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R26 Valve adjustment issue

Mitro007
Posts: 6
Joined: Wed Aug 05, 2020 1:52 pm

R26 Valve adjustment issue

Post by Mitro007 »

I am having problems adjusting my valves on my R26 single cylinder.

Per manual:
I adjust the valves at TDC (OT) of the compression stroke. TDC (OT) at 2 & 1.5 mm. The motor back fires through the carburetor and is difficult to keep running.

When I adjust the valves at TDC (OT) of the exhaust/intake stroke. TDC (OT) at 2 & 1.5 mm. And the motor starts and runs, but there is excessive noise from the valve rockers. When I check my valve clearances at TDC (OT) of the compression stroke, the clearances is vary loose. What am I missing?

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palica
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Location: Montreal, Qc, Canada

Re: R26 Valve adjustment issue

Post by palica »

If you really adjusted the valve at 2 and 1.5 mm, this is the problem. It should be 0.2 and 0.15 mm.
1967 R50/2 with Duna sidecar
1974 R90S

Mitro007
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Joined: Wed Aug 05, 2020 1:52 pm

Re: R26 Valve adjustment issue

Post by Mitro007 »

Thank you for taking the time to respond. It appears that I put the decimal point in the wrong place in my posting. You are correct. It was .2 & .15 mm intake.

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schrader7032
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Re: R26 Valve adjustment issue

Post by schrader7032 »

Are you sure you were on the compression stroke? I usually watch the valve action when I rotate the rear tire with the tranny in 4th gear. Or you could remove the spark plug and use your thumb to feel the increasing compression, and then slowly rotate the engine to bring the next OT into the window.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

Mitro007
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Joined: Wed Aug 05, 2020 1:52 pm

Re: R26 Valve adjustment issue

Post by Mitro007 »

Thanks for your response Schrader, I have spark plug out. Rotating crank at front of engine. Using exhaust / intake rocker positions to determine TDC 1 & watch for next TDC for end of compression stroke. Plastic soft drink straw in the spark plug hole notes as piston has risen.

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schrader7032
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Re: R26 Valve adjustment issue

Post by schrader7032 »

So, you go through the steps to find TDC on the compression stroke, and you set the clearances at 0.2 and 0.15mm. Do you rotate the engine around one more time to confirm the settings?

Then when you get on the road you hear what you think is excessive valve clearances. When you go back to check your clearances are they still at 0.2/0.15mm or have they changed? If they are still the same, then the noise is coming from somewhere else. If they have changed, maybe the lifters are collapsing. Maybe your rocker bearings are failing.

I think it would be good to know if the valve clearances are remaining where you set them or no.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

Mitro007
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Re: R26 Valve adjustment issue

Post by Mitro007 »

In compression the rockers are adjusted .2 & .15. Rotate engine 1 rev to TDC and now the rockers are tight.

When adjusted to TDC exhaust/intake and the rockers are adjusted .2 & .15. Rotate engine 1 rev to TDC and now the rockers are loose as goose.

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schrader7032
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Re: R26 Valve adjustment issue

Post by schrader7032 »

Mitro007 wrote:
Thu Aug 06, 2020 8:54 pm
In compression the rockers are adjusted .2 & .15. Rotate engine 1 rev to TDC and now the rockers are tight.
OK, that makes sense. To digress, on my R69S, if I put the left side on TDC for the compression stroke and set the valve clearances followed by rotating the engine 360 degrees, the left side valves are now tight. But the right side valves are ready to set the clearances on. But for a single cylinder, I think it makes sense that once you set the clearances on the compression stroke, rotating the engine 360 degrees put the cylinder at TDC on the exhaust stroke...valves should be tight. Go another 360 degrees and the valves should be back to loose again, or rather set to 0.2/0.15mm.
When adjusted to TDC exhaust/intake and the rockers are adjusted .2 & .15. Rotate engine 1 rev to TDC and now the rockers are loose as goose.
I'm not totally clear on what you're saying, but I you do the first part, set valves to 0.2/0.15mm at TDC on compression stroke and rotate the engine 360 degrees, you should NOT reset the clearances. As I explained above, the first 360 degrees puts the valve at TDC for the exhaust stroke. Changing the clearances at this point is not correct.

Remember, the engine has four stages of rotation. 1) piston goes down to bottom dead center (BDC). 2) piston rises to TDC to the end of the compression stroke. 3) piston goes to BDC under the power stroke. 4) piston returns to TDC for the exhaust stroke. 1) to 2) results in a 360 degree rotation of the engine. 3) to 4) results in another 360 degree rotation of the engine.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

Mitro007
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Re: R26 Valve adjustment issue

Post by Mitro007 »

The bike has been difficult to start lately. I have set the points at .4mm. Static adjusted for the points to open at the S mark. When motor is running I have used a timing light to set points at S mark at roughly 500 RPM. Spark plug gap is .6 mm.

When I adjust the valves at TDC (OT) of the compression stroke. TDC (OT) at .2 mm for exhaust and .15 intake. The motor back fires through the carburetor and is difficult to keep running.

When I adjust the valves at TDC (OT) of the exhaust/intake stroke. TDC (OT) at .2 & .15 mm. And the motor starts and runs, but there is excessive noise from the valve rockers. I check my valve clearances at TDC (OT) of the compression stroke, the rockers are vary loose.

I am starting the motor with the valve covers off. But even with the covers on it is loader then usual. I am going back out to the garage to double check all the dimensions.

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schrader7032
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Re: R26 Valve adjustment issue

Post by schrader7032 »

I don't understand the reason for setting the valve clearances with the engine at TDC on the exhaust stroke. If you do that, you will indeed have way too much clearance when you're back at the compression stroke. I would not do that anymore...set the clearances the standard way.

I don't know what the RPM should be for the S-mark in the window. More critical would be the F-mark in the window at say 3000 RPM...I really don't know what the RPM should be for a single cylinder, but 3000 or so is about right for a twin cylinder bike. Once the F-mark comes into the window, it should never go past the window.

Sounds like the spark plug gap is about right although 0.6mm is a bit tight...0.7mm is more standard. The points gap of 0.4mm is also a starting point. That number can change a little bit in order to get the S-mark in the window when points open. As I said, the F-mark in the window at full advance is more important.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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