beer talk

Over a pint or two the great subject of cam timing cam into force...the debate was what happens when the cam is advanced or retarded.
the answers where quite differant....
So how would the engine respond to 50 degrees's advance..and say 50 Degree retard. what effect on compression air/fuel,mixture etc...i except only a few will have played with adverse timing...mayby some by mistake.

For crying out loud, 50 degrees? Is this a trick question? After some serious clash I think the rest of the question would be void other than the compression part which would be nill.

How about something closer to reality like 10 or 15 Degrees.

Although my comments will be simplistic compared to other when they respond, the timing characteristics will depend on a particular cam I'm sure but generally speaking,

It was my finding that retarded cam raises the compression at kickover but kills rpm obove 3500 or 4000 whereas advanced cam lowers compression on kickover and bringing the duration of the stage 1 cam into play for higher RPM running. My JS cam is 10 degrees advanced.

I expect to have to diddle Peels drag cam to live with on grass and Gravel steeps. Mostly only have to think of the intake valve points of opening and closing. If cam advanced the valves close sooner so helps trap in more mix at slower rpm but then stifles the inertial mixture rushing in at higher rpm. Retard closes intake later so less effective compression stroke and tends to bleed back pressure at lower rpms but traps it at higher rpm. Can only diddle so much up or dn on hot rod cams before valve clash with pistons. 50' should not be possible on Nortons and 10-15' has a lot of effect as already mentioned. I've done V8 dyno test moving cam a few degree's at a time til last best power curve gotten with just mere half a degree advance. The side note of degreeing is generally cams ain't as perfect as advertised so must compensate some up or down for best joy. Now if we could only alter the intake and exhaust separately we've have even more fun.

Peel had vernier adjuster and I tried to move cam like 3-5' to see what happened but valves hit piston and realized I didn't know enough yet so will try again someday with forum guidance. Vernier's now scare me as the lock pin can come loose so can't recommend them and likely reason they are so rare in long term hard run Nortons.

Some modern auto engines have variable cam timing. My Ford 4.6 liter has it. When the cam shifts (I think more advanced at cruise), I see about 200 RPM drop. In actuality, I believe the engine wants to run 200 RPM faster, but the cruise control maintains speed, forcing the RPM to drop, the result is more like a subtle up shift. When encountering a hill, the reverse happens, the cam shift is more like a subtle down shift.

I don't know how many degrees the cam motors can move, but I would guess 20-30 max.

Slick

I bought a 73 Commando that had the cam one tooth off, retarded. It ran but had no power down low. It would barely make it up my driveway. Once under way it went down the road and I drove it for a while like that until I realized what was wrong. Way down on power the whole time it was retarded though.

"Beer Talk", good choice of conditions for this topic. When I worked on these bikes a few years back, a good friend and customer wished to tackle his own resto on a 750. We sold him parts and helped over the phone and face to face as much as possible. When the two year project was done he'd turned out a pretty respectable example....that would not run right. Started well, idled pretty good, and had OK power 'till 4500rpm where it fell flat on it's face and started missing, farting, coughing back through the twin Amal's. Poor guy would show up in the morning talk ignitions with the boss, go home with a new Boyer, came back in a day or two with no change. Then he and the boss would talk carburation, and he'd leave with slides of a different cut-away. Next day, no change. Then new Amal's, no change. Almost a whole season went by for him like this, but when I heard he and the boss talking "maybe single Mikuni or Amal" I came out of my area and asked if I could take a look. Boss gave me a "don't you have something to do" look. That evening after work though, I stayed and after checking his work on all the other try's, I checked the cam timing. I honestly don't remember in which direction it was off, but it was off two or three teeth. Put right on the factory specs sure put the snap back into that 750, all the way up the rev range. When the owner came by the text day, he had his usual, "I don't expect much improvement" demeanor". I said "I don't know man, give it a whirl". When he came back from that ride he was like a little kid that just got his first two wheeler for Christmas....And I got a nice case of nice beer. That's what I know about cam timing, for best results put it where the factory says to on a stock motor. :mrgreen:

Will over advance or retard cause the fuel mixture to become weak,or rich?

texasSlick said:

Some modern auto engines have variable cam timing. My Ford 4.6 liter has it. When the cam shifts (I think more advanced at cruise), I see about 200 RPM drop. In actuality, I believe the engine wants to run 200 RPM faster, but the cruise control maintains speed, forcing the RPM to drop, the result is more like a subtle up shift. When encountering a hill, the reverse happens, the cam shift is more like a subtle down shift.

I don't know how many degrees the cam motors can move, but I would guess 20-30 max.

Slick

Click to expand...

I think what you're seeing is indeed being done in the transmission. Cam timing change alone would not have any influence on RPM vs speed in gear.

