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Author Topic: s cams  (Read 5870 times)

ace.cafe

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Re: s cams
« Reply #45 on: February 04, 2014, 02:37:40 PM »
I don't know what timing numbers the S Cams have, but the regular Iron Barrel cams respond quite well to a 1 - tooth retarding of the inlet cam in the Iron Barrel engine applications. If the inlet closing timing of the S Cams is similar to the standard Iron Barrel cams, then I would expect good response to that also.
Extending the inlet closing timing to a later closing angle is a method known to increase the high rpm power, and also will often extend the rpm range higher too. However, there is a limit to this, and a whole tooth is a lot of degrees retarding, so it would need to be verified. Smaller adjustments may be possible with an adjustable timing pinion or offset Woodruff key.
Retarding will have the effect of reduced working compression if you retard it far enough, so that should be taken into consideration when doing that. Since retarding actually presents more clearance from piston to valve at TDC, it may be possible to restore some of that compression by removing a gasket (or even shaving the bottom of the barrel a little) to get the piston a little higher in the bore for more compression.
Anybody thinking about that had better know what he is doing before going down that road. It is a rather advanced sort of modification, which requires understanding what is happening and why.
« Last Edit: February 04, 2014, 07:01:44 PM by ace.cafe »
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boggy

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Re: s cams
« Reply #46 on: February 04, 2014, 04:29:17 PM »
I took it to around 90 mph with no fuss and a bit in reserve, it saw 80 mph in 4th gear with more to come, as well.
 

ahhh... that is awesome.
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Adrian

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Re: s cams
« Reply #47 on: February 04, 2014, 10:03:14 PM »
The oil pump spindle is worth checking, the AVL might survive without oil for a few seconds longer than the original design, but we really don't want to go there.

I really recommend checking the end float of the oil pump gears (both ends, guys!), if they're not spinning freely you'll be able to tell your friends how much a new oil pump spindle (and possibly a full rebuild) costs if you insist on just throwing it all back together.  Some O rings sold for sealing the pump end plates are thinner than stock, which I suspect won't help.

Yep, forgot to check this on the project, took the timing cover off to fit the new magneto (C.I. model crankcases) and noticed a knackered pump spindle after just starting the engine up a few times. The spindle would hardly turn by hand. Hmm... End covers off, it all spins freely... I ended up refacing the pump gears on a sheet of fine wet and dry/WD40 over a handy bit of plate glass (I love hi-tech solutions), all sorted now.  :)

A.

Bill Harris

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Re: s cams
« Reply #48 on: February 04, 2014, 10:26:41 PM »
I retarded the intake 'S' cam one tooth on the Harris Scrambler and got 160 PSI compression on a hot engine, stock AVL head, stock piston, with a 30mm PWK flat-slide carburetor, throttle wide open.  I don't think I lost much, if any compression by doing this.

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Cheers,
Bill

ace.cafe

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Re: s cams
« Reply #49 on: February 04, 2014, 11:21:57 PM »
I retarded the intake 'S' cam one tooth on the Harris Scrambler and got 160 PSI compression on a hot engine, stock AVL head, stock piston, with a 30mm PWK flat-slide carburetor, throttle wide open.  I don't think I lost much, if any compression by doing this.

Royal Enfield people are good people

Cheers,
Bill

Did you happen to have a reading of the compression prior to the change?
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Bill Harris

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Re: s cams
« Reply #50 on: February 05, 2014, 02:01:30 AM »
Did you happen to have a reading of the compression prior to the change?

ace.cafe,

I could not check the compression with the 'S' cams timed to the marks because I had intake valve to piston interference so I don't know what the compression would be.  With the stock AVL cams timed to the marks I got about 155 psi.  I don't think with the intake 'S' cam timed to the mark would make much more compression than what I'm getting with it retarded one gear tooth.  I'm very happy with the 160 psi I'm getting.  I can only speculate on what the compression would be with the 'S' cams timed to the marks.

Do you know what the C.R. is with 160 psi compression in this engine with a stock bore and stroke? 

