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E: Engine Valve Timing


SteveO

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Hi all. I'm back with another puzzler. I'm trying to replace the timing gear in my (very non-standard) Rapide. I've got a copy of the service notes, read them. I've also got Richardson and Stevens, but they aren't helping. You see the only timing marks I have, blobs of yellowing paint, when they are lined up make no sense. I'm looking at Fig. 56 on page 107 of Richardson's book, but my gear is completely back-to-front. At TDC on No 1 (rear) cylinder, my keyway on the mainshaft is at 5 o'clock, not 7 o'clock. The slots in the cam pinions instead of pointing to 11 o'clock (rear) and 6 o'clock (front) are transposed. My half-time pinion has a chipped tooth, which we surmise may have occurred when the tooth was centre popped to mark it, as there appears to be a round indent below the damage. One of the slots has a mark, but this is not the slot the key was in and if I put the pinion on the mainshaft, the broken tooth is nowhere near the paint mark on the idler. I'll try and post some pictures shortly, when they have uploaded from my phone.
 

timetraveller

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It is generally a waste of time, with an engine you do not know the history of, to try to use timing marks. The cams might not be standard or have been pushed into the pinions at any position. The correct way to do it is to use a dial gauge and degree plate and plot a graph of valve lift against engine rotation. That way you will find out what the cam profiles are and can then consider how best to time it. Do it for the whole cam profile in case you have a faulty base circle or whatever. If you lack the time or facilities to do that then arranging it so that there is equal lift on inlet and exhaust cams at about four degrees before top dead centre. This will get the bike running. If you do not have access to a dial gauge or degree plate then you need to find someone who has the time and patience to help.
 

vibrac

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I only ever use the 4 degree btdc method and two digital indicators I find that a better method than trying to detect what is the start or end of lift. the only other thing I use is a removable key in the HT pinion so I can try to get as near to 4 degrees on both pots (an impossible task)
 

Robert Watson

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I'm with Vibrac, I have done the 4 deg BTDC on engines with Mk1's, Mk2's, some unknown ones, and prewar 5X ones as well as a set of 105's. they have all run very well except the 105's, as that was only done a few weeks ago and is some time away from starting so the jury is still out!
 

ClassicBiker

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Steve,
I did my cams (MK III)at 4* BTDC and it worked a treat. I've included some links below where Vibrac educated me on doing it and where in appears in Tuning for Speed. One of the links show a simple tool I made for turning the cam against spring pressure. I had the added advantage that I was installing new cams and pinions and large idler and didn't need to replace the half time pinion. So I was able to get all the timing marks to align and didn't need to make any new ones on any of the gears.
So as far as I'm concerned the 4*BTDC is the method of choice. It's simple, expedient, and effective.


 

davidd

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Steve,

It depends a little on what you are trying to do and what tools you have. If you do not have digital dial indicators, then the 4 degree method is a little difficult to do. If you're trying to install timing gears and you want the marks to work like the Richardson figure shows them, then that is a little different. Although, it is important to understand that the Richardson figure shows the timing gear stopped at 4 degrees before tdc.

It would be good to know exactly what gears you want to replace and what cams you are using.

David
 

Glenliman

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It might seem obvious, but I'll post it anyway.
It's a good idea to make your own set of marks once things are set, whether using the 4 degree method or the opening and closing method.
It was sure nice to have the marks there for easy reassembly after pulling my new engine apart for crank balancing.


Glen
 

vibrac

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Steve,

It depends a little on what you are trying to do and what tools you have. If you do not have digital dial indicators, then the 4 degree method is a little difficult to do. If you're trying to install timing gears and you want the marks to work like the Richardson figure shows them, then that is a little different. Although, it is important to understand that the Richardson figure shows the timing gear stopped at 4 degrees before tdc.

It would be good to know exactly what gears you want to replace and what cams you are using.

David
I have used the 4 degree method with a digital height guage first I set the measuring height of the closed valve to be the same by adding washers and shims to the shorter valve with placticene on top of valve cap once they are the same it's a question of measuring down the side of the spring as the valve opens or closes not ideal but doable especially on a comet when you can set the point first, lock cam and work backwards to the HT pinion.
 

Bill Thomas

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I am sure you know that if you turn the engine over, It's many turns before the marks line up again.
I do it by eye, Leave the adjusters out and just watch the pushrods tops as you turn the cam wheel back and forth by hand, I use a straight edge/ruler pointing from the middle of the spindle to between the pushrod tubes, With the slot in the camshaft end upwards on the back pot, With the idler gear not fitted.
 

roy the mechanic

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The 4 degrees method works well, if you can remove the valve caps. Last week I retimed a twin with the motor in the bike. I measured the position of the inlet rocker at tdc, then turned the motor to tdc at the overlap point, measured again, ended up with .107 lift rear, .111 front. It starts third kick cold, first kick hot The owner collected it sunday, returned 3hours later, "it goes really good, was cruising at 70 mph, next time i looked was going 90". I figure there is always more than one way to skin a cat. Provided the inlet is opened more than the exhaust at tdc you will have a reasonable runner.
 

