Following on from the oil thrower question, the two manuals I have differ when it comes to setting the valve timing using the crank and cam wheels and timing chain.
Haynes says the dimple marks on both gear wheels must remain opposite each other with the crank is set at 12 oclock (TDC) and the cam at 2 oclock.
The MGB restoration guide says a staright edge placed across the dimples should pass across the centre of the nose of both the crank and camshaft.
With the dimples exactly opposite the straight edge misses the cam (which ends up at 3 oclock) and with the straight edge passing across the crank both dimple marks and the cam, the dimples are one cog apart (when viewed from the front).
Any advice greatfully recieved, unfortunately I forgot most of this stuff 20 years ago.........
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I would personaly do as Haynes says rather than anything else.bearing in mind you may find that when putting the chain on timing may be out on the cogs between 1/2-1 tooth out of line.I think thats around 2-3 degree on valve timing within limit as I remember.My mate has not long done his using Haynes manual and his was ok.
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My starting point on any engine I have ever done this job on is to check carefully what its present setting is before doing any dismantling. If it was running well with no indication that the timing was wrong, I tend just to mark the present set-up and then put it back as was. If that setting happens to coincide with say, Haynes, then I use that as a double check.
I've had engines (Triumph Roadster 1800 springs to mind)where I've found the markings looked nothing like the illustrations in the book, so I simply made my own marks and stuck to them.
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Thanks both for the advice - the dimples were one cog out when removed but the engine was not running well (symptoms are massive top end clatter coming in it at about 2500 rpm, and indifferent starting from cold) - the two issues may not be related of course but before I remove the head to check for burnt out valve etc I wanted to resolve this valve timing issue. I'll post the result when I crack this problem
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I believe for these engines the restoration guide is right. The usual BMC practice is to time the crank and cam by fitting the timing chain so that the dimples coincide with a straight edge across the centres of the crank and camshaft. If current setting is one tooth out, then you need to remove both wheels, reset the chain and refit. One tooth out on a timing chain will make the engine run most oddly.
Regards
John S
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Problem you may find is if a new chain is fitted you may have to fit new sprockets but that is no guarantee alignment will be spot on.I doubt one tooth out will cause any problems.But from what you said may possibly be oil feed prob to rocker shaft.ie very little or no oil to rockers.Just a thought but would look at that.
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Mech1
Are we missing something here? You can't get to the point where a chain driven cam is one tooth out and it's not capable of being corrected. This just needs the cog moved one tooth on the chain. To be honest I've always found chain driven cams to time up exactly.
Not being patronising mm-a, but the way to set this up is to turn the engine with the chain fitted 'till the timing marks are a close as they can get to being in line with a straight edge running between the centres of cam and crank. If they are, that's fine, the cam is set correctly. If you can't get them right, then get the crank wheel set so the dimple is in line with the straight edge you're using. Remove the cogs and chain, refit just the cogs and rotate the cam to align the dimple with the straight edge. Remove the cogs, and refit the chain and replace the cogs and chain on the crank and cam. It may need minute adjustments so they fit on the keys, but no more. Job done.
Regards
John S
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Slap on the wrist accepted.I stick by what I said.I have had the same with cambelts.Tr7 was right but as mentioned just a thought though being a long stroke it can`t happen or shouldn`t Appologies if it was misunderstood.I knew what I meant.Didnt explain properly.
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Just as a Ps.Has the head been skimmed am not certain about the stroke of it but have heard if head skimmed too far the valves just touch the pistons.could be but as I said not certain.so sorry if wrong?
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You'll not get the valves touching pistons on a B unless A. the heads been skimmed to death or B.the cam has been changed for an extremely uprated one. Normally on BL As & Bs you put the crank sprocket on and turn it clockwise so its dot is 90degrees from vertical and then turn cam sprocket so dot is in line with crank and cam centres. Then turn crank shaft the shortest way so that both dots on sprockets are adjacent and closest then remove both sprockets lay on bench and attach chain. Replace the whole assembly on to the 2 shafts without disturbing either shaft. Then rotate engine 2 revolutions clock wise and ensure dots line up.
Jim
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I don't know if this applies on this engine, but engines I have known with chain drives, you can reverse the sprockets to get 1/2 tooth timing, or move the sprocket round 90 degrees on the cam to get 1/4 tooth.
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The dimples should line up with the straight edge across the centre of the crank and cam shaft. However if the head has been skimmed then there will be miss alignment as the free lenght of chain is fixed but the shafts have closer together. From memory the free length is on the right ( tensioner on right ) so with Crank at TDC the cam dimple will be slightly anti clockwise of the mark. ( to the right at the straight edge. ) Regards Peter
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