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by Mal Marsden - 06/16/22 7:00 pm
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Allan G, Hugh Jörgen, kevin, NickL, pushrod tom, Tommy Thomas
Total Likes: 8
Original Post (Thread Starter)
#865243 12/04/2021 8:03 PM
by reverb
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?

Liked Replies
by kevin
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.
1 member likes this
by reverb
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.
1 member likes this
by Andy Higham
Andy Higham
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
1 member likes this
by Allan G
Allan G
Originally Posted by Hugh Jörgen
Originally Posted by henryanthony
-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?


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

lobe center
I would also add quotes around lobe center.

And double check spellings, my phone auto corrects to "love centre" laughing
1 member likes this
by DMadigan
Maybe I am miss interpreting this:
"With 4T I wanted to say the events (intake compression; power and exhaust) so if I started rotating the engine forward at the intake stroke (pistons go down) and the intake valve starts to open; I obtained those 43º; after at what point should I stop?"
Are you saying you are looking for the intake valve to open after TDC? The intake opens before TDC.
You should work with the lobe centre and not opening/closing angles. that way you do not have to worry about exact measurements of small lift.
Use the crank locking tool to set the degree wheel or measure the piston near the largest range of your dial indicator, less error induced.
If you do not have the cam opening/closing numbers, read the crank angles at half cam lift and calculate the lobe centre from that.
Otherwise for intake:
(BTDC + 180 + ABDC) / 2 - BTDC is the lobe centre ATDC
For exhaust:
(BBDC + 180 + ATDC) / 2 - ABDC is the lobe centre ABDC
1 member likes this
by Allan G
Allan G
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
1 member likes this
by pushrod tom
pushrod tom
Or, so long as you can get your indicator on the valve well enough, set the lash at 0 for E and X and take readings at .060 and figure your centers from there. This should give you repeatable and consistent results.
1 member likes this
by Hillbilly bike
Hillbilly bike
Yes, what Tom says, no lash....This cam timing on a Triumph is best when done with the rocker boxes off, dial indicator on a push rod. Use a hand made wire guide to keep the pushrod alligned as you cycle the engine...You may not be able to get around 100 degrees with just the three keyways. You may need to advance or retard the cam gear one tooth and then try the keyways....Work slowly, and carefully and when frustrated, walk away for a time....
1 member likes this
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