m40 cam belt tension

[keen 6]

Can anyone tell me the correct tension to be put on the cam belt when replacing with a new one or better still how to put the correct tension against it. This is on the m40 engine

[hotwire 352]

Wheres Mr Lawrence aka Silver fox when he's needed....

[Silver Fox 43]

OK, so I've got another life actually.

You need to lock the cam in the right position, tighten the toothed cam cog on the front with the tension tight on the right side as you look at it from the front, and then lever the tensioning cog out till the belt will twist to 90 degrees with your fingers. Tighten up the nut on the tesioner at this point, you should be left with around 10mm of slack in the longest run on the belt. Quite easy really.

[keen 6]

OK, so I've got another life actually.

You need to lock the cam in the right position, tighten the toothed cam cog on the front with the tension tight on the right side as you look at it from the front, and then lever the tensioning cog out till the belt will twist to 90 degrees with your fingers. Tighten up the nut on the tensioner at this point, you should be left with around 10mm of slack in the longest run on the belt. Quite easy really.

thanks for that I have made up the tools that you recommended to lock the cam and the fly wheel. it was the tension that concerned me as one of the dealer serviceman said that it needed to be quite tight, and I wondered what he meant by "quite"

[Silver Fox 43]

Yeah, quite tight is a matter of opinion I guess. Over tightening is not good either. Like I said, all the people who should know have told me the 90 degree thing is the best way if you don't have the correct BMW tensioner. Hope it helped.

[keen 6]

The process has been slow but methodical, And now I.I've come up to another situation. the cam cog has only one mark on it.Its on a tooth, but there is no marks at all on the outer casings to give me a position for the tdc with the crank.So I have put the camshaft so that the 1st lobe is at about 11 0clock looking at the front of the engine.And the cam cog mark is about the center line of the engine.The cam tool holds it there, I realize that it could be in one of 4 positions, but this one seems correct. Is it ?

[Silver Fox 43]

There is a notch on the housing at the top around 12 o'clock, the mark on the cog should line up approx on it. Make sure it's the firing stroke not the exhaust one. ie. both valves should be closed on no. 1 cylinder.

[keen 6]

OK Ive got only a step in the molding in which the plastic covers come up to .Is this the mark that we are talking about it is about the 12 O'Clock position. there are no other marks that I can see. The 2 cam lobes are 11 O'Clock and 1 O'Clock a putting the valves closed. the rear ones are down I assume they are open or opening?

[Silver Fox 43]

The notch to line the mark up with is the double ridge, about 20mm past the end of the plastic you're looking at, heading to the top or your right from the front.The cam alignment tool will tell you when you're there anyway.

So long as both valves on 1 are closed and the cam is held in the right place you should be good.

[keen 6]

The notch to line the mark up with is the double ridge, about 20mm past the end of the plastic you're looking at, heading to the top or your right from the front.The cam alignment tool will tell you when you're there anyway.

So long as both valves on 1 are closed and the cam is held in the right place you should be good.

thanks on to it tomorrow

[keen 6]

It fired up 1st turn of the key, ran a little rough for a second then settled back to a normal idle and full oil pressure straight away.Thankyou for all your help. It would have been the perfect job except for the engine rear water/heater outlet.The housing had corrosion in it and there was a hole half way back from the end. I thought that I could fit the hose on far enough up the pipe to cover it but the water leaked passed.So I will have to get another housing from somewhere and replace it. But otherwise all was perfect.The two tools one for locking the flywheel, the other for locking the camshaft were just fantastic, and they were easy to make too. Ive no doubt that these help make the job easier and faster.I was a little concerned about the specified advice with the head gasket, in setting the head bolts in 1st 30nm then two sets of 90 degrees.there was some bolts that were definitely tighter than others,I would rather set these to a specified torque value next time. I'm not sure that I should check these again later or not.but otherwise the whole job of new head gasket and cam belt went of without a hitch after finding out the correct information from you thankyou Ken

[Silver Fox 43]

Real good to hear Ken, pm me your address and I'll send you down the piece you need, got a few of them here.

ps, you should tighten the head bolts another 25 degrees after half an hours running.

Edited April 27, 2008 by Silver Fox

[keen 6]

That sounds really great what does pm mean? Put my address here or somewhere else?

[Silver Fox 43]

Click on my username and one of the things on the list that drops down is to send me a message. That's a pm, or personal message. Click on that and send me your addy, that way no one else gets to see it.

Cheers.