Spark, Fuel, or other?

[yegg]

How can a piston be in the wrong cylinder? I understand backwards but not the wrong cylinder. Here are the two that came out of the motor. They seem identical with with exception of the numbers above CD30. One has 3080 and the other has 5347.

Is there a way to tell a front vs. rear piston?

Thanks


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[hulkss]

These pistons look the same, many are not. The intake and exhaust valves are different sizes. There are different valve cut-outs on some pistons and maybe differences in the skirts too. The pistons get really close together when both are at the bottom.

 

[yegg]

A call to two different dealers today got the reply that the stock cylinders are in fact the same and not cylinder specific.

At least that is one thing I can take off my check list.


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[yegg]

Spark, Fuel, or other?

Friend came over and help me verify that air is leaking A LOT from both valves in both cylinders.

Very audible air leak from induction module and a decent sound from both exhaust pipes. No bubbles seen in looking down into oil pan through the fill hole.

Tear down is underway again.

So excited to see how I effed up. (Not really)


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[yegg]

Ok. Here is the latest. The bottom line is don’t trust anyone and verify everything yourself.

When I did the original work I was not able to buy just piston rings from the dealer. Instead they sold me a set of rings and pistons from a floor model that went straight to upgrade from the showroom floor. And this is where I screwed up.

Look at 3 o clock and check out that gap. That is what I was sold. Below is my original stock piston.

Yup, a much better fit. I double checked my valves in the cylinder head in a pitch black room with a flashlight in the head and saw absolutely zero light come through the valves.

I also double checked my push rods. The two shorter push rods were properly installed for the intake and the longer push rods for the exhaust.

The above pics are from the front cylinder.

I went ahead and did the leak down test again on the rear cylinder at this point. I did the test with just the cylinder head installed. The rocker arms were already removed. The valves were naturally shut by the spring pressure. I put the piston at top dead center and then did the test. There was zero leakage from the intake or exhaust ports in the head. Instead I heard a lot of air coming through the exposed lifter blocks.

As far as I can tell I am losing compression from the undersized pistons and poorly fitting rings that came with them. I should have looked from the start but this time I did when I removed the rear cylinder and piston. The ring gap for the top compression rings was about 1/4”!

Yeah, I really should have double checked things. I hope new rings on my old pistons solves my problem.

Any and all comments and suggestions are welcome....especially if my logic is flawed! Please don’t let me put it all back together again without mentioning something I should double/triple check.

Thanks


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[hulkss]

Looks like you put 96" pistons in a 103" motor.

Check the valve seal with a thin penetrating fluid like paint thinner in the combustion chambers, not water. Water has a high surface tension and does not work well.

You are lucky it did not start. A piston ring could have broken and got into the crankcase.

Be sure to check the piston ring end gap next time.

 

[yegg]

Latest update is that I got my old pistons, new rings, cylinders and heads back on. I did a leak down test and only have a 7% loss on the front cylinder. The rear head is coming off as I now hear and feel air through the exhaust port. This is really getting old.


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[hulkss]

Getting to know your bike pretty well now I would say.

 

[yegg]

Spark, Fuel, or other?

That’s for sure. Although I’m trying to figure out why I now all of a sudden have an issue at the exhaust valve when I didn’t before. I’m going to retest tonight and hope I was just tired last night. Replacing gaskets like this is getting expensive. I wish I had a way to test the heads/valves without putting them back on.

I read on another forum that 8-12 percent is a good leak down test percentage for a stock motor. Does that seem accurate?


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[hulkss]

Just bolt the head to a flat plate with a used head gasket, then use your leak tester.

Per the HD service manual "Leakage greater than 25 percent indicates that further
diagnosis is warranted."

This is on the bike, not a bench test.

 

[yegg]

So I ran the compression test again and verified I have about 50% leakage. I heard air escaping through my push rod openings as they are not in yet. I am also pretty sure I heard air coming from both cylinder head ports (intake and exhaust).

I am befuddled as to the possibility of air leaking through the crank case. I can get a piece of paper between the piston and the cylinder wall but not past a the top compression ring. Valves I can understand but just not believe at this point.

I have a buddy coming over on Sunday to help out and hopefully his hearing is better than mine. He is bringing his valve spring compression tool and I am just going to relap the valves as soon as he gets here.

On a side note I do believe I pinpointed why my bike has been tough to start at times. One of my ACR solenoids was damn near welded shut. I am going to get 2 on order tomorrow just to be on the safe side.


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[hulkss]

Piston clearance should be much less than a thickness of paper. Piston size is checked 90 degrees to the wrist pin hole below the rings on the piston skirts.

Did you check the piston ring end gaps?

Any air going past the piston rings will come out through the pushrod cover tubes.

 

[yegg]

Spark, Fuel, or other?

Piston ring end gaps are on point. The piece of paper was at the top of the piston at TDC.

Local dealer has a cylinder/piston/ring set that I’m picking up just in case.


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[yegg]

Heard some air (not much) from the push rod tube openings. The cylinder still looks good to me but I’m going to have it measured and I’m going to hone it to get rod of any build up at the top.

Heard and felt air at the exhaust port of the cylinder head. The valve is badly pitted and I guess the lapping done did not do the job. I’m going to ask my boss if he thinks I should cut the valve or just buy a new one. He has the tools to do the valves and seats but the seat is in great shape. See below for a couple pictures of the valve.

Here is the seat.

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[hulkss]

That valve is done. Get a new one.

I would use a flex hone in the cylinder.

 

[yegg]

New after market valve ordered this morning. I wonder what could have caused that one valve to get so beat up.


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[hulkss]

The valve has to sit perfectly on the seat with contact over about an .060 wide band. That is how they are cooled by heat conduction into the head. Once pitting or combustion deposits foul that up, the valve goes bad quickly.

 

[yegg]

Used a flex ball hone on the rear cylinder today.

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[hulkss]

I use a paper towel and Marvel Mystery Oil to wipe the bore clean. It's mostly Stoddard Solvent.

 

[yegg]

New valve hand lapped for minor touch up and installed in the cylinder head. New ACR solenoid installed in cylinder head. Cylinder head installed and showing about 7% loss which is about the same as the front cylinder. I’m calling that done.

Now to finish the rest of the reassembly tomorrow.

Hulkss, I couldn’t have done it without you. Thank you for your guidance.


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