timing marks

[Dan M]

At TDC on the compression stroke, where the Guzzi and every other 4-stroke motor I’ve ever adjusted valves on (a fair heap), all have valves spec’d to be set, both intake and exhaust valves have already been closed for approx. 180 degrees of crank rotation through the compression stroke, and both remain closed for another approx. 180 degrees of crank rotation through the power stroke. That leaves 360 degrees of crank rotation where BOTH intake and exhaust valves are closed. Right smack in the middle of this is TDC on the power stroke. It would seem that there’s something like a full rotation of the crank available for setting valves, when both intake and exhaust valves are fully closed – that is, both on their base circles.

 

 

Both cam lobes are not exactly at the base when the piston is at TDC compression anyway. If they were that would mean both intake and exhaust open at the same time. Right?

TDC (compression stroke) just insures both are off of the ramps. With valve overlap and exhaust scavenging there isn't a full crank rotation before you hit either ramp but it is a pretty good distance.

[Guest ratchethack]

Both cam lobes are not exactly at the base when the piston is at TDC compression anyway. If they were that would mean both intake and exhaust open at the same time. Right?

Dan, I think you missed something. Take another swag at it. At TDC compression, (per my post above) both intake and exhaust valves have been closed for 180 degrees, and will still be closed for another 180 degrees. In other words, at TDC compression, both cams are most certainly on the base circle -- ain't no Q about it.

 

Somebody convince me otherwise, and I'll revise my entire concept of 4-stroke motor operation.

 

Now at TDC on the exhaust stroke (you know, the other TDC), we have valve overlap -- that small number of degrees of crank rotation when the exhaust tappet is coming back on the cam base circle from holding the exhaust valve open and the intake tappet is just ramping off the base circle of its cam to open the valve for the intake stroke -- and indeed both intake and exhaust valves are slightly open at the same time. This is the TDC where you know not to attempt to set the valves -- 'cause not only can't you get feeler gauges under the rockers, but you can't spin the pushrods OR rock the rockers on thier spindles.

[Dan M]

Dan, I think you missed something. Take another swag at it. At TDC compression, (per my post above) both intake and exhaust valves have been closed for 180 degrees, and will still be closed for another 180 degrees. In other words, at TDC compression, both cams are most certainly on the base circle -- no Q about it.

 

Somebody prove me wrong, and I'll revise my entire concept of 4-stroke motor operation.

 

Now at TDC on the exhaust stroke, we have valve overlap, when the exhaust valve is coming back on the cam base circle from holding the exhaust valve open and the intake valve is just ramping off the base circle of its cam to open for the intake stroke.

 

 

I read Greg's post too quickly while drinking. Yes they are both in the meat of the base circle. I interpreted it as center of the base. My Sunday evening posts tend to be a little out of focus.

 

So far as 360 degrees between ramps, I'm not too sure. Certainly cam duration plays a roll and it has to be close at BDC. I don't think I'd set lash near it. That ex valve has to be starting to open by the time the piston starts back up after combustion.

Makes me want to pull a valve cover and see exactly when things happen.

 

Edit: There is overlap at both ends. Valve timing from the V11 manual - Intake opens 22 degrees before TDC / closes 54 degrees after BDC. Exhaust opens 52 degrees before BDC / closes 24 degrees after TDC. That is 254 degrees with the valves closed during compression & power strokes. So you are off by 106 degrees of rotation.

 

Did I convince you otherwise???

[Guest ratchethack]

Edit: There is overlap at both ends. Valve timing from the V11 manual - Intake opens 22 degrees before TDC / closes 54 degrees after BDC. Exhaust opens 52 degrees before BDC / closes 24 degrees after TDC. That is 254 degrees with the valves closed during compression & power strokes. So you are off by 106 degrees of rotation.

 

Did I convince you otherwise???

Dan, beyond the grossly incorrect estimates of crank rotation degrees that I used for illustration, not knowing them or having looked them up, this doesn't conflict with what I've posted. BDC is not important here.

 

What you've noted is the valve overlap at TDC between exhaust and intake strokes. There is no valve overlap, nor are valves open at TDC between compression and power strokes.

 

You DO understand that we have two entirely separate states of operation of the 4-stroke motor at compression TDC vs. exhaust TDC. Yes? In other words, compression TDC separates compression and power strokes. Exhaust TDC separates exhaust and intake strokes.

[Dan M]

Dan, beyond the gross estimates of crank rotation degrees that I used for illustration, not knowing them or having looked them up, this doesn't conflict with what I've posted. BDC is not important here.

 

What you've noted is the valve overlap at TDC between exhaust and intake strokes. There is no valve overlap, nor are valves open at TDC between compression and power strokes.

 

I never said any valves were open TDC compression.

You noted that there is 360 degrees of rotation with the valves closed. There is not. There is 254. The issue we've been talking about is where the crank has to be when adjusting valves. My only point is while the range of crank rotation with both valves closed is wide, it is not 360 degrees wide. There is indeed overlap on all but TDC compression stroke. Both valves are closed from 128 degrees before until 126 degrees after. Beyond that range one or the other is open.

