Rotating engine backwards (warning!)

Alfa Romeo GTV6 Forum: Engine: Rotating engine backwards (warning!)
By Michael Harris on Unrecorded Date:

I had a bit of a close-call this weekend while changing the giubo's (flex-couplers) in the driveshaft. Even though I know better, I turned the driveshaft backwards (anti-clockwise) while removing the bolts for the giubo's. I kept on turning till I found the crank totally locked - at which point I had to strip down the front of the engine to check the cam timing. The passenger side cam had slipped several teeth, causing the pistons to hit the valves. If I had cranked the car at that particular moment, the valves would have been bent for sure!
I'm not sure if this problem is unique to those engines fitted with the thermo-mechanical timing belt tensioner ... the timing belt also seemed a bit loose which perhaps exacerbated the problem!
I was lucky that all is still well with my engine - compression test and various high-speed test runs :-) have confirmed this.

By Gerry Lehmann on Unrecorded Date:

Mike, its hard to know what to think on this issue. I have heard of several incidents exactly like yours. In a way I'm glad to hear that the belt was a bit loose. Fred DeMateo has sworn up and down a few times on the digest that this can't happen with either style factory tensioner but he does throw in the caveat of "if they are properly adjusted". My guess is that the real story is that, if they are a bit loose, it happens more easily with the new style tensioner. I guess I'll quietly go check the tension on both of mine.

By Anonymous on Unrecorded Date:

Fred is absolutely wrong about turning the engine backwards with the dry tensioner! DO NOT do it. It will relax and can allow the belt to slip on the passanger cam. The hydraulic tensioner does not have the same problem. Also, if you hear a knocking noise in your engine and it's not running great, check the cam timing. I have seen these tensioners fail in less than 30 sec running. They can fail with or without catastrophic results. They either work fine, fail and bend valves, or fail and allow the valves to contact the pistons making lots of ticking noise but not really harm anything. If the tensioner fails in any way, toss it and replace. Alfa does have a 6 month/6000 mile warranty for non-authorized shops and a 12/12 for authorized shops. The tensioner is considered disposable and therefore should not be re-used. I have however, before knowing the above have reused them 2-3 times for over 80k miles. I will not reuse them again. That said, if they work for 3-6 months they will probably work for a long, long time.

By Zamani on Unrecorded Date:

I think you are correct. Fred was wrong about turning the engine backwards. Never do it. My mechanic has always warned me about this. My car also ticks, but that's just the valve train chatter. It doesn't tick loud.

By Anonymous on Unrecorded Date:

BTW I forgot to mention that the belt may appear to be loose I believe depending on where the cams stop. It is possible for the pass cam to want to rotate inwards which may take tension off between the cams. I don't worry about in any more. I also park in a forward gear if the car can roll forward and rev it the car will roll back. I engage the gear after the car has settled where it wants to be with the parking brake on so as not to put undue force on any gears.

By Andrew on Unrecorded Date:

Like Michael, I turned the motor backwards while doing a drive shaft. The belt slipped 4 teeth. When I tried to start the car it blew the plenum off. I was lucky, but the word really needs to get out on this one.

The next time the valve covers are off, put some paint marks on the inside of the cam pulleys. Make matching marks on the machined area of the head. You'll have to lean over the engine to peek under the pulleys. If you are ever in doubt about your cams, you can check them with out pulling the covers off and wasting $40 in gaskets.
Every time I check the timing I hit these marks with the light. If you have the fancy light that fires on TDC, the marks will line up exactly. If you have the standard light, the marks on the pulleys will be a 1-4 degrees behind the head marks.

Andrew in LA

By rolandk_98 on Unrecorded Date:

would the inability to rev higher than 4000 RPM while driving (not standing in neutral) be indicative of a sliped timing belt (maybe one tooth?)

By Nicola Larini on Unrecorded Date:

That's possible. On some 4-V 164s, a slipped belt means rough idle and lower power.

