Any Advice, Part 2!

[Othen]

Originally Posted by Laird Scooby

The timing belt should ONLY be retensioned ONCE after 600 miles and it MUST be done at TDC on #1 cylinder.

Good morn Dave,

Many thanks for this - Chris and his son have a really interesting project here.

I'm not in any way doubting you, but I can't find any reference to the cam belt tensioning only being done once in the BofH. Where did that information come from (I'm just curious)?

My BofH doesn't say anything about re-tensioning at TDC on cylinder #1 either; I was wondering about that, if one wound the engine by hand forwards to TDC then there might be a little more tension in the non-adjuster side, and so more slack on the adjuster side (depending on exactly where the engine was on the stroke of course, a degree or two past TDC would create the converse situation). I'd have thought it would have been better to re-tension at the 90/270 degree point where the engine would tend to stop anyway and by definition the rotational forces would be least (which is why it stops there) and so the tension on the belt would be lowest. Just my thoughts; I can't find that written down anywhere - and can't help thinking the BofH would have mentioned it if it made a difference.

Best wishes,

Alan

[Laird Scooby]

Originally Posted by Othen

Good morn Dave,

Many thanks for this - Chris and his son have a really interesting project here.

I'm not in any way doubting you, but I can't find any reference to the cam belt tensioning only being done once in the BofH. Where did that information come from (I'm just curious)?

My BofH doesn't say anything about re-tensioning at TDC on cylinder #1 either; I was wondering about that, if one wound the engine by hand forwards to TDC then there might be a little more tension in the non-adjuster side, and so more slack on the adjuster side (depending on exactly where the engine was on the stroke of course, a degree or two past TDC would create the converse situation). I'd have thought it would have been better to re-tension at the 90/270 degree point where the engine would tend to stop anyway and by definition the rotational forces would be least (which is why it stops there) and so the tension on the belt would be lowest. Just my thoughts; I can't find that written down anywhere - and can't help thinking the BofH would have mentioned it if it made a difference.

Best wishes,

Alan

The information originally would have come from Volvo and then Haynes printed it :


Overview of the double-page spread ^^^^^


Close-up of paras #15 & #16, with the specific instructions on retensioning.

Engines, particularly 4-cylinder engines, tend to stop with "two up, two down" on the pistons so one or other of the pistons will likely be at TDC on a firing cycle. It's unusual that they stop with all 4 pistons at the same height which would be 90 deg B/ATDC depending which you looked at.

The way the camshaft is arranged (remember it turns at half crank speed) is such that the lowest amount of tension on the slack side of the belt (where the tensioner is) occurs at this point (TDC #1) in the firing cycle. Hence tensioning/retensioning at this point, regardless of where the engine was when it stopped.

[Stephen Edwin]

David.

You appear to be referencing pages 38 and 39 (?) of which Haynes Manual?

Thank you.


Edit. Fig 1.8 for example looks of some interest.

And I am interested to obtain perhaps one of that edition of Haynes to read the pagesfully in full context.






.

[Laird Scooby]

Not that it makes any difference as it still covers the B230 but it's the 740/760 Haynes Owners Workshop Manual - not one of the Mickey Mouse "Service and Repair" manuals that don't give information.

[Stephen Edwin]

Are there different edition, model years, if possibly so which have you referenced please?




Gosh loads "fit" the description. Please, one of your famous photographs, of the cover?






.

[Laird Scooby]

Originally Posted by Stephen Edwin

Are there different edition, model years, if possibly so which have you referenced please?
.

It doesn't matter, the procedure is the same for all red block OHC engines. Although the article references the B230, the stripdown and rebuild was done on a B23ET so obviously applies to all red block OHC engines.

[Stephen Edwin]

David.

I should like to purchase one of the Haynes manual that you are referencing. Which 740/760 Haynes Owners Workshop Manual is it please?

Thank you.




Edit. Also to all and everyone. It seems likely an early Haynes for 240 might have equivalent content? Does anyone know please?






.

[Othen]

Originally Posted by Laird Scooby

Not that it makes any difference as it still covers the B230 but it's the 740/760 Haynes Owners Workshop Manual - not one of the Mickey Mouse "Service and Repair" manuals that don't give information.

Ah ha! That is why I could not find it in my BofH Dave, it is for the 240/B21 motor.

In my book there are just two sentences regarding timing belt adjustment in ch1.sect.30 neither of which mentions adjustment at TDC for #1, either for initial fitment or re-tensioning at 600 miles (just one sentence on that). I was not doubting you, and thank you for looking up the details.

I think we might have to agree to disagree about engines tending to stop at TDC - in my limited experience of 4 cylinder engines in cars and bikes they almost always stop at the 90/270 degree position before the pressure in the cylinder on its compression stroke gets too high, and the pressure in the cylinder on its power stroke gets too low so they more or less balance each other. This doesn't matter a fig of course, its only manifestation is that the starter ring tends to only wear in two places - otherwise it doesn't make any difference. You may well be right and I've just got that wrong over the years.

When I re-tensioned the belt on my B21a motor I didn't particularly set the engine at TDC (I had not heard of that requirement at the time), it was a little bit quieter afterwards though, so I'm guessing the belt was either a little bit tight or loose at that point.

All is well now :-)

Alan

PS. This is all the detail the 240 BofH contains (apologies for the poor photo):

[Stephen Edwin]

David.

I really should like to buy a copy of the specific manual you are referring to. From the simple page numbering I suspect it is an early edition. The earliest edition I can find is 1982-1986. But I am shdow boxing in the dark trying to find the actual book you are referring to. Which edition of Haynes are you referring to please?




.

[loki_the_glt]

In neither of the two Haynes manuals for the Volvo 240 I have to hand (ISBN 0856962708 and ISBN 085696591X) is any mention made of the need to re-tension the belt. As these are from 1977 and 1981 respectively it would suggest that Volvo discovered the need to re-tension the belt at some later stage.

The only other manual I have to hand is the Service and Repair one for the 940 (ISBN 9780857336514, copyright 2007) which instructs the owner/servicer to re-tension the belt with No.1 cylinder at TDC on the firing stroke and, where a new belt has been fitted, to repeat this after 600 miles.

I shall haveto dig out my other 240 manual and the 700-series one and see what they say about the matter.

If Othen or Chris is working from an early manual then that would account for their being unaware of the specifics around the (re-)tensioning of the belt.

Stephen Edwin may now be able to track down the Haynes manuals that he needs by checking the above ISBNs.