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

[TADracer]

May I ask, how are you measuring your clay thickness accurately?

Reason I ask is that I have never done that method before. I use slotted cam sprockets, the cams must be degreed in when they are removed so a dial indicator (like in the picture) and a degree wheel are needed. Very accurate and part of the routine is checking the piston/valve clearance (with everything tight and torqued to specs.)

Now I do not know about your piston/head setup but my 79SF measures out around .065" on the intake side at the extremes of the cam sprocket adjustment which would be at 107 degree lobe center (101 is stock). So that is 6 degrees advanced putting the intake valve at the worst case scenario for a collision. In the past I have run a .030" copper head gasket with no ill effects so it seems like you should have plenty of room.

BTW, a stock head gasket, crushed, should mic out around .051" on the flame ring.

[3Phase]

May I ask, how are you measuring your clay thickness accurately?

I used a Harbor Freight digital caliper. If you look closely at the pictures of the sliced and diced clay you can barely see the marks where the caliper touched the clay.

Reason I ask is that I have never done that method before. I use slotted cam sprockets, the cams must be degreed in when they are removed so a dial indicator (like in the picture) and a degree wheel are needed. Very accurate and part of the routine is checking the piston/valve clearance (with everything tight and torqued to specs.)

Now I do not know about your piston/head setup but my 79SF measures out around .065" on the intake side at the extremes of the cam sprocket adjustment which would be at 107 degree lobe center (101 is stock). So that is 6 degrees advanced putting the intake valve at the worst case scenario for a collision. In the past I have run a .030" copper head gasket with no ill effects so it seems like you should have plenty of room.

BTW, a stock head gasket, crushed, should mic out around .051" on the flame ring.

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I don't remember the numbers off the top of my head but I haven't changed the stock '79 cam timing at all. I do have a very good dial indicator and degree wheel but I'd have to bolt up a baseplate like you did and pre-measure stuff to get the baseline zero for the measurements. After all of that, it is still possible to make an incorrect assumption, measurement, or a math error but a dented chunk of clay is simple, totally visual and you can go back and look at it as many times as you want until you get bored and remove the clay.

The main disadvantage to using clay is that you can only use it once: two complete revolutions of the crankshaft from TDC and then stop, pull the head and measure the clay. With a dial indicator and degree wheel you can turn the crankshaft and watch the needle move back and forth on the dial until your arm gets tired.

To cut the clay, very carefully slice it in half with a new, lightly greased/oiled razor blade. Do not press down while you're cutting or it'll scratch the piston and/or distort the impressions from the valves and you'll have to start over.

Very carefully measure the deepest parts of the impressions in the clay with a dial or digital caliper. Do not press down or sideways with the caliper, it'll distort the impressions from the valves and you'll have to start over.


I do apologize for not adding the Metric (English) conversion numbers!

First clearance measurements:
Intake 1.4mm (0.055") clearance
Exhaust 1.9mm (0.0748") clearance

Second clearance measurements:
Intake 1.9mm (0.0748") clearance
Exhaust 3.3mm (0.130") clearance

The old, re-used, Yamaha head gasket: ~1.25mm (0.0492") on the gasket and the fire rings.

The (green) D&K base gasket from Cruzin' Image: ~0.49mm (0.191"). That may change after it's gone through a bunch of heat cycles but right now it's so close to its original ~0.5mm (0.0197") dimension that it makes no difference.

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[WMarshy]

Are these OEM pistons?

[3Phase]

Are these OEM pistons?

Yep. The first one was the original #1 piston from my '80G, the second one was the #1 piston that came with the XJ11 10M jugs that I used for both tests.

Think of the two clearance checks as:

#1) Worst Case: no base gasket and both valves are totally tight and out of adjustment.

#2) Good to Go: has a base gasket but one valve is slightly out of adjustment.

Even the Worst Case clearance was probably still ridable. Unfortunately, the '79SF head and valves are no good. I'm pulling the head off of my running-but-smoking '79F engine to see if the head can be used.

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[trbig]

Dan Hodges told me a long time ago when I was checking into this that as long as there was a minimum of .050" clearance, you should be good to go. Looks like a good way to have a cheap boost in compression if you can get the timing to match the cams.

[3Phase]

Tod,

I really hope it works! I read Dan's post a long time ago too (read all of his posts, actually ) and kept it in mind while I was claying the pistons.

I already have the '79F and SF ignition timing parts so I can set it up when I finish goofing around with the top end and cylinders. If I want to go totally crazy I can look around and buy a set of '78E timing parts.

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[WMarshy]

Yep. The first one was the original #1 piston from my '80G, the second one was the #1 piston that came with the XJ11 10M jugs that I used for both tests.

Think of the two clearance checks as:

#1) Worst Case: no base gasket and both valves are totally tight and out of adjustment.

#2) Good to Go: has a base gasket but one valve is slightly out of adjustment.

