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MG MGB Technical - Fitting timing chain

You all know the problems I have had and I thought I have found the solution but there is always someone to put the frighteners on you, one member has said that one tooth out on the valve timing will not bother an MGB as it would only be at the most 3Degree's out what are other members feelings about this remark also it says in the book that to put a straight edge thru the centre of the cam shaft and the crank shaft and the dots should be in line. The problem there is the crankshaft nose sticks out about 1-2" and it makes it very hard to judge this is with crank at TDC and if simplex chain camshaft key at 2 o' clock. I think mine is more than one tooth out but I am waiting for a new chain before taking the old one off, also I know I may sound stupid but again in the book it says assemble the sprockets with the dots in line then slide them onto the shafts if it doesn’t fit move the cam shaft then check alignment of dots thru centre lines put tensioner back but surely when you turn the engine one revolution wont the tensioner by taking up the slack in the chain i.e. shortening it move the sprockets out of alignment and then the dots wont line up .When you put timing chains on Jags etc you have to compensate by moving the cam sprocket a tooth at a time until they line up when tensioned and the engine turned over many thanks Tony
t_basham@hotmail.com

I haven't counted the teeth on B timing sprockets, but on a midget, one tooth out will move your timing 18 degrees. I can't see the B being much different.

I had driven my brother's Midget and thought it was a bit 'flat'. When I had the engine out to replace the clutch and do a few other jobs, I checked the cam timing, just out of curiosity. Instead of giving full lift at 110 degress after TDC, it was at 133 degrees...a full 23 degrees out! I moved it one tooth to line up the dots and got it to 115 degrees, which is good enough for a road engine and as close as the factory would have got it.

On a race engine I would have used an offset woodruff key to get it as close as possible.
Dave O'Neill

DAVE-Can you give me an answer to my other part about the tensioner when released moving the timing marks out of position and how you can put a ruler across the centre of the shafts to see if the dots are in line with each other when the crank shaft is miles longer than the cam shaft. re the tensioner as i have said on all other cars etc you usualy put the cam sprocket one tooth out so when you release the tensioner and turn the engine one revolution every thing is lined up when the slack is taken up by the chain or belt or is it me who is going loopy regards TONY
A Basham

Tony, according to my manual the only time a straight edge is used is to check that the crankshaft and camshaft gears are in line so that the chain is running true. If they are not, shims are inserted to align them. The timing is fairly simple;

crankshaft turned until key way is at top, camshaft so that key way is approx 2 o'clock, fit chain to gears, line up dots on gears, fit gears to crankshaft and to camshaft and turn camshaft if required to keep the dots lined up.

No mention of offsetting the alignment to account for chain tensioner operation. I have carried out this procedure many many times on Mini 'A' series engines and it is easy and straightforward. Can't see any difference between the 'A' and 'B' series as far as this goes.

I think you are looking too deeply into the matter.

Cheers

Tony
Tony Oliver

A I think I know what you are worried about ,no worry it sounds more cpmplicated the it is,For the most part the tensioner is important as the chain stretches, when you put the chain on[new]its rather tight with less the a links lenght "play"
Ric
Ric Lloyd

It's vitally important that the teeth are lined up properly. One tooth out will not do and will result in you getting your low vacuum reading. Fit the gears to the chain on the bench and get the marks in line with the straight edge running right through the centres of the holes. Now lift the cogs on to the shafts turning them if necessary to get the alignment to match the gears. Fit the tensioner the tension from which will make no difference to the chain setting and must not be compensated for.
Iain MacKintosh

Iain, I can't agree with you on one minor point. The only shaft you should turn is the camshaft. The crankshaft must be at TDC. Apart from that you are spot on.

Tony
Tony Oliver

Tony,

Go and look at http://www.octarine-services.co.uk/enginebuilding.htm
Sections 4 and 5 have a picture guide to what is described above. I found this guide very helpful when building my engine.

Iain
I D Cameron

Tony, no need for the crankshaft to be at TDC since the alignment of the cogs to chain governs the alignment. In addition it's probably easier to rotate the crankshaft a little to get the cog to drop onto the camshaft. However once both gears have been installed the crank will be turned in order to check centrelines.
Iain MacKintosh

Whilst the books do show a straight-edge being *used* to check the gear alignment they also show diagrams of the shafts and gears with a straight line *drawn* through the shaft centres, the dots on the gears, and in the case of the single-row chain the camshaft keyway. It is that alignment I have been recommending Tony to check. Also that until Tony uses a timing gauge to measure his valve opening and closing points he has no idea what cam has been fitted, and until he has verified that the valve timing is correct there is little point chasing anything else with this long-running low vacuum and poor idling saga.
Paul Hunt 2

Absolutely right, if this cam has different timing to standard or is a high lift configuration then the vacuum will be lower than standard but I very much doubt whether as low as 11Hg. I think that most of this is down to incorrect cam timing. Either way the whole thing needs to be thoroughly investigated.
Iain MacKintosh

This thread was discussed between 28/01/2007 and 29/01/2007

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