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Valve advice needed .....

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Hey, it's me .... O&S, the guy that blew up his motor when the valves hit the piston.

Anyway, i did the solvent test wherein you pour solvent into the port and wait for it to drain through the valves all over your floor. (Head is off the bike and the springs are holding the valves closed).

It's been in there for an hour and hasn't even started to seep through.

Saturday i'm going to take the valves out and take them to work Monday and check them for run out, we have V blocks, lathes, dial indicators, etc. there.

My question is this; if the valves by some miracle are not bent, do i trust them and re-use them, or do i buy new ones and lap them into the seat?

Thanks in advance.

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Hey, it's me .... O&S, the guy that blew up his motor when the valves hit the piston.

Anyway, i did the solvent test wherein you pour solvent into the port and wait for it to drain through the valves all over your floor. (Head is off the bike and the springs are holding the valves closed).

It's been in there for an hour and hasn't even started to seep through.

Saturday i'm going to take the valves out and take them to work Monday and check them for run out, we have V blocks, lathes, dial indicators, etc. there.

My question is this; if the valves by some miracle are not bent, do i trust them and re-use them, or do i buy new ones and lap them into the seat?

Thanks in advance.

Since it passes the solvent test you can be assured they are not bent. If they were bent by as little as .002" the solvent would run right out. Valves are very tough. They take a severe pounding every time the motor runs. There can't be any 'invisible' damage to worry about. I would not spend the time and effort to pull them out just to verify that they really aren't bent.

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can someone explain the details of the "solvent test" to me? How does one perform one accurately? What type of solvent, etc. Thanks

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can someone explain the details of the "solvent test" to me? How does one perform one accurately? What type of solvent, etc. Thanks

Stoddard solvent is the standard (without resorting to dumping gas in the ports)

If the valve(s) stay dry (no solvent leaks through to the combustion chamber) all is well with your valve/seat. Yeah, you just dump some solvent in the port and make sure there is enough to cover the entire valve seat. Obviously the head needs to be not attached to the cylinder for this test. 👍

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.... once with solvent, then looking for something even thinner i used 91% Isopropyl alcohol. After dumping the alcohol out i sprayed every thing down a couple of times with WD40 wiping with a clean rag each time. Alcohol is hygroscopic and i didn't want anything etched or rusted.

Tomorrow i'll get some clay and on Sunday check the clearance and see where everything went wrong.

CDS1, yep thin crack between the exhaust valve pockets. I'm glad the piston stayed together long enough for me to get the engine shut down. It had only been idling in the open garage warming up when it started smoking. I shut it down right away.

Here's a couple of pictures. same as the other thread. In one the arrow in the top of the piston is pointing to the far end of the crack, and in the other it is just above the shadow.

dscf7400.jpg

-AND-

dscf7401.jpg

Enjoy.

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.... once with solvent, then looking for something even thinner i used 91% Isopropyl alcohol. After dumping the alcohol out i sprayed every thing down a couple of times with WD40 wiping with a clean rag each time. Alcohol is hygroscopic and i didn't want anything etched or rusted.

Tomorrow i'll get some clay and on Sunday check the clearance and see where everything went wrong.

CDS1, yep thin crack between the exhaust valve pockets. I'm glad the piston stayed together long enough for me to get the engine shut down. It had only been idling in the open garage warming up when it started smoking. I shut it down right away.

Here's a couple of pictures. same as the other thread. In one the arrow in the top of the piston is pointing to the far end of the crack, and in the other it is just above the shadow.

dscf7400.jpg

-AND-

dscf7401.jpg

Enjoy.

wow so there are cracks in the top of the piston, that might be where the smoke is comming from, oil geting into combuston chamber, and are those pits in the valve pockets in the picture of the top of the piston? man i work on motorcycles for a pay check and another teardown is nerve racking but i might throw the stock piston back in and see whats up if that fixes the problem then u know what it is. best wishes U could resolve this whole thing over the weekend

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Well, yeah, the oil was coming up through the crack and combustion was going down through the crack. thats why the oil is discolored. I know the stock piston and cam will work, they were working before i swapped them out, but that doesn't resolve the issue why the HC piston and 190 cam didn't want to work together. The discoloration in the valve pockets is where the valve was touching the piston. The clay will tell me what the actual clearance is and i can then buy another piston and deepen the pockets to clear the valves. It could be a lot of things happening here, i just have to eliminate them one at a time.

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be interesting 2 see weather it is the piston or cam thats why if u leave the new cam in and put the stock piston back in and it trashes your stock piston, well i guess its the cam, if all goes well with the stocker then i would guess the piston, just a thought. u are a first i think, havent heard any one ealse with this one.

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It could be a lot of things happening here, i just have to eliminate them one at a time.

One more thing to check is to see if the T mark on the flywheel is correct and actually agrees with TDC of the piston.

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Yep, thought of that Jeff, but i don't have a degree wheel any more, think i have a micrometer piston stop still around from the old days of timing two strokes. May just see if i can find a degree wheel somewhere inexpensively. Thought about doing that too CDS1, but if it didn't work, it just might really take out the valves and/or the head. I think i'll start with the clay with this piston first.

Jeff, what do you think about advancing the cam timing by one tooth, and doing the clay thing again for a comparison?

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Yep, thought of that Jeff, but i don't have a degree wheel any more, think i have a micrometer piston stop still around from the old days of timing two strokes. May just see if i can find a degree wheel somewhere inexpensively. Thought about doing that too CDS1, but if it didn't work, it just might really take out the valves and/or the head. I think i'll start with the clay with this piston first.

Jeff, what do you think about advancing the cam timing by one tooth, and doing the clay thing again for a comparison?

I think you should be able to find TDC accurately enough by feeling movement of the piston with your fingertips. It can be checked now while the head is off.

Checking clearance one tooth advanced is an excellent idea 👍

Be sure to check intake valve clearance also.

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Ok, it was too cold this morning to take my grandson to the park so i did the valve thing this morning and will take him this afternoon when it's warmer.

Got some interesting results that i don't know how to interpret.

Used my two stroke timing gadget in the spark plug hole to 'feel' TDC. The marks are close, but my gut feeling is that they are not right on. I will need to use a timing wheel to know for sure.

Anyway i did it twice. Once with the cam as aligned as straight as it will go (like i had it to begin with) which i would have to say is about 30' retarded and got:

Both intakes .064" and equal

Both exhausts .023 and within about .002" of each other.

Then i moved the cam one tooth clockwise. Advancing the cam with the piston in the exact same position

and got:

Both intake .063" and equal

Both exhausts .064" and still within about .002"

Also noticed something different. Watching the exhaust rocker arms while rotating the engine, just as the piston starts it's upward travel on the compression stroke, the cam slightly and briefly starts to open the exhaust valves again. Normally when setting valves, etc. i watch the intake rocker assembly as i am searching for TDC on the compression stroke, and don't oay any attention to the exhaust. But since the problem is with the exhaust valves hitting, well i was paying attention to the exhaust rocker assembly.

Weird.

Ok, should i runt this cam in the advanced position to be safe, or clearance the exhaust pockets of the new piston? I mean, it is obviously advanced when put one tooth clockwise (cam, not timing chain sprocket).

And what about the weird bump at the start of the compression cycle?

Thanks for all your help Jeff.

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The bump at the start of compression is the automatic compression release doing its job. It doesn't do anything once the motor is above idle speed.

While .023" isn't as much clearance as we would like to see it certainly is enough so the valves can't contact the piston. 👍

The only reason you would like to have more is because things can happen at very high RPM like the valves could float a bit which would decrease the clearance.

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