Cheers,
Bill
« Last Edit: February 12, 2014, 05:35:37 PM by Bill Harris »

ace.cafe

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Re: s cams
« Reply #51 on: February 05, 2014, 12:20:14 PM »
I would need a little more data to be able to say what CR the piston is.

I used my calculator to try to figure out as much as I could.
Assuming that the piston is 8.5:1 like it is often stated to be, then I used that figure in the calculator.
Since I don't know the timing points of the cams, I had to try a bunch of numbers to see what comes up with 155 psi compression at your elevation above sea level.
So, with an assumption of 8.5:1 piston at your elevation, and a cam that closes the intake at the .050" lift point at 37 degrees ABDC, that would give you 155 psi. This would typically be about what we get with the standard Iron Barrel cams which have a seat timing for intake closing at about 60*ABDC. So, we might extrapolate that to say that these AVL cams might have similar intake closing timing as the Iron Barrel, but uses a higher compression piston. Maybe.

To get 160 psi compression test pressure with different cams, I left everything the same, except I moved the intake closing timing. This showed that the cam would have 5 degrees earlier intake closing timing than the stock cams. That would bump the compression some, with all else being the same. That's assuming you didn't change anything like piston height with different base gasket, or different chamber volume from a thinner head gasket, or anything like that.

This is based on some assumptions, because some of the usual necessary data needed to be guessed at, with some reasonable guesses that are likely not too far off.

If you got this AFTER retarding the inlet by a tooth, to avoid piston/valve contact at TDC, I would conclude that the S Cams(as the dots are marked) have quite advanced timing in terms of early opening and closing of the intake valve, and probably a very much tighter lobe center angle, compared to stock AVL cams.
I would also assume that if you had to do this retarding of the intake to avoid piston/valve contact, that everybody needs to do this with the S Cams. Is this the standard installation recommendation for the S Cams? 
« Last Edit: February 05, 2014, 12:33:35 PM by ace.cafe »
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Re: s cams
« Reply #52 on: February 05, 2014, 01:52:39 PM »
Hi all.
In most cases, the 'S' cams work timed to the 'dots', but the two I know of that needed to be retarded on the inlet cam by 1 tooth are the machine owned by Bill Harris and the machine I have here.
 That said, I have been aware of the close proximity of the valves to the piston crown on TDC overlap on these machines since I first got involved with them and always stress that when fitting these cams, the engine should be turned over very gently by hand with the spark plug out, to check for interference between valves and piston.
 My favourite way is to fit the exhaust cam alone to start with and test with the usual 'nil' valve clearance first. If all is well like this, I then unwind the adjuster [to lengthen the pushrod] by 6 flats of the adjuster, or 1 full turn. I repeat the test and if there is no sign of valve / piston interference, it is good to go, although 8 flats and clearance is a bonus, the 6 flats will do. I have not heard of an exhaust cam giving any clearance issues while timed 'on the dots' to date, but if the case were to arise, advancing its' timing would be called for.
 Next, the inlet cam goes in 'on the dots' and again, the engine is turned over very carefully by hand with the valve clearance at 'nil' - a spanner on the worm nut hexagon is good for this. Either, the engine will make two full revolutions, or it may come to a stop as it just comes up on TDC overlap. If all is well, I lengthen the pushrod adjuster by 4 flats and if there is still no obstruction, it is good to go, although 6 flats clearing is a bonus. If I encounter an obstruction, either set at 'nil' clearance, or overadjusted, then I retard the inlet cam by 1 tooth, as I have done in the machine currently here, which has a 64 mm diameter, 2 mm deep 'raised' area in the centre of the piston crown [see below], but the valve faces left standard. On the machine I tuned a few years ago, I bevelled the faces of the valve heads and reduced their diameters very slightly, to give leeway for all the different cams and timings that I tried, so I had a little extra leeway with this machine.
 In view of how well this machine is working [with 9.2:1 compression] with the inlet cam retarded by 1 tooth, perhaps I should recommend this as the default timing and 'on the dots' as the alternative that may not always be workable.
 I will do some digging later, as I wrote up all the cams and cam timings tried in the AVL a few years back and the 'S' cams' data will be in with them. It has also been mentioned that the depth of the cuts on the valve seat faces can vary from the factory, so, some valves may be closer to a piston than others.
 B.W.
« Last Edit: February 05, 2014, 02:02:44 PM by Bullet Whisperer »

ace.cafe

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Re: s cams
« Reply #53 on: February 05, 2014, 02:29:46 PM »
Thank you, Paul!