Nicola Larini

By Ben on Unrecorded Date:

This may be a stupid question, but does this mean if you park your car (in gear) on a hill and it rolls backwards, you could slip the belt?

By anon on Unrecorded Date:

Im sorry all- but Nicola Larini- Are you THE NICOLA LARINI????????

By Martin on Unrecorded Date:


By Nicola Larini on Unrecorded Date:

Whata kinda questione is thata aaa? Aska my friend here, ees name isa Alessandro Nannini. But don't ta tell him, I yamma better driver then him.

By Ben on Unrecorded Date:

Thanks Martin - I won't do that again! In the past I've left my car in gear when I park on a hill, just for the little extra safety in case the handbrake is not on hard enough... bad idea I guess... but if it's left in reverse and rolls backwards a bit, will this still risk slipping the belt? I also worry about yanking the handbrake too hard...

By marcel on Unrecorded Date:

To Andrew,
you have not to put down the valvecovers for checking timing !!!The beltcovers have two round covers which you can put down,there are marks under them which have to correspond to the marks on the front of the campulleys.

By Martin on Unrecorded Date:


Parking uphill I put my transmission in reverse, and first.

By Ivor on Unrecorded Date:

Not a stupid question at all. This just happened to my GTV-6, the emergency is shot so I left it in first parked nose uphill. Upon starting it, the engine made a very ugly noise. The belt had slipped and the cams were now out of time. The mechanical detensioner had been good since I installing it a year ago. Now the valves are bent.

By Sandro ( - on Unrecorded Date:

We only had such problems with defectet belt tensioners, this is why someone should always
replace all seals, on the tensioner.

By Zamani ( - on Unrecorded Date:


I don't trust the belt covers. Mine is a little warped because somebody stepped on it when it was off. For safety's sake, use the timing marks on the heads (open the cam cover).

By Tony Lupton on Unrecorded Date:

The belt covers are fine for checking for slippage. Even a one tooth slip equates to a 3/8"/nearly 10mm difference against the pointer on the timing belt cover. Been there, done that.

Incidentally the two timing belt covers are surprising cheap to replace - they're only about AUD13 each.

By dp ( - on Unrecorded Date:

Yes, they're only $10-15US I think. I've had no problem using the little punch marks on the plate between the cam sprockets and the cam shaft, If I remember correctly, they generally point up and in towards the center of the motor and line up pretty darn close to the center of a corresponding bolt head. Also, one can paint or use a marker to create marks for future reference. But if you want to be 100% sure, yeah, remove the valve covers.

By marcel ( - on Unrecorded Date:

tony is right, one tooth off is such a difference that you even can check it when your engine has no belt covers mounted but for exact fine timing of the cams you have to go under the camcovers,but i doubt that a lot of you know how this fine settings are done ( no, you dont need the offset keys for that!!) - if somebody want to know that, just loose the parts of the cam and see how much "play" there is, this play can be used for fine settings and if there is not enough play ( what can be only if the heads were milled too much or for compression reasons)then the play can be made bigger.

By Brian H. ( - on Unrecorded Date:

Can you go into more detail on this?
I have 164s cams on my 2.5 and I am considering tweaking the cam timing slightly to get a bit more power down low...
What is this about the offset keys? Where, how?

Brian H.

By marcel ( - on Unrecorded Date:

you get them from sperry i think,but what do you want? more power at lower rpms?

By Brian H. ( - on Unrecorded Date:

Yes, maybe my cams are out of adjustment (I haven't yet double-checked)but I would like more power up to 2500rpm which is about where the power kicks in now. Sometimes it's a bit scary crossing fast into a busy street...

Brian H.

By marcel ( - on Unrecorded Date:

if you want more power under 2500rpm go for the original cams at first or better mount a 3.0, the 2.5 is not the right engine for that.Also a shorter diff would help, if not a 4.3 then a 4.1 is the longest i would recommend, another question,you have mounted s cams on a stock 2.5 ? If so your compression is far too low and thats one reason why your engine is not pulling.

