The Triumph Dolomite Club - Discussion Forum

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 Post subject: cam timing
PostPosted: Wed Sep 22, 2010 8:09 pm 
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Can anyone help on this one.My sprint has a fast road cam,vernier,standard carbs and exhaust at the mo. Shimmed up to 10 thou ex 9 thou inlet, idle a little lumpy but there is a flat spot from 1000rpm to 1500 which can make pulling away awkward.I have checked timing which is correct,tried another cap and leads,checked the carbs over but the problem persists. I have noticed that the notch on the cam is not quite in line when the crank pully is at the tdc point, but the vernier is at its max adjustment unless i remove it and re/align the whole lot, the car seems down on power,pulls ok but not as well as standard sprints i have owned. Question is,i dont think im getting full lift and i dont have a timing disc, how accuratly can i get it , may revert back to standard :( ps car on magnetronic


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 Post subject: Re: cam timing
PostPosted: Thu Sep 23, 2010 4:24 pm 
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Joined: Sat Nov 25, 2006 10:46 pm
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You should first check a few basic parts, and procedures.
With the vernier sprocket almost out of the adjustment positions, adjust the chain first with the chain tensionar in the full home position, you need this red U shape plastic tool for that also.
Now adjust the chain with the curved chain guide. Yes the front cover has to come of. Only if your 200 % shure the chain had been adjusted IN THE CORRECT WAY recently you can skip that part.

A timing disk is everywhere available, every Kent cam comes with one, so I'm sure they can sell you one.

Be absolutely sure that the timing mark on the front cover is right, have seen to often they are not.
To check you can use the same clock as you will need to check and adjust the cam at max lift, (depends on the cam) mostly 106 108 degrees ATDC.
You have to use a long pin on that clock and go simply trough a sparkplug hole. I do this all in forhand when the head is still of but that is no option now.
After finding the real TDC mark it on the flywheel if the engine is out, and on the front cover as well.

If you have a cam with on the end a kind of bold pattern 6 side, your lucky, you can use a normal spanner to turn the cam inside the vernier sprocket till max lift.
If not, it can be a struggle to adjust the cam, you have to fight 16 valve springs.

BTW picture of a lichtly tuned streed engine, no racing engine

Hans

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 Post subject: Re: cam timing
PostPosted: Thu Sep 23, 2010 7:02 pm 
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Thankyou Hans ,some of what you have suggested i have already tried. If i find true tdc with plug out and thin tool in the plug hole ie bring the piston up and judge its position if i then line up the cam to the mark would this be ok,i know it is not the right way but everything else has been checked. The chain and tensioner are new as are the pistons,rebore and cross drilled crank etc. Its only the revs in this range that spoil the car, i drive a turbo diesel ford mondeo so i hope i am not used to that power and judging my sprint against it,thanks once again.


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 Post subject: Re: cam timing
PostPosted: Thu Sep 23, 2010 7:54 pm 
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Location: Weston-super-Mare, England
You can't use the standard timing marks as you have a different cam.

Find true TDC using a dial gauge. Turn crankshaft 106 deg. ATDC ie. clockwise. Set inlet valves on no.1 cylinder at their fully opened position using a dial gauge & mark this position. (All as per what Hans just said). :D Make sure the timing chain is taught between the crankshaft & camshaft sprockets ie. the right hand side of the chain.

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 Post subject: Re: cam timing
PostPosted: Thu Feb 03, 2011 10:21 am 
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Location: Hobart, Australia
Is there a trick to determining the precise point of max lift? It seems to me that there is a range of around 10 degrees where a dial gauge won't move at the point of max lift?
(I thought about using the trick where you measure the angles at which you get 50" less lift on each side of the lobe, then dividing by two - but that doesn't work with an asymmetric cam....)

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1975 Dolly Sprint
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 Post subject: Re: cam timing
PostPosted: Thu Feb 03, 2011 1:40 pm 
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Bring the cam up to max. lift & until the gauge doesn't change then make a mark on the cam. Then go past the max. lift & rotate it back the other way towards max. lift & make another mark on the cam. True max. lift will be mid way between these two marks.

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 Post subject: Re: cam timing
PostPosted: Sun Feb 06, 2011 9:01 am 
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Thanks Mart, that's now one thing i can cross off the list :D

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1975 Dolly Sprint
1973 Fiat 124 Sport CC (SOLD)
2008 Golf GT Sport TDI

2008 Triumph Daytona 675 race bike
2008 Triumph Street Triple
1989 Honda CBR250R race bike


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 Post subject: Re: cam timing
PostPosted: Sun Feb 06, 2011 9:50 am 
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I'm glad you understood what I wrote...I didn't :woohoo:

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2007 Porsche Boxster S


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Grammar:
The difference between knowing your sh#t and knowing you're sh#t.

Schedule: Pronounced "Shedule" not "Scedule"!


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