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Author Topic: Cam timing woes?  (Read 4413 times)
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hongkongphooey
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« on: September 11, 2010, 07:17:16 PM »

I've just been trying to start the engine in my spyder after having it out for the resto. Needless to say,it won't start.While the engine was out,i took the head apart to clean it,lap the valves etc and i changed the timing belt. When i took the belt off,the marks didn't seem to line up very well anyway

So the first thing i looked at trying to start it was the ign timing,it seemed to be way out going by the mark on the pulley/belt cover. So i checked the cam timing holes again and they don't line up when the crank pulley mark is in line with tdc mark on the cover.Infact,the mark is about 90 degrees out when i line the cams up.So i checked 4 is at tdc when the cams line up and it is....which is odd.

Anyway,i took the cam covers off to watch the lobes as i rotate the engine,and they don't seem to be in the right place at the right time,although i can't be sure. As all the marks lined up when i refitted the belt the only way i can see them being wrong is if i've fitted the wrong pulley to the wrong cam,or even put the inlet and exhaust cams in the wrong way around...Is this possible? Can i put the cams in the wrong side or get the pulleys mixed up? It also seems to be blowing fuel back through the carbs and the engine turns more freely when i put my foot on the throttle which seems to suggest the timing is wrong.

Does anyone have a nice photo of the cam positions when all the marks are aligned and the engine is at 4 tdc? This would help immensely! Or,are there any identifying marks on the inlet/exhaust cams that i can check?

Many thanks..
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75coupe
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« Reply #1 on: September 12, 2010, 01:38:21 PM »

Hi, it is possible to put the cam pulleys on the wrong cam, but the cams themselves are identical - it does not matter which goes where - so long as they are a matching pair - which they will be if standard cams.

The beta is timed with 1&4 at TDC, with 4 on the firing stroke, so both inlet & exhaust valves closed and rotor arm pointing to 4 on the dizzy cap. Valves on no.1 will be "rocking" - inlet valve opening up and exhaust closing down.

Cam pulleys - if they are flanged type inlet will have rear flange, exhaust rear flange. may have letter "A" on inlet and "S" on exhaust.

Don't worry if you can't get holes in pulleys to align exactly with pointers - usually you will have to go slightly one side or other with one or both cams. It will depend on various factors like whether head or block has been machined, head gasket thickness etc, affecting overall height and therefore length of belt run from crank pulley to inlet cam pulley. In my experience I have only ever got the timing 100% right with adjustable pulleys. It will run OK one tooth either way - but don't go more than this - it is very easy to bend valves in this engine!


Here is a pic if it helps


* Beta cam timing marks.jpg (148.73 KB, 1367x898 - viewed 2452 times.)
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hongkongphooey
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« Reply #2 on: September 12, 2010, 04:46:33 PM »

Hi

Thanks for the reply....since posting the question,i found a photo i had taken of the pulley positions before taking it apart,and noticed the pulleys were marked with a 1 and a 3. 3 was on the inlet and 1 on the exhaust. I had them the wrong way around (god knows how,as i bagged them up!) So i've swapped them,timed it up again and now i'm getting contact after about 1 and 3/4 of a crank revolution with the no2 inlet valve on the no2 exhaust stroke. Although the pulleys are different to the ones in your pic,all mine line up except for the bottom pulley which is about 90 degrees to the left of the mark shown in your pic.Yet the engine is definitely at tdc and the mark on the actual toothed pulley behind the aux belt pulley is lined up correctly.

Are the locating dowel on the cams in different positions for the inlet and exhaust then?

Does anyone have a pic of the actual cam lobe positions when lined up correctly?

Cheers.
« Last Edit: September 12, 2010, 05:20:38 PM by hongkongphooey » Logged
hongkongphooey
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« Reply #3 on: September 12, 2010, 05:02:30 PM »

Also,my inlet and exhaust cams are visually the same,except no1 lobes are in different positions by about 120 degrees. At the moment the exhaust has just shut and the inlet is about to open,which by what you say is correct yet no2 lobe inlet seems to be slightly in the wrong place. If a swap the cams over,then no1 exhast would be coming up to opening and no1 inlet would be past shutting but with the engine in this position,no1 should be about to start its induction stroke?