Glenliman

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Re the marks not lining up for many turns. This doesn't matter if you are putting things back together.
Just put the engine in the correct position with a degree wheel then slide the gears together with the marks lined up, same as any other engine.
It worked for me.
The instructions with the MK5 cams were to use the 4 degree method as those cams are difficult to time from opening and closing values.
It worked well and was easy enough to do.

Glen
 
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SteveO

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Thanks for all the suggestions guys. I have a degree disk on the motor ATM, but I don't have any dial gauges, but it appears from Bill Thomas that you can do it by eye. I can see that this sets the valve timing on the back pot, you can then put the half time pinion in the correct place relative to the cams. But how do you do the front pot? I can see you could do the same thing again, but what is the relation to the back pot? Is the next TDC on the front if you turn on from TDC on the back pot on the exhaust stroke similarly an exhaust or do you need to go 410 degrees, i.e. a full turn plus the 50 degree difference between the pots.
 

SteveO

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I don't know what cams I've got in, there is a quite crude 2 marked on the front of one camwheel. Judging from the rest of the engine, everything needle rollers in the timing gear, Gold Star type valves and 32mm inlets gas flowed, they could easily be Lightning or some aftermarket thing.
 

Bill Thomas

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Steve, You said you had the Richardson book.
TDC Or 4 degrees on the back pot, On the wrong stroke !, Both valves open rocking on over lap,
Straight edge pointing in the middle of pushrod tubes and in the slot in the cam facing upwards,
The photo in the book shows at the same time the slot on the front cam pointing straight down !!,
So straight edge from spindle centre straight down,
Then pop the big idler in,
Leave both sets of pushrod adjusters out,
And with the Degree disc on turn the crank and check the settings,
Watching the top of the pushrods for opening, Forget closing for now, Better if someone can help,
You can see by eye if the settings are close.
We did one sometime ago and I was saying it's not far out !!, Nearly there !!, And Ron said
It's more like Mk2 settings !!, Which worked out good !.
And for the first time in my life it worked out the dots were in the right place !!.
Check the degree disc setting by doing it say 10 degrees either side of TDC with one of those things you put in the plug hole ?. Good Luck, Bill.
 

Glenliman

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Thanks for all the suggestions guys. I have a degree disk on the motor ATM, but I don't have any dial gauges, but it appears from Bill Thomas that you can do it by eye. I can see that this sets the valve timing on the back pot, you can then put the half time pinion in the correct place relative to the cams. But how do you do the front pot? I can see you could do the same thing again, but what is the relation to the back pot? Is the next TDC on the front if you turn on from TDC on the back pot on the exhaust stroke similarly an exhaust or do you need to go 410 degrees, i.e. a full turn plus the 50 degree difference between the pots.
Mike Hawthorne sells nice mounted digital dial indicators made to thread into the Vincent heads. They aren't cheap, but well worth having.
One could also make a set if you have a lathe.
Another option- An old ugly set of valve caps could probably be used to mount the indicators. Seems I read in mph of someone doing that.
I borrowed a very nice shop made set of mounted indicators from Dan Smith.
Without the dial indicators it would be pretty tough to know exactly what is happening with the valve timing.

Many decades ago I assembled a Matchless G80 from parts. Somehow I managed to get the valve timing wrong by one tooth. It started easily and ran but sounded like WW3. I was 13 years old ( my excuse) but knew something was wrong and eventually figured it out.
I guess valve timing on some engines can be off a fair bit and the engine will still run. It just won't work like it should.


Glen
 
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Robert Watson

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20180217_153048_HDR.jpg

Back pot is No1 - You set that first as close as you can with the 1/2 time (crank) pinion, then either roll it back to TDC on the front (310 deg) or roll if forward to the same place (410 deg) and set the front one as close as you can, You can then use the various keyways in the 1/2 time to split the difference (if any).
Looking for 4 deg BTDC as being ideal, look for a spread of a degree or two either side.
These are pretty forgiving big old hemi heads and 99.9% on a street bike so a degree or two will be good to go!
 