 

And yes Ratch, I fully understand.

[Guest ratchethack]

You noted that there is 360 degrees of rotation with the valves closed. There is not. There is 254. The issue we've been talking about is where the crank has to be when adjusting valves. My only point is while the range of crank rotation with both valves closed is wide, it is not 360 degrees wide. There is indeed overlap on all but TDC compression stroke. Both valves are closed from 128 degrees before until 126 degrees after. Beyond that range one or the other is open.

Dan, per note above, I hadn't looked up the numbers and was using gross estimates on degrees of crank rotation. Of course it was not accurate. I think we're saying the same thing, but you were astute enough to look up the numbers for accuracy.

 

My whole line of reasoning here is to illustrate that with 254 degrees of crank rotation where both intake and exhaust valves are closed (thanks for the correct numbers), in the middle of this (or very very close) is TDC compression, where we know that both intake tappets and their respective valves are on the base circle.

 

So to get back to the original point and re-state it again, we have nearly 254 degrees of crank rotation, (not 360 as I had used for illustration) to set the valves. I reckon this puts the notion of having to set the valves dead nuts accurately at TDC to rest, and finally puts some numbers on just how far off from TDC compression you can be and still get valve adjustment 100% accurate. Hence the Luigi's omission of TDC marks on the flywheel, if and wherever they may've done this. It presents not so much as an inconvenience of any kind for all practical purposes, nor (as has been pointed out) in the event of no marks a-tall, is there any potential confusion possible by re-assembling the flywheel on the crank in any of 6 possible orientations on the mounting studs.

 

Greg had suggested previously that Guzzi may have spec'd valve adjustment at some point OTHER THAN when when both valves and their tappets are on the base circle. I think we've both explored this and have agreed here that this is not possible. Maybe Greg will comment when he sees this. I reckon he's on his way to MI on the mighty Eldo (or one o' his many Guzzi stable alternates) at this very moment.

 

HOLD THE PHONE! Greg's off today. That means he's asleep, and it might be many hours -- or even tomorrow before he logs on.

[Greg Field]

I didn't suggest anything. Rather, I pointed out that assumptions were being made that may or may not be valid.

[Guest ratchethack]

I didn't suggest anything. Rather, I pointed out that assumptions were being made that may or may not be valid.

G'mornin' Greg! Well now I just gotta ask. After the above exploration of this, in which I think at least a few of us (myself included) have learned something more than we knew previously, d'you think those assumptions (that is, that valve clearances are set with tappets on the base circles of the cams) are valid?

 

Enquiring minds. . . (well, you know)

[Greg Field]

Probably. But as I said, until I personally verify it, I'll stick with the factory recommendation. Had some of yers's heads spinning for a second, though. There's some good in that.

[Guest ratchethack]

Had some of yers's heads spinning for a second, though. There's some good in that.

Spinning is the word alright. For awhile there I thought Dan's overlap and me own overlap had improperly overlapped. . . The danger there, o' course, would be that n'er the twain would ever properly overlap. . .

 

I think we finally got on the same page, though.

 

Now this is just me, but next time I'll be even LESS inclined than "not much" to get the ol' donk close to TDC setting the valves.

[Dan M]

Spinning is the word alright. For awhile there I thought Dan's overlap and me own overlap had improperly overlapped. . . The danger there, o' course, would be that n'er the twain would ever properly overlap. . .

 

I think we finally got on the same page, though.

 

True enough. It all started yesterday when I was feeling a little slappy while talkin overlappy but now all are happy.

[Tinus89]

Hey all,

 

Just a brief question regarding this topic: on a V11 engine (Fuel Injected), how do I determine which orientation the phonic wheel should have on the crankshaft? There are two options, which of course give you a 50% chance of sparking on exhaust stroke, which doesn't really make the engine tick over...

I dismantled it and before I could mark it, the pin fell out. 

Is there a way to do this without the use of special tools?

[Tinus89]

Hey all,

 

Just a brief question regarding this topic: on a V11 engine (Fuel Injected), how do I determine which orientation the phonic wheel should have on the crankshaft? There are two options, which of course give you a 50% chance of sparking on exhaust stroke, which doesn't really make the engine tick over...

I dismantled it and before I could mark it, the pin fell out. 

Is there a way to do this without the use of special tools?

 

Anyone?

[LowRyter]

I use the timing marks  (d & S) on the flywheel.  Then I take my feeler gauge, if I can get the gauge in there, the valves are closed and and be adjusted, if I can't get the feeler in there, I know I am 360 out and that one (or both?) of the valves is open.

 

I am not sure this answers your question but I use the marks and feeler for TDC on the compression stroke.

 

I also put a red mark on the spinner of the front of the engine so I can look for the timing mark.  This is because I can easily "overrun" the D/S  on the compression stroke since there is little resistance in the valve  train and no compression with the spark plugs out.  I can't remember if I made the mark for the D or S.

[Chuck]

Ok, I'll take a stab. *I've never done this on the V11* but I'd bring the S cylinder up to TDC ready to fire. I'd install the phonic wheel so it had just gone past the sensor. That's just a SWAG, of course.