O Series Timing Belt

[Ricky]

Hi all,

Just a quick question regarding the timing belt on the O series - what is the correct tension on it, because mine seems to move more than I would like! When I say move more, I can push it in a good inch at the bottom of the front run, and easily turn it through 90 degrees.....!
Also, is there supposed to be a cover down there, I can't see a logical home for one but I would have thought it would have one!

Thanks,

Ricky.

[G Force]

Hi Ricky. I would say that the timing belt is too slack on your monty. There was a special tool and a strain gauge for setting the belt tension, but I always turn the engine two turns by hand d.o.r and for a new belt around 1/2 inch deflection mid run at the front with moderate force, you could expect slightly more on a used belt, but you should not be able to twist through 90 degrees like on yours. There is no bottom cover on the O2 series engine. :)

[mgdavid]

IIRC one of the manuals states you should *only just* be able to twist it through 90 degress at the mid-point of the run towards the front of the engine...

[Beaker]

The instructions in the haynes manual for the TD says 45 degrees. Not sure if that is the same for all O series.

[skipweasel]

IIRC one of the manuals states you should *only just* be able to twist it through 90 degress at the mid-point of the run towards the front of the engine...
Trouble is - that's so dependent on how strong your fingers are. I did a friend's Astra once which had much the same comment - so I did what it said and it was way too tight. You could hear it thrumming when I started up - so I slackened it off a bit and all was well.

[B18 GPC]

When i do any belts , i make sure i can move it about 1/4 an inch .. or twist just .. run it up and check again .. then give a test ..

[Beaker]

When i do any belts , i make sure i can move it about 1/4 an inch .. or twist just .. run it up and check again .. then give a test ..

I wouldn't advise running anything until you are certain it is at the correct tension. Only turn over by hand.

[B18 GPC]

I wouldn't advise running anything until you are certain it is at the correct tension. Only turn over by hand.


That too .. on the bottom pulley normally .. go in through the wheel arch id guess

[weasel2400]

A rough idea for most cars is to be able to twist about 45% without being goef capes but 90 sounds dangerously loose to me :worried:

[Ricky]

Yeah, that's pretty much as I thought, it is a shame because the belt itself looks quite good, but I suppose you can never tell..... Better get it sorted now rather than have a hefty repair bill when it does snap! Seems to be the hour of the timing gear malady, as the LX has just decided to exhibit a bit of chain rattle occasionally under load...... :banghead:

Thanks for the advice,

Ricky.

[aerosam99]

Tighten the belt till you can twist through 90 degrees, turn the bottom pulley round twice so that the cam rotates all the way to TDC again, check your timing marks all still align and re-check the tension. Adjust as necessary and repeat the process till all is well.

As someone else said, don't try to start it till your 100% sure everything is set up correctly.

[e692wtt]

As an aside, the O-series is an 'unsafe' engine - if the cambelt snaps then pistons will meet any open valves and the engine will be damaged. Pistons can also meet open valves if the valve timing slips (usually due to a loose cambelt).

But the S-series is a 'safe' engine - they usually survive a snapped cambelt or slipped timing unscathed.

A-series and R-series have timing chains and so don't have 'snapping or loose cambelt' problems, but whether they are 'safe' or not if the timing chain snaps (very rare, admittedly) I do not know.

[weasel2400]

I assume the perkins prima Diesel is unsafe ?? correct me if I'm wrong, the safest car I know is the Volvo 240/440 - they never seem to get damaged.

[E_T_V]

The TD is very unsafe :D There is virtually no clearance between the valves and the pistons

[weasel2400]

Im glad I have a spare engine then, which I have changed the cam belt on - I havent done the one in the car but then if that snaps it would just force me to get my arse in gear and swap them over :D .

[tony]

I assume the perkins prima Diesel is unsafe ?? correct me if I'm wrong, the safest car I know is the Volvo 240/440 - they never seem to get damaged.
and the 760 too , is it the same engine? , i had one snap on a 760 i had :giveup:

[weasel2400]

I'm not sure but I would think its the same design at any rate, I love M & M's (including the chocolate variety :laugh: ) but volvo's are high on my list behind them, my only grip with the more modern ones is the perminant lights that are always on from ignition,two reasons 1) if you have a dodgy battery/alternator/wireing your dead before it's even tried to start, 2) having your lights on with the sun out althogh not in the highway code is the old army term that most people still recognise for carrying a heavy load, like another engine ;) :

[F690OTF(RIP)]

having your lights on with the sun out althogh not in the highway code is the old army term that most people still recognise for carrying a heavy load, like another engine ;) :

Well, you learn something new every day. It's a good idea, that.

