Another camshaft question

[Jentwistle3]

Hi Gang!
Have have some additional camshaft questions, if someone has the time....
I've measured the opening, closing, and lift and obtained the following:
Exhaust-
Opens 79 BBDC
Closes 2 ATDC
Lift (on the lobe) .356
MOP 128.5
Intake-
Opens 35 BTDC
Closes 72 ABDC
Lift (on the lobe) .354
MOP 108.5

Am I correct in drawing the following conclusions:
1) These cam are not a stock B cams
2) The exhaust cam is advanced 18.5 degrees
3) The intake cam is advanced 1.5 degrees
4) The duration of the intake is 287 degrees, 19 degrees more than stock.
5) The duration of the exhaust cam is 261 degrees, 7 less than stock

Is the lift measured on the lobe or on the tappet, ie should the lift include the adjustment gap between the lobe and the tappet?
Where should these cams be timed? Should the MOP be the same as that listed for the B cams?


Thanks in advance
John

[john.p.clegg]

John
Welcome to the black art of camshafts,you seem to have got it all correct...

There are two lift measurements,as you noted,one is the lift of the camshaft,the other the valve lift ( camshaft lift less clearance )

As for MOPs,you are best using the Lotus figures of 110 unless you have data on the specific cams as one can ( if one knows what one is doing ) advance or retard the inlet and/or the exhaust to change the " tune" of the motor.

Good Luck

John

[rgh0]

Hi John

What was the base circle of the cams.
Is the timing you measured lift above base circle on the cam or timing of valve with clearance seat to seat?

As I understand it :
B cam ( std) is 248 degrees valve seat to seat with 0.350 cam lift ( not valve lift)
C cam ( S/E) is 264 degrees valve seat to seat with 0.350 cam lift
D cam ( Sprint) is 272 degrees valve seat to seat with 0.360 cam lift

So exhaust could be a C cam and inlet a regrind for longer duration
setting of timing you found wrong no matter what the cams !

cheers
Rohan

[twincamman]

thank you thank you John ?..ed

[twincamman]

When I inadvertently switched the cams and timed on 4 TDC the engine got more glitter than a stripper on 50 cent wing night ....Ed

[rgh0]

If you swapped cams and sprockets you would have problem if only swapped cams but put correct sprockets on correct inlet or exhaust then no problem if you assemble it right

[twincamman]

only the mixed cams, I used the correct gears on the correct side i did not want to reshim the cams ?..but it made the engine scary fast [as we old racers say ]] My chum found the engine in P,A, in a sports car wreckers . It was in the middle of a bunch of assorted motors .I immediatly took a day off work and drove there THe owner told me it was European spec race motor yatta yatta ?.he would have told me it was Attila the Huns personal race motor to sell it Im sure . bought it for 2500 dollars US did a rebuild bearings valves rings and pistons keeping everything labled and stored so I could reassemble everything in the same manner . After the rebuild I put it in 26R s2 33 . The motor always was slow to fire taking 4 or 5 revolutions and was adiquate for a TC I replace the carbs with a new set ?.put a new bushing in the distributor set timing read chicken entrils and had a Priest read threatening passages over it . All stayed the same bending starter ring gear teeth etc etc as posted here ,HOWEVER when I inavertanly mixed the cams up and set the number 4 piston as number 1 because I was too annoyed to re shim the cam some magic happened, It starts on the first 1/2 revolution ?.idles like a symphony ?gives a nice dark grey pipe .even with the junk gas we have now . thats why I believe the cams are not identical ?..similar but not identical ???the motor is faster than cow poop off a shovel now ?..ed

[rgh0]

Hi Ed
If you have never measured them for timing, lift and wear, don't use offset dowels to dial them in properly and they are of unknown origin from a wreckers engine then they could be anything and swapping them over may make the difference you describe for a whole bunch of reasons

However the original cams are identical and the dowel holes are different in the inlet and exhaust sprockets. So swapping just the cams and not the sprockets should make no difference if you have original cams in good condition.

cheers
Rohan

[twincamman]

Hi Rohan ...No I use vice grips to get razor sharp timing as I have no cams with adjustable timing dowels ?.Im not sure what happened but Im not changing a thing . The engine is just magic now . I have a spare set of cams I was / am going to use for a 1700 cc pushrod motor conversion to a T C when I can find a weber head .I will check the lift on all 6 cams and 2 engines some time . now its drive the car fix the car drive the car etc etc, weather here is only ok for English cars from April to Nov ?ed

[john.p.clegg]

Come on Ed,post your lifts and timing figures...give the rest of us a chance...

John

[rgh0]

Hi John
As a wise American friend once said to me
have a look at our dollar note it says

" In god we trust"

but it should also say - "all others please bring data"

cheers
Rohan

[twincamman]

Static timingis at 5 degrees to start and I set at 8 degrees,,,,,If I remember?. measure the cam over all length and the diameter of the cam casting subtract and divide by the lifter ??.im sure if I missed something there will much jollification in all the pubs in Britian and some Colonial sleazy taverns ..ed

[twincamman]

Ah Hell I'll just keep my data in my pants.......

[Jentwistle3]

Ho Rohan, John el al

I've spent some more time measuring and now have come up with:


Exhaust-
Opens 78 BBDC
Closes 2 ATDC
Lift (on the lobe) .348
Valve lift .338
MOP 128
Base circle 230 camshaft degrees seat to seat or 276 degrees at .050 lift

Intake-
Opens 34 BTDC
Closes 72 ABDC
Lift .348
Valve lift .343
MOP 109

Base circle 217 camshaft degrees seat to seat or 255 degrees at .050 lift

I've struggled a little with the base circle and have finally resorted to counting the degrees on the degree wheel as I rotated the engine through.

It looks like I need to retard the exhaust cam at least 10 degrees?
Thanks,
John

[rgh0]

By base circle I meant base circle diameter - the size of this will tell you if the camshaft has been reground. I suspect the inlet to be a regrind to get longer duration and more top end power and will probably have a a smaller base circle. The timing of it is about right.

Yes the exhaust cam looks like a standard Type C SE cam and needs to go back to around a 110 degree MOP which is 18 degrees change and close enough to 2 teeth.

I assume you not using offset dowels to set the timing precisely. You should be able to check the timing using the marks on the sprockets assuming you have original ones and one is marked exhaust and the other either has no mark or has inlet marked on it.

Do either of the cams have a groove machined into the boss the sprockets fits to ?
B cam no groove
C cam 1 groove
D cam 2 grooves
but most aftermarket cams had no grooves but may have a suppliers number stamped on the front face.

cheers
Rohan