By Brian H. ( - on Unrecorded Date:

It's an '85, so I think the tranny is not a prob.
Low compression may be OK as I am thinking of the future possibility of turbo/supercharging. Are the 164S cams bad with that ?

Do you think some adjustment of cam timing would help. What are the specs on those "offset keys" How many degrees ?

Molto Grazie, Brian

By Helpfull ( - on Unrecorded Date:

All you guys going on about the only way to check the cam timing is to lift the cam covers. Ive been an Alfa mechanic with a rcognised workshop for years and done literally hundreds of the damn things and we never lift the cam covers to check the timing unless the belt has slipped. Simply get a paint pen and mark a tooth on the rear of the cam sprocket and put a mark on head ( usually on the bold head directly behind the cam sprocket)so they lign up. Mark all the other pulleys etc the same way. When installing the new cam belt make sure all your marks lign up. Turn the motor over by hand several times and check. You WILL know if you are out a tooth, it will stand out like dogs balls.

By Greg Gordon on Unrecorded Date:

Yeah, thats great, so if the cam timing was off when the car comes into the shop, it's off when the car goes out.

By Rick on Unrecorded Date:

Hey Greg: I think "Helpful" made it fairly clear that if the car comes in and it's running fine, there's no real need to pull the covers for something as simple as a belt change. I've done so many with the cam covers left on that I can't count them, and that includes when I was working as an Alfa tech in Daytona. If the timing is off when a car comes into a shop, it either runs like a pig or doesn't run at all (valves & pistons had a little argument). It's just down to personal experience and preference. Whatever floats your boat. I think for those people changing their first belt, removing the cam covers is definately the way to go. If you've done it a few times, it isn't necessary.

BTW, when do you expect to be moving to the area?

Regards, Rick.

By Greg Gordon on Unrecorded Date:

Hey Rick, sure it's possible to do it that way but I just cringe at the thought. If one cam is one tooth off the car actually runs fine, it just loses about 30 horsepower. I have seen two Alfa V6s with the passenger side cam one tooth off and both times the owner did not realize there was something wrong. I actually bought one of the cars and drove it that way for a couple weeks. I guess if the mechanic test drives the car first to make sure it's running fine before the belt change it's ok, but I doubt they do that. Anyway if you are confident doing it that way then more power to you, but I am not. Regarding the big move, still looks like 6 months away, perhaps more, we are definatly coming though. See Ya :)

By LENZ ( - on Unrecorded Date:

One tooth definitaly is noticable. It won't idle as nice as it should but when you pass 2000RPM it sounds asiff nothings wrong.
I can imagine that if your an alfa mechanic and your out there to make money it's the fastest way to do it.
If it's your own car why not take of the camshields.
Aren't there any markings on the plastic belt shields underneath the round caps and the camwheel?

I once did a gtv6 wich just didn't ran like it should.
Asif it ran on 5 once and a while at idle, the marks on the cams were positioned ok but one bank had less compression then the other bank.
Something probably went wrong when marking the cams in the factory.
So i changed that cam one tooth and compression was equal to the other bank.
It ran like new.

By Nick Myles ( - on Unrecorded Date:

Hi All. I live in Australia, on the Gold Coast actually, if you watch the Indy car race from Australia today you will be looking at exactly where I live, I can smell the cars from here :) Anyway, this alternative to the hydraulic cam belt tensioner interests me, however this tooth jumping that the mechanical one suffers is a worry. So whats the verdict, yes or no on this ?


By Zamani ( - on Unrecorded Date:

Hey that's interesting. My 3.0's right bank (cyl 4,5,6) is off by 1/2 a tooth and the compression readings on it are between 182-188 and the right bank which are all properly ligned up have readings between (192-200). Not bad for an engine with 130,000 miles.

