How do my plugs look

My needles are 4HZ21

The only manual I have for my bike is the '82 Seca 400, it list the needle for that motor at 4HZ20. I am guessing mine is probably good for my bike as I think the power nicreased in the motor in '84.

You probably have the wrong needles then judging by the number you have.

 

Well after fixing a few things I beleive I have foundthe problem, left cylinder piston rings. I changed the butterfly seals which were missing pieces and rock hard wit new ones, this got back a lot of color on the plugs to a nice tan color.

The left cylinder is still off a bit but with further checks the compression hot n the left is 20psi lower than the right.

right cylindr 165psi cold - 158psi hot
left cylinder 157psi cold - 128 hot

I squirted a bit of oil in the left and compression wet up to 151psi hot which confirms rings.

I guess this winters project will be pulling the motor out and giving it a refresh of new rings and a general check of everything else in side.

 

I wouldn't jump to that conclusion quite yet. One interesting thing is that your compression goes down with heat, it should go up. One thing that might account for this is if your valve clearance is too tight. As the valves and shims heat up, they will expand, and too small clearance becomes none at all and the valves will hang a bit open.

Despite the potential evidence from the "oil test" I'd first verify that clearance is correct.

My .02 anyway.

Paul

 

These are my numbers for valve clearance,

left exhst 0.007
left intk 0.006

right exhst 0.006
right intk 0.004

So my valves are in spec, is there anything else that might cause lower compression when hot?

I am going to go redo my compression check cold just to be sure, come to think of it I used my old tester for the cold numbers and my new tester for the hot numbers.

 

Now, I'm more guessing... but I'd still say "not rings".

Maybe a bad head gasket, incorrectly torqued head nuts, or a warped head. Maybe, also, a bent valve. If a valve's slightly bent, the part of the valve head that's closer to the seat may hold the valve further open as it expands when hot than it does when cold.

 

But if a valve was stuck open squirting oil in would not seal this and make compression go up, so when my numbers went up doesn't that rule out valves and head gasket since the oil I put in would never reach that high to seal?

 

Ok re-did the cold and hot test with the new tester, my numbers are better.

left cold 141psi hot 149psi
right cold 143pi hot 152psi

I guess my old tester is not working so hot anymore. I doubled check the new tester on my RZ's motor to be sure and and the numbers match what my buddy gave me after a rebuild last month.

Maybe then with the carbs being very dirty and the dry rotted butterfly valv seals it ok now. I am going to buy new plugs tomorrow and go for a nice little drive and check the plugs.

 

Your Compression is good to excellent.
Looks like you need to do the Carbs and leaks.

 

Well, this seems to have come down to a measurement error, so further discussion is purely academic, but...

In my recent engine work, where I did in fact have bent intake valves, the oil still helped. This, along with some derogatory comments someone else I know made about it, makes me wonder how useful the "oil test" really is. I would kind of expect the oil to get get somewhat vaporized in the cylinder and thereby still have an effect on narrow gaps where air would squeeze out if not blocked by a thin film of oil.

For comparison, my worst cylinder, the one with a pretty badly bent intake valve, read 10 psi "dry" and about 50 after adding oil. After replacing the valve (and not doing anything to rings/cylinder/piston), I get about 120 psi there.

Anyway, glad to hear that things checked out well on the retest.

Cheers,
Paul

 

You put Oil in the Hole to determine the likely cause of LOW Compression Numbers.

Low - Dry. Is it Rings or Valves?

Wet - Improvement = Ring related problem
Wet - No Improvement -- Indicates Valves might be involved too.

 

Rick, again, this is experience I'm talking from and again I get the impression you didn't read my post before responding.

My experience: Before work - compression on #3 = 10 PSI. With oil, 50 PSI. Your theory says that means ring problems.

Next step I did was to pull the cams and run compressed air into the spark plug holes. I could hear and smell air coming out of #3 through its carburetor.

Pulled the head and found minor bending on intake valves 1, 2, and 4, and major bending on 3. Replaced all intake valves. Cylinders still showed original crosshatch very nicely and no scoring. Engine only had 6400 miles on it, so I didn't do anything to rings, cylinders, etc.

Put it back together and read 105 PSI cold and dry and 120 PSI warm. This is at somewhat over 6000 feet elevation.

So, while theory would say that a 40PSI improvement in compression by adding the oil indicates a ring problem, my experience says that, in my case, the oil test was, at the least, misleading.

Paul

 

Well, ...
I didn't invent the test.
The Book I go by was written in March, ... back in 1975.

I was pretty sure I had it right.
But, you know me. Check it out.
I checked.

The Ruling on the field stands.
Sustained Low Compression during the Wet Test indicates Rings.

There's a Heading entitled:
Sticking Valves

A Sticking Valve is indicated if a Compression reading fails to:
a) "Climb a little bit with each stroke before indicating peak."
b) "Remains the same during the first several strokes before beginning to climb with visible pressure leaking-down."

Head Gasket

Readings on adjacent cylinders 20 psi lower than the rest indicates Head Gasket failure.

 

Huh?

Before you said:

Wet - Improvement = Ring related problem
Wet - No Improvement -- Indicates Valves might be involved too.

Now you're saying:

Sustained Low Compression during the Wet Test indicates Rings.


Doesn't "Sustained Low Compression" mean, no improvement? Aren't your two statements then contradictory anyway?

Although, that second interpretation does not match what I had been taught. I had always heard the first interpretation. My point on this thread, though, is that, regardless of what the books or old mechanics say, my experiences did not match the "Wet - Improvement = Ring related problem" adage.

I don't make any money either way. Just wanted to let people know what I had found in case it would save some of them from doing unneccesary ring jobs.

Paul

 

Here's what the Book says:

Ordinarily, valves don't all wear-out or burn away uniformly so that uneven compression is generally a sign Valve problems.

However, valves can be differentiated from rings by squirting about a tablespoon of oil into the cylinder, ... cranking the the engine to distribute the oil and then repeating the test. If the Readings show a considerable increase, the rings are at fault. If the Readings remain about the same, the valves are at fault.

 

I'm not arguing with your book. It says what it says. My Clymer manual says that too (of course, it also says that the wear limit on the pistons is .81mm LARGER than the initial bore diameter, and gets the cam installation details very wrong... but those are other stories.)

What I'm telling you is what I found. You keep referring to your book and saying you got it right. Congratulations. However, if I'd followed the advice that you just posted, I'd still have bent valves, and I would have nice new rings, and maybe pistons, that I didn't need. Part of what I dealt with when working on this engine was work done by a previous mechanic who may well have followed that book. He pulled the whole thing apart, swapped in a new head gasket, and apparently didn't notice the bent valves at all.

I would imagine this oil test isn't completely useless. It must work in some, maybe even most, cases, or it wouldn't be so popular. I doubt however, that my situation was the only case in history when it was wrong and misleading.

 

Neither wrong nor misleading.

The Bent Valve would affect how the Compression Gauge read the Hole.

Initially, the test would show some sign of inadequate pressure.
The Hole would lose Compression and there'd be the indication of pressure loss between strokes.

What is it?
Wet it and see, ...
The Gauge would Pump-up more efficiently BUT Still bleed-down slowly indicating a Valve issue.

But like our English Language's Rules of Grammar.
There are Rules.
Exceptions to the Rules.
Exceptions to the Exceptions.

 

Now you've entirely lost me. My gauge doesn't bleed down. Like most compression gauges, it has a check valve to maintain peak readings.

A leak down test, rather than a compression test with a compression gauge, would test for "bleed down." Is that what you're talking about?