the head off?

Zach

[Dr Evil]

They make special tools for this....but you can just put a deep socket on two of the corners of the cylinder, catty corner to one another and hold them down with the nuts. You get the idea, I am sure you can make it work. No base gaskets, eh? Hmmm. This may be a good sign as it gives you some wiggle room to move the shorter cylinder up to the hight of the taller one.

[type11969]

Drop a straight edge across the cylinder tops too. Careful when tightening the socket on the head stud, you can crack a fin if you torque it down too much. I've used this method before but I question how accurate it is considering you cannot get the cylinders properly torqued to the case this way.

If a register is collapsed and a cylinder is sitting on an angle the case will have to be decked. You should be able to see this with a straight edge at the cylinder tops.

I would measure the cylinder length with the cylinders off the engine with a set of calipers. If you compare side to side from the piston tops, you can be introducing error from different con rod lengths, piston pin heights, and differences in cyl to case torque. With the cylinders off you can also drop a straight edge across the cylinder registers check the registers again.

-Chris

[VaccaRabite]

Well I had time to work tonight, so I did more testing - just to make sure. I also did some experimenting with the leakdown tester.

1) the directions say not to run the leak down tester above 80 psi - but they don't say that you get a false reading if you run it below 80 psi. I was running it tonight at 70 PSI to be nice to the tool, and could not figure out why all my measurements were 10% higher. But it back at 80PSI and it was golden.

2) The leak down tester was leaking in 2 places. I put in some fresh teflon tape and that was fixed. I was REALLY hoping that was the cause of my leakdown - jsut the tool being out of whack. But, it wasn't.

I checked the valves for bubbles, and they were sealed tight.

The cylinder to head join only bubbled in 1 location - between the cylinders. Everywhere else seemed to be fine.

Tomorrow morning I am going to pull the head and start taking measurements. I really hope I just need to get the head recut a little.

Zach