E: Engine Valve Timing

Mikeant

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I have just installed new 105 cams. Found the equal lift points and marked cam pinions and the crankcase adjacent. Crank set at 4deg BTDC. Inserted idler and crank pinion. Rotated crank pinion until a keyway lined up and inserted the key. Rotated engine forward by 360+50 degrees and inserted front camwheel into mesh. Next, checking, I get rear cylinder equal lift point at 7.1deg BTC and the front at 2.9deg BTDC. It seems to be the case that one or other of the cams is not inserted correctly into its wheel. There is 4.2deg error.

So questions.
1) is this timing acceptable?
2) If not, how can it be improved? (combinations of a different keyway on the crank pinion - 1.5 deg - and/or moving a camwheel by a tooth - 7.5 deg )
3) should I be moving a cam relative to its wheel?

This is a 1948 Rapide engine with 8:1 CR pistons
 

BigEd

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I have just installed new 105 cams. Found the equal lift points and marked cam pinions and the crankcase adjacent. Crank set at 4deg BTDC. Inserted idler and crank pinion. Rotated crank pinion until a keyway lined up and inserted the key. Rotated engine forward by 360+50 degrees and inserted front camwheel into mesh. Next, checking, I get rear cylinder equal lift point at 7.1deg BTC and the front at 2.9deg BTDC. It seems to be the case that one or other of the cams is not inserted correctly into its wheel. There is 4.2deg error.

So questions.
1) is this timing acceptable?
2) If not, how can it be improved? (combinations of a different keyway on the crank pinion - 1.5 deg - and/or moving a camwheel by a tooth - 7.5 deg )
3) should I be moving a cam relative to its wheel?

This is a 1948 Rapide engine with 8:1 CR pistons
If the cams were not pressed onto the wheels exactly you will find that that it is not possible to get the timing exactly the same for both camshafts. Usually in cases like this people "spilt the difference" using a different keyway in the half time pinion. e.g. In your case, the 4.2º error would be split so that one cam would be 2.2º early and the other one 2.2º late.
I have done this on my 1948 Rapide and it runs fine. Yours will probably run fine as it is without doing anything. If you have a hydraulic press you could push the wheel of one of the cams and move it to a better position. They were pressed on at the factory using an alignment jig.
 

vibrac

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you should examine the half time pinion there is your salvation as Big Ed says you could find a better keyway match 3 degrees split will be of little matter
 

Mikeant

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So remembering we are aiming at 4deg BTDC and with timings of 7.1 and 2.9 BTDC at present, changing the crank to cam wheels relationship by one keyway should result in a change at the cam wheels of 1.5deg. Which then leads to timings of 5.6 deg on rear and 1.4 deg on front. The 4.2 deg difference between front and rear cylinders is still there.

Or....If the crank is moved 2 keyways the timing will be 4.1 BTDC the on rear and 0.1 ATDC on the front. Now if the front cam pinion is now moved 1 tooth that will result in the front now being 7.4 deg BTDC.

So we started with 7.1 and 2.9 and have ended up with 4.1 and 7.4.

Am I thinking straight here?
 

BigEd

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So remembering we are aiming at 4deg BTDC and with timings of 7.1 and 2.9 BTDC at present, changing the crank to cam wheels relationship by one keyway should result in a change at the cam wheels of 1.5deg. Which then leads to timings of 5.6 deg on rear and 1.4 deg on front. The 4.2 deg difference between front and rear cylinders is still there.

Or....If the crank is moved 2 keyways the timing will be 4.1 BTDC the on rear and 0.1 ATDC on the front. Now if the front cam pinion is now moved 1 tooth that will result in the front now being 7.4 deg BTDC.

So we started with 7.1 and 2.9 and have ended up with 4.1 and 7.4.

Am I thinking straight here?
Probably not. Have another play around by moving the half-time pinion and choosing another keyway.
I don't have it to hand at the moment but does it explain it in Richardson?
 

davidd

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As far as I was aware, there were only two makers of 105 cams: Godet and Robinson. I have degreed both and they were exactly the same timing. This does not guarantee that they were pushed into the wheels correctly, but there is a good likelihood that they were assembled correctly.

If your timing is correct, you should find the intake valve open at 29 degrees at 0.020". This is how Patrick said to time the 105 cams and that is how the bike was run on the dyno.
This might be a good secondary check that you are on the correct track. I found equal lift at 0.1275" on each cam and that was produced when the cam was timed as Patrick had requested.

Best of luck,

David
 

vibrac

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I have pushed a few cams in wheels on the racer never looking at any (or maybe there were no) timing marks and then timed using the 4degree rule because as far as I can see it matters not a jot where the cam is on a symetrical wheel if you are using that method. Having said that the 'keyway' is a nice guide in the early stages so I try and get it somewhere near.
Incidentally on a Comet I always work backwards hold the cam in the equal opening position with a screw and washer in the timing case and work back down the gears finally slipping the half time pinion in the nearest slot when the crank is rotated to 4 degrees.
 

Nigel Spaxman

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As far as I was aware, there were only two makers of 105 cams: Godet and Robinson. I have degreed both and they were exactly the same timing. This does not guarantee that they were pushed into the wheels correctly, but there is a good likelihood that they were assembled correctly.

If your timing is correct, you should find the intake valve open at 29 degrees at 0.020". This is how Patrick said to time the 105 cams and that is how the bike was run on the dyno.
This might be a good secondary check that you are on the correct track. I found equal lift at 0.1275" on each cam and that was produced when the cam was timed as Patrick had requested.

Best of luck,

David
Terry Prince makes 105s. His look a bit different I think the base circle is bigger.
 

davidd

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Nigel,

They are not the same cam. This is the problem with calling a cam "105". The Godet and Robinson cams are identical. The Prince cam is not. The Prince cam has its LSA at 105 while the other cams have LSAs at 109.5 degrees. The Prince cam also has a much higher lift.

The 105 cam is supposed to be timed with max lift at 105, but I found when it was correctly timed it had max lift at 108-111. So, the 105 does not refer to anything on the cam. With Terry's cam at least the 105 refers to something on the cam....the LSA.

Patrick gained 7 bhp on his Rapide with the 105 cam. We lost 4 bhp on the Comet using the same timing as Patrick. It was a lot of work to install the cam and run it on the dyno for such a big loss in power.

David
 
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