Gary Gittleson

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VOC Member
All of the above points are well taken but I'd like to add an observation. By coincidence, I have bin fiddling with my timing side to solve some oil leaks and noticed that Mr. Richardson's diagram (the same as the one in the rider's handbook) illustrates the the rear cylinder at TDC but what is not mentioned is that with the cams in those positions, assuming they were never pushed out of the gears and reinstalled, the rear cylinder is on the top of the exhaust stroke and the front is 50 degrees from the top of the compression stroke.

It seems to be a natural assumption that the diagram would show TDC on compression at the rear, but it doesn't.

One more point. Paul Richardson does mention that the position of the keyway on the crankshaft is not significant and can differ from bike to bike. My bike conforms to the Richardson diagram but like Steve's had the crank keyway at 5 O'clock.

My suggestion would be to set the bike up that way as a starting point and then check with dial indicators. I think Steve merely needs to flip the cams 180 degrees and re-check.

I had gone through all of this a couple of years ago, in order to deal with gear backlash and pinion end float. I got a new steel idler and naturally had to replace the half-time pinion which necessitated the use of dial indicators to find the best keyway for valve timing. I then marked the pinion but found that the original marks worked very well. In this new job of fixing the oil leaks, I accidentally pulled the front cam off its pinion and had to recheck the time to get it back in the right place.

Gary
 

oexing

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VOC Member
My approach recently was to find a procedure without messing around with timing marks, opening or closing figures of doubtful files of doubtful cams. So I got extra weak temporary valve springs that I use on all kinds of engines as well to find centre overlap at same lift both valves. For that purpose old valve covers were fitted with 8mm shank clock adapters. I had Sony encoders and a spare DRO for comfortable readings of equal lifts - on one pot, the rear only, first. So no gears on crank or idler fitted first. By hand turning the cam with soft springs I got the equal lift position and marked one suitable tooth on its gear plus a chisel mark on the engine case. So easy to get valve overlap anytime at this spot !
Next was front pot, encoders put on there and cam turned for same equal lift, tooth marked and chisel mark on case - overlap front cam this spot anytime, no guesswork any more with this set of cams and gears.
Next get timing disc on the crank end, find TDC by using a gutted spark plug for hard stop on piston by turning crank one way to stop piston on plug end, disc on zero - turn crank opposite way to stop, read degrees here. TDC is half way between both positions, so set disc to zero at this middle position.
Now for putting on all gears set crank at 4 degrees before TDC for rear pot. In goes the idler and rear cam set to chisel mark and its marked tooth.
Now get the half time gear of the crank and try to find one of the five slots that lines up with the slot in the crank end without turning the crank from its 4 degree position. Once that is done, gear on the crank, you can turn the crank one revolution plus 50 degrees minus 4 degrees for the front cam and its overlap. In this position you should be set to shove the front cam on its shaft unless its gear was not pressed up in a good position on the cam. The marked tooth is meant to line up with your chisel mark for the front overlap on the case.
I was lucky to have new original Andrews Mk 2 cams and gears I got 30 years ago, all perfect.
After all gears are marked with their chisel marks and half time gear installed you can take off heads and mount the original valve springs for good and finish the engine.
The 10mm alu pushrods can be a positive mod, heat extension fits better with all alu engine and look stiffer than the knitting needle originals. But the lineup with the follower cups was not correct as standard so I had 1 mm offset sealing cups with slim o-ring glued in the case for more clearance of pushrods in there. Pushrod shrouds shortened to max bottom length less than big recess in case for this mod to be able to assemble with offset.

Vic
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SteveO

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Bill, yes the penny has dropped, I'm on the wrong stroke. However I have also seen that my timing marks work perfectly for the FRONT pot! When I turn the engine over, lo and behold the slots on the timing gears on the rear pot line where you'd expect. The keyway in the crank is still out though, but that doesn't seem to matter. Is timing the engine on the front pot absolute heresy? If so, I at least have the old painted marks as a starting point. I've finally got the photos to illustrate my dilemma. The first picture shows what I have, the second shows what I SHOULD have and the last shows my knackered old half time pinion. This is a bit of a pain, as it has a keyway punched, but that wasn't the one in use! None of the teeth are marked, and the broken one, which I surmised might be the marked one, doesn't line up with anything. I can only add that I wish I was working on an engine as nice as Vic's or Robert's! I'll have to make my own marks; I've answered my own question by turning the engine over, the two pots are on alternate strokes, which makes life easier.
 

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Normski

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I did mine the same way as Vic, with the exception that instead of using weak valve springs I just removed the tappet adjusting screws and pushrods and used a length of 6mm/1/4” bar,with one end rounded to fit in the follower, this rod was about 20mm longer than a pushrod. With this inserted in place of the pushrod and sticking out through the hole in the rocker where the adjuster screw fits it was easy to make brackets from the head studs to hold the dti gauge to read off this.
 

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