Valve to piston clearance: 2H7 head with 3H5 piston

[3Phase]

As always, click the image to see a larger size picture.


Valve to piston clearance check with green clay: before the clearance check.

The clay is greased on both sides so it won't stick to the piston or valves.

Late-model 1980 to 1982 XS1100/XJ1100 3H5 domed piston.
Early-model 1978 to 1979 XS1100 2H7 cylinder head with small combustion chamber and valves.




Valve to piston clearance check with green clay: after the clearance check.

Intake 1.4 mm clearance
Exhaust 1.9 mm clearance




I'm going to set it up and check it again tomorrow to make sure the clearance numbers are repeatable but I'm happy with the numbers for tonight (this morning). .

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[3Phase]

Something didn't seem right while I was measuring the piston to valve clearances last night and they seemed a little close.

They are.

It was coming up on midnight and I forgot to use a base gasket between the cylinders and engine case so I'll use one when I recheck the clearances again this morning.

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[natemoen]

So this current set of numbers is without a base gasket? So the clearance is smaller?

Lots of us don't use base gaskets, still good numbers to know.

[BA80]

Valve to piston clearance check with green clay: after the clearance check.

Intake 1.4 mm clearance
Exhaust 1.9 mm clearance

Rule of thumb in the automotive world is .100" or 2.54mm. It'll be close but with gaskets in place it should be good to go.

[motoman]

Rule of thumb in the automotive world is .100" or 2.54mm. It'll be close but with gaskets in place it should be good to go.

+1!........Since the stock rods ARE high performance oriented being shot-peened, doubt they'll see any 'stretch' at the 8+K rpm range either.

Good to see you've finially gotten around to solving that mystery Scott. It has been aked about here several times this past winter while U were MIA/hibernation mode........

[Courtney]

So how thick is the base gasket? Don't forget it will compress also as will the head gasket.

[MPittma100]

Clearance

+1!........Since the stock rods ARE high performance oriented being shot-peened, doubt they'll see any 'stretch' at the 8+K rpm range either.

Good to see you've finially gotten around to solving that mystery Scott. It has been aked about here several times this past winter while U were MIA/hibernation mode........

Another factor that is used to establish piston to valve clearance is valve float. OHC engines like these in the XS11 (non-pushrod) do not normally reach a high enough RPM to float the valves.

Some race engine builders run as little as .005" clearance - which they call "none". The normal safe minimum is .090" Exhaust and .100" Intake.

I agree with Gregg that using the base gasket will create plenty of clearance. I may be more concerned with what the new compression ratio is going to be?

Mike

[BA80]

A rough estimated guess of the thickness of the gasket compressed would be .020 - .030 which would put total clearance at approximately .080 - .090.

As Mike mentioned rod stretch and valve float is virtually non existent in these engines. I would go so far as to say that it'll probably be ok even if a base gasket wasn't used.

The compression pressure numbers won't be affected as much as the ratio of combustion chamber volume that will create a stronger explosion and slightly more power.

[D0wn5h1ft]

Curious, what is valve float? Also, how do you get away with not using a base gasket????

[BA80]

Valve float.......for the lack of a more descriptive definition...wiki

The base gasket is basically just a gasket to keep unpressurized oil from leaking, like the valve cover gasket or the oil pan gasket. There are large orange o rings that go around the base of each cylinder that do most of that sealing so just a layer of Yamabond or Threebond will work just as well there instead of the bulky gasket. Without that gasket it will raise the piston crown to deck height. The piston will sit that much higher in the cylinder decreasing combustion chamber volume therefore raising compression slightly.

[D0wn5h1ft]

Valve float.......for the lack of a more descriptive definition...wiki

The base gasket is basically just a gasket to keep unpressurized oil from leaking, like the valve cover gasket or the oil pan gasket. There are large orange o rings that go around the base of each cylinder that do most of that sealing so just a layer of Yamabond or Threebond will work just as well there instead of the bulky gasket. Without that gasket it will raise the piston crown to deck height. The piston will sit that much higher in the cylinder decreasing combustion chamber volume therefore raising compression slightly.

Is it worth cutting out my base gasket?

[BA80]

If you don't need to take off the cylinders for a repair and they aren't leaking at the base, no.

If it ain't broke, don't fix it. It really won't make that much difference.

[D0wn5h1ft]

If you don't need to take off the cylinders for a repair and they aren't leaking at the base, no.

If it ain't broke, don't fix it. It really won't make that much difference.

That's what I was thinking. I'm not taking my jugs off for no reason...

Read up on valve float too. Not good. Good thing it's nothing I have to worry about...except for when I finally send in my cams to megacycle

[BA80]

Actually valve float isn't even an issue with this overhead cam system. Pushrod engines are prone to it because of the added valve train weight because of , lifters, pushrods, and rocker arms. The 11 engine has none of that.

[3Phase]

The old Yamaha head gasket was used for both tests and it's ~1.25mm on the gasket and the fire rings.

The new (green) D&K base gasket from Cruzin' Image was ~ 0.5mm before it was installed. It's glued to the engine block now so I can't measure it without removing it and possibly wrecking the gasket but I'll try to think of something.

The new, unused, D&K head gasket from Cruzin' Image is ~1.3mm on the gasket and 1.6mm on the fire rings. It's asbestos-free, doesn't have any graphite on it at all and it doesn't seem as well made as the Yamaha head gasket. I may have to order a head gasket from Yamaha if the D&K gasket isn't up to snuff.


The cylinder to engine case base gasket was installed for this second test and some fresh clay was put on the piston.



The Intake and Exhaust valve clearance adjustment shims were reset for this second valve to piston clearance check. The Exhaust was only at 8mm and the Intake was only 1mm. The 'old' Intake shim was a 260 and the 'new' shim is a 250. I think the too large Intake shim was the one I gleeped and swapped for Columbo's last valve adjustment and I forgot to check it before I did the clearance test yesterday. Oops....

The Exhaust is now set to 10mm clearance but the Intake is only set to 5mm because I didn't have a smaller shim for the test.



Intake 1.9mm clearance
Exhaust 3.3mm clearance

The Intake valve would probably gain at least another half to a full millimeter of piston clearance if a smaller shim was available to set its clearance to 8mm instead of 5mm.




I'm beat and this thing fought me for most of the day!

Most of the time was lost because the cam timing dots refused to line up correctly. The valves had to be re-shimmed before I could do the test and I couldn't rotate the engine/cams to make sure the shims were seated without messing up the clay so I had to pull the cams back out.

I flat out lost two shims while setting the valves and I still don't know where they are besides, "In the garage!" I need a beer!
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