[weasel2400]

It's the same thing as flashing your lights too give way (or to say thankyou for that matter)

in the highway code it's just to warn that you are there but anyone who has ever been or is a relative of someone who was in the armed forces recognises it as giving way in favour of the other vehicle aproching.

[skipweasel]

2) having your lights on with the sun out althogh not in the highway code is the old army term that most people still recognise for carrying a heavy load, like another engine ;) :I've always read it as "In convoy". Well, obviously only when there's several cars in a row doing it.

[H48HPE]

I've always read it as "In convoy". Well, obviously only when there's several cars in a row doing it.

My dad (who was in the army) also told me that it meant 'in convoy'. could also mean other stuff too i supose,

andy

[BIGLAD]

I assume the perkins prima Diesel is unsafe ?? correct me if I'm wrong, the safest car I know is the Volvo 240/440 - they never seem to get damaged.

Yes, The Prima engine is unsafe and as ETV says the clearance is very close.
If the valves and pistons touch (at much above idle speed) due to cambelt failure, the cam usually snaps in 3 places :giveup: :eek:
It pays to get the cambelt changed if you are unsure of the history of it.

[Insurance_shafted]

and the 760 too , is it the same engine? , i had one snap on a 760 i had :giveup:

Don't know if the Volvo 760 has the same engines as the 240/440 - these have a range of engines in anycase. I think there are/were about four engine types between 1.6 and 2.0 litre that go into the 240/440. Weasel is quite right though, re their 'safeness' when the cam snaps. Friend of mine had it happen a year or so ago in a 1.8l 440. Cam was replaced and ran okay afterwards.

Though rubber cams are naturally more prone to snapping than chains, timing chains can break also. I was reading in CarMechanics about this having happened to a Volkswagen Sharon V6 that had only done around 100,000 miles. This is the same lump found in the VW Golf though I think it's referred to as the VR6. Problem with this is that the whole engine and gearbox have to come out because the belt is positioned at the gearbox end of the engine!

Re the use of headlights when the sun is shining, I lived in the States for a few years and I believe the use of headlights is compulsory in the state of Arizona where the sun shines just about all the time - even at night...well. if you have had a few tequilas! :D

[e692wtt]

... Though rubber cams are naturally more prone to snapping than chains, timing chains can break also. I was reading in CarMechanics about this having happened to a Volkswagen Sharon V6 that had only done around 100,000 miles. This is the same lump found in the VW Golf though I think it's referred to as the VR6. Problem with this is that the whole engine and gearbox have to come out because the belt is positioned at the gearbox end of the engine! ...

The car in question was a Ford Galaxy 2.8, and yes it is the VW VR6 engine. Reading between the lines, it seems that 90,000 miles is a 'reasonable' life expectancy for the timing chains in these engines. You may get more, or the chain (actually, there are two and I think it is the upper chain that 'lets go', but that's not important...) may fail causing the engine to grenade itself...

I also seem to recall that some Nissans have trouble with their cam chains if oil changes are neglected, leading to the engine doing an 'exit stage left' :laugh: when the cam chain fails.

I reckon there's nothing wrong with cam belts, provided they are treated as a service item, checked for oil contamination regularly (when you check your underbonnet fluid levels) and replaced as directed in the service schedule (or as soon as possible if oil contaminated, with the oil leak(s) fixed at the same time.

Oil leaks onto the cambelt are usually due to blocked crankcase breathers on the earlier S- and O-series engines with the more-exposed oil filler pipes and breather 'traps', but the later engines suffer to some extent too I believe, so I make a point of checking my Monty's breather system when I check the underbonnet fluid levels (along with the cambelt). When the crankcase breathers are blocked, the engine can't 'breathe' the fumes out, so they build up and eventually leak out through oil seals when their pressure is great enough - straight onto the cambelt, and sometimes the clutch too, among othe less important bits of the engine, and the car's underside...