As the beer drinking advances, the opinions become retarded. That's my experience.

rvich said:

As the beer drinking advances, the opinions become retarded. That's my experience.

Click to expand...

+1
John, I think it's about 8pm there now. You must have started a little after lunch? Better drag it home and re-read this tomorrow.

John said:

Will over advance or retard cause the fuel mixture to become weak,or rich?

Click to expand...

I don't think so, but it may affect octane in relationship to combustion.

OK it's time to come clean, i should'nt have posted this on the commando forum...and will except a big slap from the moderators!
Truth is i have been working on a 1936 Morgan ..Jap 1000cc dog eared water cooled V twin ...single amal carb T branch ...evey thing {so far] checked out...compression 100psi and 120 psi spark timing same both side 680 thou and 700 btdc ...But it runs crap! colour tune shows yellow oneside ...RICH as hell with cool header,,,other side pale blue WEAK as hell...red hot header....can incorrect cam timing cause this? the 120 psi is on the weak side..is the lower compression[100] due to bore wash? all joints made air tight with tape...

At least post a photo!

I like beer,
that is all.

Vince

I do my best thinking while in the shed drinking, I come up with all the right answers, but I put the tools down after 6 cans of my favorite brew XXXX Bitter, but I have to write down what I have been thinking as after about the 13th can my memory go a stray, but when my mate Paul comes and helps me emty the beer fridge we nomaly solove all the world problems.

Ashley

Just guessing on the Morgan Vtwin that d/t the off set crank firing two jugs fairly close together that one is getting extra dose of mix its stealing from the other. No idea if ya can set its cams so one jug sucks in better than the other. If ya can't figure it out I quess it means ya bit off more than can chew like me at times and picked wrong hobby for easy fun.

" spark timing same both side 680 thou and 700 btdc "

What the hecks this ?? I find the beers best left untill the jobs finished . Properly . and the tools put away .

680 thou. points gap sounds excessive , and 700 btdc would be 20 atdc , so its retarded . Retarded Ign. will get the pipes glowing .
If you turn out the lights . :x :twisted:

o.k. , ACTUALLY , checking the Overlap = as in plugs out - turning to each valves approaching the seat , one opening one closeing .
a few pencil marks somewhere that goes around , as ea seats / unseats - a mark half way , and IT should come up at or a few degrees
BEFORE tdc . But ONE step at a Time . Checking the tdc mark is one step - estabishing the opening / closeing OVERLAPP is entirely differant .
Even though theyre both on the same engine .

Knackered Plugs or a Mouse in the intake manifold could be other causes .

A weak spark is like warm beer , thats gone flat and stale . It wont go off with a Bang . More like a damp squib . :!:

Send the J.A.P. to ME , and install a CX 500 Honda Engine . FAILING THIS , a phew fotos might make amends meanwhile .
I fink your mag. might be munted .

P. S.

photos of the J.A.P & Morgan . NOT the Beer . please .

Years ago I has a flat twin in bits, but when putting it together, I could not determine how to get the timing marks to line up. I was 1 tooth out on the worn chain [ which could have been less than 1 tooth advanced as a result ]. The engine had no power and used fuel like the Saturn Rocket. Effectively, the engine ran ok with the cam slightly retarded as a result of the worn chain.
Moral of the story. Don't F--- with the timing.

john robert bould said:

Will over advance or retard cause the fuel mixture to become weak,or rich?

Click to expand...

accept it. IT WONT RUN RIGHT

john robert bould said:

OK it's time to come clean, i should'nt have posted this on the commando forum...and will except a big slap from the moderators!
Truth is i have been working on a 1936 Morgan ..Jap 1000cc dog eared water cooled V twin ...single amal carb T branch ...evey thing {so far] checked out...compression 100psi and 120 psi spark timing same both side 680 thou and 700 btdc ...But it runs crap! colour tune shows yellow oneside ...RICH as hell with cool header,,,other side pale blue WEAK as hell...red hot header....can incorrect cam timing cause this? the 120 psi is on the weak side..is the lower compression[100] due to bore wash? all joints made air tight with tape...

Click to expand...

A good rule of thumb for valve timing, is that with the eye-ometer, the exhaust valve will be nearly closed and the inlet valve will be just open at TDC. If there were no obstructions to turning , the cam would be sitting balanced with the spring tension of both valves holding it, then that's where TDC will most likely be. Anything else and you can be sure the timing will be wrong. This can easily be seenwwith a regular OHC 4cyl or push rod OHV engine. With the commando, you need be able to feel the rockers on one cylinder moving away from closed as the engine is rotated either side of TDC. Need 2 people for this.

Have fun.