Arrgghhh,this is doing my head in!
« Last Edit: September 12, 2010, 05:18:41 PM by hongkongphooey » Logged
75coupe
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« Reply #4 on: September 12, 2010, 10:07:54 PM »

Cam dowel positions should be same for both cams, it is only the pulley holes that are different. Do you have a pic of the cams in the position you describe? Will take a picture of cams in correct position later today.

No. 2 con rod can hit the fuel pump eccentric on the aux drive shaft if this is not timed properly - could this be the contact you describe?

If the timing was as far out as you described with pulleys reversed you may have already bent a valve....There is very margin for error....

Will post a pic later today
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hongkongphooey
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« Reply #5 on: September 13, 2010, 07:39:08 AM »

No. 2 con rod can hit the fuel pump eccentric on the aux drive shaft if this is not timed properly - could this be the contact you describe?

Ahh,funny you should say that.....i noticed after i'd swapped the pulleys over i'd aligned the dizzy drive pulley to the wrong tensioner bolt,so i took it all off and re-timed it all and it's not contacting now,so maybe that was it. I'd initially figured that i'd bent the valve,but i'm not using much force to turn the engine.

I'll post a pic of the cam positions,and if they look ok,i'll have a look at the compression to see if i've done anything nasty. There was definately no contact the first time i tried it when i'd put the pulleys on the wrong way around,as i turned it over by hand very carefully with the plugs out.
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75coupe
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« Reply #6 on: September 13, 2010, 08:02:26 AM »

Hopefully all is good then, with regard to your crank pulley, I have a 2 litre motor which has a TDC pointer mounted to the front seal housing, which would be about 90 degress to the left of where it is on the picture above.

Problem is these cars are so old know, who knows what bits have been fitted and from where......A lot of Fiat TC engine parts are interchangeable.


* Crank pulley markings.jpg (144.95 KB, 1577x988 - viewed 1164 times.)
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hongkongphooey
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« Reply #7 on: September 13, 2010, 09:50:28 AM »

Well mine did start life as a 1600 and has had the 2000 fitted at some point. The engine has the pointer that you describe,but the pulley in the first pic you posted. I guess it's a bit of a frankenstien's engine.
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75coupe
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« Reply #8 on: September 13, 2010, 11:40:22 AM »

Yes I too have a had  a strange brew of parts on my car, in fact it still has......all part of the fun I suppose!!!

I have below a pic of no.4 cam lobes at TDC, they should both be facing upwards as shown, with no.2 inlet valve closing, and No.1 inlet valve opening.

No.1 exhaust valve should be closing, no.3 exhaust valve just about to open.

As far as the aux drive shaft goes, I have cut the lobe off the end to prevent the timing problem you had, a sensible move if you are using an electric fuel pump as I am. Obviously if you are using the mechanical fuel pump this is not possible! The aux shaft is always the hardest to time as it spins so easily when you are trying to fit the belt!

Hope this helps......


* cams at TDC.jpg (59.27 KB, 694x447 - viewed 996 times.)

* inlet cam at TDC.jpg (24.92 KB, 448x336 - viewed 937 times.)

* exhaust cam at TDC.jpg (32.71 KB, 615x271 - viewed 981 times.)

* modified aux shaft.jpg (17.92 KB, 448x303 - viewed 943 times.)
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hongkongphooey
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« Reply #9 on: September 13, 2010, 12:59:16 PM »

That looks spot on to mine.....although i'll have to double check when i get home. That's given me the confidence to bolt it back together again now.I bet (hope) is was the aux shaft causing the contact.

Thanks
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75coupe
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« Reply #10 on: September 13, 2010, 01:19:12 PM »

Sounds like it was the aux shaft to me, glad to be of assistance, you'll soon be hearing the roar from those webers!! Wink
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