Just wondering about that piston in the picture. I thought the AVL pistons were flat or dished. What is that piston?
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High On Octane

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Re: s cams
« Reply #54 on: February 05, 2014, 03:39:42 PM »
Thank you, Paul!

Just wondering about that piston in the picture. I thought the AVL pistons were flat or dished. What is that piston?

I was wondering this too.  That piston crown doesn't look familiar.  It almost looks like something out of a diesel tractor.

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tooseevee

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Re: s cams
« Reply #55 on: February 05, 2014, 04:34:56 PM »
I was wondering this too.  That piston crown doesn't look familiar.  It almost looks like something out of a diesel tractor.
Scottie

            I'd also like to ask BW what brand cylinder base & head gaskets he uses. I'm gathering various bits & pieces of information from all over the place on gaskets before my head comes back from the wizards.
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Re: s cams
« Reply #56 on: February 05, 2014, 05:31:15 PM »
Thank you, Paul!

Just wondering about that piston in the picture. I thought the AVL pistons were flat or dished. What is that piston?
Hi Ace,
 That is a stock piston, with a modified crown, to suit the cylinder barrel being shortened by 2 mm, the bottom of the liner must also lose 2 mm, or it will foul on the flywheels. Basically, I machine the piston crown inwards, removing 10 mm radially and to a depth of 2 mm. This has the effect of retaining the squish clearance, while 'adding' a 2 mm deep by 64 mm diameter 'dome' in the centre, to raise the C.R. from 8.5:1 to 9.2:1.
 Any gaskets I use would be supplied by Hitchcocks and are nothing special that I am aware of.
 B.W.

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Re: s cams
« Reply #57 on: February 09, 2014, 03:06:30 PM »
I have just found some of my original notes from the AVL Electra X project from 2008.
 The valve timings I recorded were as follows, for both STD and 'S' type cams timed 'on their marks':
 In Opens   STD =  9 deg BTDC
              S cam = 30 deg BTDC [1 tooth retarded = 12 deg] 
 In Closes   STD = 54 deg ABDC
              S cam = 75 deg ABDC [1 tooth retarded = 93 deg]
 EX Opens  STD = 72 deg BBDC
              S cam = 85 deg BBDC
 EX Closes  STD = 18 deg ATDC
              S cam = 50 deg ATDC
 Despite using some painstaking and accurate measuring methods, I rarely get exactly the same results to the degree twice in a row, particularly with RE Bullets, but the figures shown would stand pretty well for the machine I tuned at the time and the three batches of 'S' cams I have already had made are copies from these very cams which were sent away to the cam makers for this very purpose, so the above should be a good guide.
 Retarding [or advancing] a cam by 1 tooth = 18 deg of crank rotation relative to it, this is allowed for in the above figures in brackets for the inlet 'S' cams.
 It will also be noted that the exhaust valve 'gets away' with being partially open at lift / degree figures which would certainly cause trouble for the inlet valve and piston, if timed likewise, but on the other side of TDC, obviously, and this is because the exhaust valve is so much smaller in head diameter than the inlet valve.
 B.W.
« Last Edit: February 09, 2014, 06:42:11 PM by Bullet Whisperer »

ace.cafe

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Re: s cams
« Reply #58 on: February 09, 2014, 04:28:50 PM »
B.W.,
Great info!
Thanks for sharing that.

I would be happy to comment on my views of what might be expected to happen performance-wise, regarding the different timings of the different installations of these cams, if anyone wants to hear that.
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Re: s cams
« Reply #59 on: February 09, 2014, 04:45:01 PM »

I would be happy to comment on my views of what might be expected to happen performance-wise, regarding the different timings of the different installations of these cams, if anyone wants to hear that.
Please feel free to do so, Ace !
 B.W.