By george ( - on Unrecorded Date:

man, i was watching these indy cars move and they are fucked,they can not take a corner they are still not on par with the formula one cars ,it would be interesting to see a formula against an indy ,formula would kick its arse all over the place.

By Rick on Unrecorded Date:

Greg: Back again at last. I have to agree: there are pelenty of guys out who probably just slap the belt on and if it runs, that's the end of the story. And yes, they do still run when off by one tooth, just not real well.

What we used to do at RML in Daytona was pop off the little round plastic front covers and look at the indicating notches (just like a timing mark) on the cam pulley. With #1 at TDC the marks on the cam gears were at 10 minutes to 2 or the same distance from the 12.00 position, one to the left and one to the right. Hope that makes sense. Anyway, you could tell immediately where the cams were and if they were one tooth off it was pretty obvious. Again, just whatever floats your boat. The good (or bad) thing about removing the cam covers is that you can check that everything else is in good shape (did someone say camlobes?).

Let us know when you finally get to this parts of the world.

Regards, Rick.

By grim on Unrecorded Date:

Suggestions please!
I've just finished replacing the timing belt on my '86 GTV6. The car doesn't start. The engine doesn't crank. It sounds instead like a machine gun with a very loud tapping sound. The first thing that comes to mind is the starter is not engaging the flywheel, but I didn't mess with that part of the car.

While the belt was off I adjusted the exhaust valve to spec. replaced the water pump and retimed the cams and crank and intermediate shaft. Once the belt was on I turned the engine (Clockwise) 8-10 times without difficulty, retensioned the belt, and replaced all the covers/belts etc.

Any suggestions where to start?

By george on Unrecorded Date:

I think you might have crashed a valve into a piston id suggest that you not attempt to start the car again try and turn it one more time by hand and see if every thing aligns correctly if it doesnt align someting has gone terribly wrong.

By Keith on Unrecorded Date:

You said the engine doesnt turn? The popping noise you hear may be the starter solenoid clicking but not engaging the starter. Check your battery voltage to be sure there is enough to crank the engine and get it started. Also watch your voltmeter while you are cranking the engine over, as best I can remember it shouldnt drop to no less than about 10 volts, if it does the battery is too weak.

By argtv685 on Sunday, July 27, 2003 - 10:23 pm:

Hi... My 85 gtv6 was running poorly - no power - coulld not rev it up - so I decided to check the timing. I reviewed my CarDisc CD and it was absolutly no help. Right now I have the radiator and hoses out to access the front of the engine. I sliped the timing belt off, and set the pass and driver side cams to the timing mark my mechanic had put on the boltheads. I set the distributor cam so that the roter is pointing at #1 cylnder, and now I think I shoulod set the drive shaft on the pointer mark. How do I slack-off on the tensioner (mechanical) to enable me to replace the timing belt? Thanks for any help

By Anonymous on Monday, July 28, 2003 - 11:19 am:

Warning !!! I know this is a bit late on this thread but I have seen three instances where the belts have jumped off on the 24v motor 1)turned prop backwards trying to get couplings in - realised only once I started the car.2)rolled back in 5th and 3)cars timing was slightly out and engine kicked back a fractuon of a revolution when I turned the engine off.
I have seen a few GTV's where the timing marks on the cover are out so always check with the tappet covers off.
That machine gun sound is definitely valves on pistons.

By Graham L. Davis on Tuesday, July 29, 2003 - 01:05 pm:

read the Alfa Digest. Go to

Graham L. Davis
'91 164L
'89 Milano Verde
'89 Spider Grad
'85 Gtv6

By Brian H. on Friday, August 01, 2003 - 12:46 pm:

AR, if you have not yet found the tensioner answers you seek, check out this link:

BTW, I haven't tried this on my 2.5... but, on my 164 3.0 when I was adjusting the tensioner, out of morbid fascination, I intentionally (though very carefully) turned the engine backwards several times to try and replicate the "backwards rotation prob". -- No matter how hard I tried I could not get it to even "sort-of" skip a cog.
I strongly believe that there may be more issues involved.
( Of course I re-adjusted it while turning the correct direction before starting it up... )

Ciao, Brian H.