Even the Worst Case clearance was probably still ridable. Unfortunately, the '79SF head and valves are no good. I'm pulling the head off of my running-but-smoking '79F engine to see if the head can be used.

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That's good to know because if you ever get lazy and the bike needs a valve adjustment you know it shouldn't get so tight that they clash and wreck the upper end.

Revisit some of Dans posts because he seemed certain that better gains would be had by using one 78 cam and one 80 cam, not both from a 78... Just can't recall which, intake or exhaust.

Thanks for going through the pain. Now if we can get the same info for the 1200 BB kit I bought a while back that would be great. They are supposedly designed after the later '80+ piston... Time will tell but from your info I suspect they will work fine.

[ViperRon]

I can say for certain you can run with no cylinder to engine lower gasket. Just use good high temp grey and put the O rings in for the 1198 Japan overbore kit. Bore the cylinders and fine hone till you have a tight .009 ring gap and you are good to go. But you may find that as soon as the rings seat compression jumps to a level where a regular battery can just slowly crank the engine when the engine is hot. I am at 170 compression cold. Starts good runs great.

[WMarshy]

I can say for certain you can run with no cylinder to engine lower gasket. Just use good high temp grey and put the O rings in for the 1198 Japan overbore kit. Bore the cylinders and fine hone till you have a tight .009 ring gap and you are good to go. But you may find that as soon as the rings seat compression jumps to a level where a regular battery can just slowly crank the engine when the engine is hot. I am at 170 compression cold. Starts good runs great.

[TADracer]

Scott, if you have a dial indicator then it should not take more than a few minutes to set up on #1 (or #4) intake. Doesn't need to be a drilled plate like I use, only a good mount somewhere on the motor. You don't need a degree wheel for a decent check the clearances. Rotate the motor so it is a notch before the F mark and then zero your dial. Push down on the bucket and take the reading. Then rotate the motor about 5 degrees, zero and check again. After a check or three your clearances will begin to open up and you can stop checking. Switch to the exhaust and do it again. Then if everything is OK, just leave the head on and start assembling. Plus, you will sleep better at night.

[WMarshy]

I can say for certain you can run with no cylinder to engine lower gasket. Just use good high temp grey and put the O rings in for the 1198 Japan overbore kit. Bore the cylinders and fine hone till you have a tight .009 ring gap and you are good to go. But you may find that as soon as the rings seat compression jumps to a level where a regular battery can just slowly crank the engine when the engine is hot. I am at 170 compression cold. Starts good runs great.

Sorry, dont mean to derail the intent of this thread but, Ron did you notice any performance improvement with the 1198 kit since compression took a hike? Is everything else stock (timing, cams, exhaust, carbs etc)?

[3Phase]

Don't worry about hijacking the thread, that's what threads are for!

Ron, that overbore info is the kind of thing we need to know, thank you!

Mike, I was going to use both for the clearance check -- clay and dial indicator -- but I couldn't find my valve checking springs, I had none suitable on hand and I didn't feel like borrowing a car to go shopping at the local True Value Yamaha supply store. I used just the inner spring for the clearance check but even that's still too much for me to press down the valve bucket by hand because one of my hands is ATFU.

If I do something goofy again hasn't been vetted by the factory pocket protector platoon and proven over time with years of service and millions of miles with the stock engine like:

mix the model/year cams
mix the model/year pistons or go to aftermarket pistons
slot the cam gears
almost anything else you can think of

I'll find some checking springs then use the clay and the degree wheel and dial indicator just so I'll know exactly where my pistons and valves are at all times, who their friends are and who they're playing with or I really won't be able to sleep at night.

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[TADracer]

If I do something goofy again hasn't been vetted by the factory pocket protector platoon and proven over time with years of service and millions of miles with the stock engine like:

mix the model/year cams
mix the model/year pistons or go to aftermarket pistons
slot the cam gears
almost anything else you can think of

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LOL....But mixing and matching, modifying, changing, grinding, snipping, cutting, polishing and all else that goes along with it is the fun part!

BTW, I don't use checking springs as I hate to pull the head for all this. I ground a common screwdriver as a lever to apply the pressure on the valve from the underside of the camshaft.....reference to the grinding, snipping and cutting parts above.

[ViperRon]

On the 1198 overbore kit. Everything else on the bike is stock cams valves head etc. It did give a performance increase but not like night and day just more low end torque and more high end power. if more info is needed let me know.

[3Phase]

Stainless Steel Valve Checking Springs

I had an epiphany yesterday while I was digging up and repairing a few leaking lawn sprinklers in the front yard.

Toro six inch stainless steel lawn sprinkler springs work perfectly for valve checking springs and will make setting up the valve train a lot easier for me!



XS1100_Valve_Check_Springs_Toro_Lawn_Sprinkler by Scott_Ci, on Flickr

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