is it un-advisable to spin an engine backwards?

[ryan roopnarine]

I'm certainly not talking about spinning it over backwards with a reversed starter motor or anything like that, more along the lines of lining up torque converter bolts, adjusting valve trains, et cetera. I've heard this advice for the second time last weekend, with the explanation that in timing belt driven cars, one does not want to reverse the tension while under load. can anyone clarify or dispel the advice i received? thanks.

[Ross]

I see no harm. Done it myself coutless times with no ill effect.
EDit; Lots of good reasons given here not to do so. I'll consider myself lucky so far or to have had healthy timing gear.

[whiskychaser]

Dont think it matters. But I wouldnt line up my timing marks turning the engine backwards. Why? Think Bill R put it best when he quoted his dad:
' cos I said so'

[632 Regal]

only thing I would avoid reversing it would be in setting timing.

[Blitzkrieg Bob]

Can be very bad if your tensioner is weak.

the tiiming chain will slacken and skip a tooth or two.

[632 Regal]

now that would suck!

Can be very bad if your tensioner is weak.

the tiiming chain will slacken and skip a tooth or two.

[Dave M]

Turned my M50 backwards plenty. Can't see how one could bugger anything up turning it by hand. However, your question mentioned timing belts, not chains. There might be truth in not wanting to turn a belt backwards, but I dunno................

Dave

[bubba966]

Can be very bad if your tensioner is weak.

the tiiming chain will slacken and skip a tooth or two.

+1, big time.

Doing so on a clutch job has taken out S38's before. Will have to look up the last thread on this happening on the M5board. Poor guy took his E34 M5 in for a clutch job and blew up his engine because the timing chain jumped a tooth or two and the pistons hit the valves. The pics weren't pretty.

[bubba966]

Here you go.
http://www.m5board.com/vbulletin/e34...-disaster.html

[Bill R.]

you don't want to turn a timing belt equipped car backward or for that matter any timing chain equipped car that has a tensioner. They can jump a tooth and in the case of a chain bunch up or break a tensioner or guide rail. Sometimes it unavoidable but you want to avoid it whenever possible.

I'm certainly not talking about spinning it over backwards with a reversed starter motor or anything like that, more along the lines of lining up torque converter bolts, adjusting valve trains, et cetera. I've heard this advice for the second time last weekend, with the explanation that in timing belt driven cars, one does not want to reverse the tension while under load. can anyone clarify or dispel the advice i received? thanks.