Best Head Gasket?

#21
i wasnt saying that the thin gasket wont work just passing the word some ppl may read this and it may help i would imagine if the engine is mildly modded and the pistons in the hole your best off using the .009 i use one on my honda 270 it had plenty of room
 
#24
Why? Don’t you have a compression release?
I do but even so It still sometimes kicked back. My guess was the high timing + compression. My lash is 0.002" cold, 0.004" warm.

Also just because it should have full compression NOW, I'm going back to my base timing. The only reason I bought the 3* key was because I thought it sounded and felt kinda "lazy" and there was no evidence of detonation. Now I know it felt lazy because of a blown head gasket.
 
#26
Forgot one thing, if it is too much compression it will yank the handle out of your hand even if ignition is off. If you can pull the cord ok with ignition off then it is a kickback problem.
 
#27
Should be easy to start if ex lash is set right. Try a snug .001 with piston a few degrees Atdc on compression.
Sometimes I set it to 0.0015" but that's my tightest feeler gauge. I honestly wouldn't feel bad putting it to zero cold because the lash grows so quick as it warms up.
Forgot one thing, if it is too much compression it will yank the handle out of your hand even if ignition is off. If you can pull the cord ok with ignition off then it is a kickback problem.
Interesting point. Might also help to see if it's detonating. Would it be better to test that hot or cold or both?
 
#28
It’s not going to detonate cold. If it only kicks back with ignition on and engine cold it’s timing. If you are running a ultra lite flywheel that could aggravate the issue.
 
#29
It’s not going to detonate cold. If it only kicks back with ignition on and engine cold it’s timing. If you are running a ultra lite flywheel that could aggravate the issue.
I can say it DOES kick back cold with the ignition on if you don't pull the rope with authority. As long as you pull it over fast enough, you're good. That's what led me to thinking timing but we'll see when I get it back together.

I run the PVL cast flywheel. 28* built-in, 3.6lbs.
 
#30
Should not be doing that with 28 degree timing. Try setting ex tight. If you have a compression tester check cranking compression. They vary as reground cams have varying base circles but cr tab is fixed. Should be 80 psi +- 20 lbs
 
#31
It’s not going to detonate cold. If it only kicks back with ignition on and engine cold it’s timing. If you are running a ultra lite flywheel that could aggravate the issue.
Because of the lighter weight of the flywheel creating less momentum, when starting?
I had my engine kicking back pretty bad (broke a recoilstarter and a rope), when I got an ultralight flywheel installed with 32 degree. Now it's set at 28 and problem is almost solved. It didn't kick back with ignition turned off. I do tend to pull start it hard and fast.
Curious to see, if your engine still kicks back.
 
#32
Not sure if this has been mentioned yet but with the ignition turned off, pull the starter slowly until you feel resistance from compression then release the starter (let the rope retract all the way). Switch the ignition on, then give it a brisk pull. If it doesn't start, turn the ignition off and slowly pull the starter until you are on the compression stroke again. Release the starter then switch the ignition on and give it a brisk pull. Repeat this until it fires up. I haven't gotten bit since I started using this technique.

-Ray
 
#33
Because of the lighter weight of the flywheel creating less momentum, when starting?
I had my engine kicking back pretty bad (broke a recoilstarter and a rope), when I got an ultralight flywheel installed with 32 degree. Now it's set at 28 and problem is almost solved. It didn't kick back with ignition turned off. I do tend to pull start it hard and fast.
Curious to see, if your engine still kicks back.
The flywheel I have is much lighter than stock, but it's still not all that light. The "ultralight" flywheels are around 1.5-1.8lbs. My stock flywheel was 5.5lbs.

I've also broken a share of recoils. At least they're cheap as dirt!
 
#34
all the bad boy motors dont use a compression release to pull start a chainsaw they have decompression valve's im thinking about a bad boy gx 390 with a billet cam and flywheel with the built in starter since i have led lights on it already and a harley agm battery
 

65ShelbyClone

Well-Known Member
#35
Standard operating procedure for big single-cylinder bike engines is to bring it up to the top of the compression stroke before giving a healthy kick. The idea is that it both prevents ignition kickback and gets engine inertia up enough to carry through the next compression stroke. I have a high compression Honda XR600 and that's the only way to start it.
 
#36
Standard operating procedure for big single-cylinder bike engines is to bring it up to the top of the compression stroke before giving a healthy kick. The idea is that it both prevents ignition kickback and gets engine inertia up enough to carry through the next compression stroke. I have a high compression Honda XR600 and that's the only way to start it.
What does that do to the spark? Does the CDI know to trigger after TDC as you're kicking it over the first rotation?
 
#39
Okay, update time: It runs!

First I lapped the head. I had already milled the head but it warped very slightly where each of the for head studs clamped it. I did a few tests where I coated the face in Sharpie and gave it a quick hit on the lapping plate to see where my high and low spots remained. The black is low spot and the shiny is high. I got complete contact but this picture is from about halfway through:

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The lapping process:

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These next pictures are pretty terrible because my camera has a mind of its own with the flash. This is the deck surface. It was high across the top and bottom and where it previously blew out just below the oil port was the most pronounced low spot. I probably should have milled it but the setup work scared me into just lapping it for a week straight. Here's the initial test:

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Halfway through:

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And the final:

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Since the side cover gasket kept pushing out, the side cover started to shear the two dowels. Also I gouged the head dowels yanking them out of the block. I machined new dowels, keeping the side cover dowels solid because there isn't any screw going threw them. I made three head dowels because there were three places in the head for them, then I put my head through the wall a few times when I tried to put the head gasket over three dowels.:oops:


I did the compression test a few different ways.

First I set the lash to 0.0015"-0.002" go-no-go on both valves and pulled it with the cord. That gave me 45 PSI.

Then I turned it over with an 800rpm drill. The compression release was still releasing compression: 50 PSI

1600rpm drill. To my surprise, the compression release was still engaged. Not sure if it got stuck or what: 90 PSI

Then I tried setting the exhaust valve lash on top of the compression release (I also indicated the lift of the compression release to be 0.061"). I had to put my big boy 120V drill in low gear and it was extremely violent, stripping out the clutch on occasion. At 400rpm it gave me 175 PSI.


Seeing I get 45 PSI pulling the engine, I already knew it wouldn't kick with the ignition off but I tried it anyway and got the predictable result. It actually didn't kick back even with the ignition on. And yes, I did set it back to 28* timing now. Now that I think about it, it used to kick when it had the old NRR 230 0611 cam and it hasn't since I swapped it for a MOD2.

All in all, it runs healthy now, pulls harder than it did before, but it didn't pick up as much as I expected it to.
 

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