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Timing chain alignment


SeanG
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Good morning folks, 2 days ago I changed the usual timing chain, tensioner, ring, etc kit for my GT6 MK3. (89K)

Here is picture before/after.

Anyway, I have a doubt now  :ph34r:

When I changed the chain, i didn t remove the sprocket crankshaft, only removed the camshaft one, when got it back with new chain, i carefully tried to align the dots, but now i got a doubt, that i may have rotate the crank a little bit without the chain so camshaft would have been "unsync".

 

So yesterday, I checked TDC, and when the pulley align with the mark on the timing cover, piston no1 is at max, and if i rock the pulley, piston no1 will only come down either way.

I suppose TDC mark is good then right ? but what about the camshaft ? is there a way for me to check ? 

while back someone told me for my MGB that to find exact TDC is when valve no4 is rocking, is there any way for me to check that crank and valve are "sync" with a similar method ?

 

please don't tell me to buy a timing disc and start from scratch  :P

 

sorry for mega post !

post-1175-0-25511800-1435302966_thumb.jpg

post-1175-0-68625600-1435302970_thumb.jpg

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with rockers  set to 0.010"    turn to get 11 12  equally on the rock , inlet comes up , exhaust going down,      set 1 and 2  tappets at 0.040" 

 

turn crank to N01 firing TDC   the tappet gaps  on 1 & 2 should be the equal ( gap is not known) 

if they are different the gear needs indexing   ( the 4 holes give 1/4 tooth increments)

 

Pete

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Thx a lot for help, did everything you said and unfortnately at the end, tappet no1 let a 0.08 gap in and no2 is blocked for same size...

Does that mean have to open cover and re align everything ? Is the timing disc the only way ?

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Hey pete i ve just done this, found on other forum :

 

You don't need "timing figures".

Do it by the "Equal Lift on Overlap" method.

 

Most camshafts, inc. Triumph ones, are symmetrical. The Inlet and Exhaust cams have the same shape and those for one cylinder are spaced symmetrically about the TDC position. Also, the cylinders are in pairs, exactly 180 degrees out of phase. So, as No.1 cylinder reaches TDC on the firing stroke, No.6 is finishing the exhaust stroke and starting the inlet stroke of a new cycle.

 

Method:

Set the crank at TDC for No1 and No.6.

Set the camshaft so that the cams for No.6 are both equally lifted - Exhaust going down, Inlet going up.

Fit the cam chain.

Voila!

Trust me. That is all, and your camshaft will be perfectly timed.

 

John

 

 

All went well, the marks on teeth aligned as well, then i re did your test with tappet 1 and 2 at 0.040" and still same problem, 1 is open and let a 0.008 in and the no2 is totaly closed, am i doing something wrong here or the info from the other forum is wrong ? Thx a lot for precious help

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It makes no real difference if you check 1, 2 or11,12 the principle remains the same to get two opposing lobes equal each side of tdc on the cam with the crank at tdc for the same pair of lobes

either on its max lift or its back

 

To get the cam lobes accurately you need to put a dial indicator to measure the lift and a card disc protactor on the cam shaft so you can get equal lifts an mark the disc, mark halve way between the two is cam lobe tdc

 

 

note on some later cams you turn the crank back 2 degrees from tdc

 

 

As you have pre scribed alignment marks these really should work providing you keep the chain drive side taut and dont turn it backwards

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well thats assuming the dot is factory fitted , the scribe line looks poorly scribed .

 

   aligning the dot and crank centre line is a std method of the day, triumph in there wisdom decided to improve setting from a wide  ( about right )tolerance with a dot ,to having the pairs of bolt holes made to allow incremental and very accurate setting,  as said each pair will index 1/4 tooth and then turn the gear over and you get another pair of 1/4 tooths 

 

the problems of accurate cam timing come about from there's a  good amount of cam lobe rotation without any change in the lift and to be correct 

you need to get the  same cam  lift at say ( clock face) 5 to 12 then 5 past twelve and  split the difference  for exact cam tdc

 

the dot could be less accurate , depends how its position was determined 

 

if that makes it clearer or cloudy   

 

its a lot easier to do than talk about and many manuals dont get it quite right

Pete

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in my pocket    ha !!

 

most manufacturers  did a dot to dot ,  but the result depends on the tolerances used in the manufacture of the crank gear and its keyway and the cam gear and its fixing, some were also keywayed , makes it easy

 

the triumph idea of having  4 holes useable in 4 sets of pairs Ive not come across elswhere ,  its good idea once youve got your head round it 

as said the max lift on a lobe can cover quite a lot of rotation without changing the lift so getting tdc cam lobe is always a bit of time and thought 

consuming 

then throw in later engines had the crank backed off 2 deg just  to sell stronger tea bags 

 

what happened to the simple life.....Ive just worn your beads out .... and they scattered from a hole in me pocket 

 

and the wifes  got the vac out  !!!

 

pete

 

 

 

 

Pete,    

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