Britbike forum Forums British motorcycles in general British motorcycles in general Lobe center with the head on

Hi; I have this engine that I do not want to remove the head but want to check the lobe center.
I think that is possible to obtain good numbers with the head on and put the clock touching the valve tip.
Regarding the fighting with the springs tension; what would be a good method?
Nil clearances?

-I tried to search something but the search algorithm in this site is almost useless. I mean; why if I write T140 LOBE CENTER do not show any thread about that but shows whatever?


Thanks

sure uou can do that, fernando.

get a socket for the cam wheel nuts, and a long breaker bar so you can turn against sprimg pressure.

set your valve clearances at some low value and use the normal technique

Search engines are not conversational. They look for words. I put in "the" and got 2000 hits. You need to narrow the words in your search to what is relevant.
It appear the only way you can change the timing is to pull and replace the intermediate or crank gear. When you do that the valves will have to all be closed. Off hand I d not know if that is possible.

just checking you can leave the idler on. even leave the timing cover on, if you put the degree wheel on the primary.

to chsnge timing you have to heave ho on the breaker bar to rotate against spring pressure with the idler out.

fighting the springs is a pain, especially whem you get one cam set and have to hold it still while uou use the bar on the other.

vastly easier with the head off.

Hi Quinten; that article do not talk about what to do with the springs and valves (head on)

Hi Kevin; may be the solution is to check without removing the head; if the timing numbers are not good; then remove the rockers and head and proceed.

Hi DMadigan; as mentioned "T140 lobe center" is a narrow search in my book; but not on the search function because nothing similar appeared.

you can jack up the rear and turn the motor with the rear wheel in fourth gear too. you dont need to see the timing marks to do this. set the degree wheel to match the crank position, put the dial indicator on the valve collar, and then just check lobe center in the usual way.

try searching on this string, fernando

+T140 +"lobe center"

use the quote marks to group words that must be together, and use the + symbol to specify that a term must be present.

...yes that was what I would do. I have fifth gear as top gear.
By the way Kevin; I saw a photo of one of your timing settings where you choose 104º intake instead of 99º. Is not "100" an "ideal" number for the intake?

so they say.

but my machine is faster by not using the "ideal" numbers.

106 is even less ideal and even faster.

An easy way to check with the head on and push rods in place.
Remove plugs and install degree disc
Using a piston stop, set disc TDC
Set tappets to something like 0.025" using feeler gauge, the actual number doesn't matter but it is essential to set inlet and exhaust to exactly the same
You can now rotate the engine and find the opening/closing points using a 0.0015 feeler, the tappet just nipping the feeler. Note down the opening and closing degrees
The lobe center is half way between the open and close degrees

...still waiting due to cannot remove pressure plate to lock the clutch and all that to place the degree wheel... I cannot have the special device to hold it in the timing side.

A bit of flat bar fitted between the drive sprocket teeth the cutch drum teeth will do the job qiote well
A deep offset ring does the job better
You can glue a magnet to a cheap timing wheel and stick it to the end of the crankshaft nut if you are just taking measurements
The magnets from old hard drives are perfect for this
Watch your fingers .

Good about the magnet; not so good that I have no one so big to hold the degree wheel tight to prevent movements when turning the engine.

Old computer hard drives
Old VCR hard drives
They are a dime a dozen
Takes about 10 minutes to pull one apart
They will hold the std plastic timimg disc quite tight
Other alternative is to print one onto a self adheasive lable
Reduce the size so it is the same as he rotor then sut it out and stick it to the rotor
Down side is the marks will be very close together .

Asked the same search question in faq forum. If you put the words in quotes it will only look for threads containing that phrase that you put in quotes not any and all of the words. Such as "t140 cam lobe center" you may get no hits unless that exact phrase is used but it will perform more like Google ( that everyone expects it to) (including me)

Why not simply use Google? It will turn up lots of results from this forum, and quite a few others to booth.

SR

Hi;
the TDC would be in the compression stroke to start to check? or would be in the intake stroke? (for the intake at least)

No body mention that and I obtained odd numbers and I think there are related to the reading of the disc in relation to the TDC and in which way the valve to check is.

-Is not moving the engine forward and just that...

Thanks

For inlets the inlet valve will start to open at the end of the exhaust stroke, maybe around 15° before TDC. You’ll then have 180° of crank movement where the valve is open, the inlet valve will then close around 15° ish on the compression stroke so this will be ABDC, you’ll have around 210° Inlet duration with those figures.

To find the LCA, half that 210 (so 105°)

Then deduct the first 15° off that 105°, so the LC will be at 90° ATDC on the induction stroke. Stick with ATDC, as some cams will read 102/103 (102° ATDC induction, 103° ABDC exhaust. All cam figures will be given in ATDC and ABDC)

For the exhaust stroke it will start to open say 10° BBDC, again that will follow by 180° of crank movement as the crank goes through its exhaust stroke and it will close say 20° ATDC,

So you can see that you have about 35° of valve overlap, total duration is the same for exhaust at 210°, but…

10+180+20=210

210/2 = 105

105 - 10 (degrees from BBDC) = 95° ABDC LCA

Those figures are probably more accurate at 80 thou lift where the valve is starting to open much quicker than at 040 thou. At that you can be more accurate.

Mega cycle figures at at 040 thou, doesn’t matter which you use as long as you calculate the LCA from not only your figure but those given by the cam manufacturer.

Also once your degree disc is correctly timed, it is set for both cylinders.

...so TDC would be set in the intake stroke; with what you say; however, I obtained 43º at 0.040 opening.

A good timing disc will have marked TDC and BDC, find true TDC and align the disc. Don’t use something printed off, get a decent aluminium one.

When you find your 040 lift, note the value and it’s relation to TDC or BDC

The intake valve should open BTDC

IT will close ABDC

...yes; I did that (remember that the engine is assembled)
You see in the photo that the TDC mark is at the right and the 43 is at the left scale; I saw that in other guys the TDC mark is at the left for the inlet opening.
I do not understand that due to if I have the crank at the TDC mark then move it to the 38º BTDC mark, I obtain the TDC at the right and the 38 at the left; as I obtained the 43º
Why others obtain the inlet opening at the other part of the scale?

Thanks

Hi Reverb, type the following in a Google search. The results may be helpful.

lobe center site:britbike.com

I would also add quotes around lobe center.

I assume you have the bike in top gear and rotating the engine forward with the rear wheel?

Viewing the crank from the drive side the crank will rotate Anti Clock Wise, so your image is correct for valve opening. This is 43 degrees Before TDC,

Your ignition timing should also be at the same side of the TDC mark (albeit about 6 degrees less than what you are now but on the cranks next rotation instead)

When you do your valve closing, you will find it easier to rotate the cam until there is no lift showing (so the follower is running on the base circle section), then rotate the engine (cam) back beyond the .040" lift mark on the dial gauge, then rotate it forward until 0.040" is shown. By rotating it forward again you are taking up the lash in the timing gears, by finding the end of the lift cycle initially you are not counting the amount of times the dial gauge spins full circle at a fast pace to then have to count it coming back down again.

HTH