By Anonymous on Sunday, August 03, 2003 - 12:36 am:

If you continuosly(smoothly) turn the motor backwards it does not skip a tooth but if you are rocking the car back and forth to get your timing marks set it will occur ie contiously chainging the direction.If you do this out of morbid fascination it wont occur but try this the night before your race day !!

By Brian H. on Sunday, August 03, 2003 - 11:26 pm:

...It probably only happens when the engine is "reversed" after it's completely put back together anyway... :)

By Ross Gallichotte on Tuesday, March 02, 2004 - 02:40 pm:

Are you kidding? comparing apples and oranges aren't you?. F1 and Indy cars don't compare I wonder why? Maybe the 10 fold cost differental,2,3,4 times the horsepower differential.Different fuels etc. Remember Ferrari has over 450 people on the team again a 10 fold differential. Compared racing interesting? No,it would be boring. Sorta like Volkswagen beetle's versus GT40's? Both are great cars but with different purposes. If we had all comers come and race then it would be decided quickly the best car and then no more racing, only by creating class racing do we get the opportunity to see it at all. Can't turn a corner? You do not elaborate. Were they all going off in the corners? Recently there was a TV show(US) between an Indy car(and its driver) and a F1 car(and its driver) and then the drivers switched cars and toured the track, no winners but a great discussion of the differences and was highly entertaining?but only once!. If you were to drive either of these cars, essentially, you would be an incompetent.That's the fu...d part of life,we don't all get the same skill sets do we?. Again,I wonder why?, apples and oranges? Not good or bad just different!

By Denver Lawson on Sunday, August 01, 2004 - 09:08 pm:

Can any one get me an engineering drawing of the Alfa V6 block? I'm making a QV 4.3 litre version, and I'm trying to get this drawing from my local Alfa importer, but they don't seem to be having much luck. I need the relationship between the studs and the bore centrelines so I can finish the heads properly. And before anyone asks...yes I have measured several blocks. The problem is they're all slightly different. You can email me at as I'm not too sure how these message pages work;-)

By Steve R on Monday, August 02, 2004 - 01:25 am:

A 4.3 litre version ?! :-)

By on Monday, August 02, 2004 - 12:53 pm:

Yes. And you might be interested in what they're going in. We've taken a 75 floorpan and bulkhead, and shortened the wheelbase and put a 105 series 1750 and a 2000 body over them. We've done 2 of them.

By Greg Gordon on Monday, August 02, 2004 - 01:42 pm:

That sounds incredible. Do you have a website with pictures?

By nizam on Wednesday, August 04, 2004 - 03:07 pm:

I second that motion! We would ALL love to see your project! Sounds very inspirational!

By on Thursday, August 05, 2004 - 04:46 pm:

We tend to hide........ But if you're good I might send through some pics of the heads once we get them a bit closer. Actually, you CAN look at our website, but I'm not sure we've got pics of the Alfas on there (they're our own cars). But there's some other interesting stuff on there. So...anyone got an engineering drawing? I guess that's a no.....

By Anonymous on Monday, November 08, 2004 - 08:03 pm:

ive had the timing belt slip off while or possibly (hopefully) at the instant when the engine stopped running. (ive put the belt back on ) im reluctant to try to start it up again to see how much damage has been done. whats the best case scenario? can i do more damage now if i run it with bent valves, assuming that it will run at all? (i cant afford garage fees)

By Mottic on Monday, November 08, 2004 - 09:03 pm:

Best case scenario is you got lucky (and I hope you did) - worst case, it won't run at all. The first question I would ask, is why did the belt 'slip' off? Don't just put it back on without determining why it came off in the first place. What style tensioner do you have? Once you've verified the integrity of the belt/tensioner, you'll want to pull the cam covers and verify the timing.

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