Cambelt tIming confusion 16vt engine

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LeoM
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Cambelt tIming confusion 16vt engine

Post by LeoM » February 16th, 2014, 11:37 pm

Hello Guy,

Hope you're well. I wonder if you could shed some light on the timing marks on my 16VT engine.
We had a conversation some months ago about my Alfa 155Q4, a car which uses all the main running gear of the Lancia Delta Evo 2.

Progress has been a little slow but, as I intend to use the car for the occasional sprint and hillclimb I decided to remove the engine and gearbox so that I could easily replace all the hoses, seals and clutch.

I am intending to use a N/A Fiat Tipo 16v inlet cam and do the balance shaft modification you sent to me, so my start point was to check the engine timing. I have a workshop manual and set the marks as suggested where the two cam pulleys and the crank pulley line up with corresponding notches.

Being curious I removed a spark plug and set the engine to TDC at which point the cam marks no longer line up with the notches on the cam cover. Do you know whether the marks are there just to ease fitment of the cambelt or is something wrong ?

These are the photos of the position of the pulleys at TDC ( My Mac has done strange things with them - I can scroll across and see the whole photo if you can't I will try to reload from a different computer).

image.jpg
Crank pulley at TDC
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image.jpg
Cam pulleys when at TDC
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Cam lobes when pulley notches are in line
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Regards

Leo
Last edited by LeoM on February 17th, 2014, 12:54 pm, edited 1 time in total.
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Guy Croft
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Re: Cambelt tIming confusion 16vt engine

Post by Guy Croft » February 17th, 2014, 11:31 am

Cannot see anything wrong there Leo.

With the cam pulley timing marks on the back of the pulleys in line with the notches of the rear (steel) belt cover and cyls 1 & 4 accurately at TDC the cams should be in this position:

cyl 1 will be on the overlap, inlet and ex valves both open, inlet opening up and ex closing
cyl 4 will be on compression - both valves shut.

If that is not the case are the pulleys mixed up?

Does this help?

G
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LeoM
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Re: Cambelt tIming confusion 16vt engine

Post by LeoM » February 17th, 2014, 1:46 pm

Thanks for your response Guy.

The Cambelt was changed before I bought the car but with the engine at TDC the marks on the back of the pulleys do not line up.
When I align the two marks to the cover the front pulley notch is in line with the first small mark on the cover BTDC not the long mark.

I was confused as I thought it shouldn't run at all.

When I put the replacement cam and new belt I will forward your guide.

Leo
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Guy Croft
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Re: Cambelt tIming confusion 16vt engine

Post by Guy Croft » February 17th, 2014, 1:48 pm

sounds like it is a tooth + out?

You need to check true TDC

It is very very easy to get the cam timing wrong - those notchy 16v belts can give the impression they are properly engaged on the crank pulley and not be - then jump a tooth during tensioning.

This was the cause of many bent valves - even from main dealers..

G
Guy Croft, owner

LeoM
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Re: Cambelt timing confusion 16vt engine

Post by LeoM » February 17th, 2014, 3:40 pm

The garage that did the belt is very well respected Alfa Romeo tuning specialist - run by the son these days. I'm now starting to doubt if it was changed at all as it had been done 12000km previously by the Alfa Dealer.... difficult to age as the belt looks good but not brand new.

So worst case is I've paid €350 for nothing or for a bad job. Might explain why the car seemed to lack performance on the drive back ! It ran ok just was a bit lacklustre - is that possible with just one tooth out ?

I have checked TDC with a DTI gauge - I will be very careful when re-assembling luckily with the engine out I can take more care.
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Guy Croft
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Re: Cambelt tIming confusion 16vt engine

Post by Guy Croft » February 18th, 2014, 4:41 pm

a tooth out is a huge amount!

G
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LeoM
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Re: Cambelt tIming confusion 16vt engine

Post by LeoM » February 19th, 2014, 12:02 pm

Guy Croft wrote:a tooth out is a huge amount!

G
Sorry i wasn't clear in my post - I meant that I would expect the car to run very badly with a tooth out but it was quite smooth just slow. Thanks for the advice I will go back to basics and then report back.

Leo
Last edited by LeoM on February 19th, 2014, 5:18 pm, edited 1 time in total.
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Guy Croft
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Re: Cambelt tIming confusion 16vt engine

Post by Guy Croft » February 19th, 2014, 2:01 pm

tooth out would throw out the cam timing by miles - so yes.

G
Guy Croft, owner

LeoM
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Re: Cambelt tIming confusion 16vt engine

Post by LeoM » February 25th, 2014, 6:14 pm

I spent part of the weekend going back to basics. Checking the timing with a DTI gauge confirmed that the timing belt had been fitted with the cams set correctly in relation to each other but at 10 degree BTDC. Here I have pistons 1 and 4 at TDC
IMG_0022_2.jpg
IMG_0022_2.jpg (783.01 KiB) Viewed 2368 times


The front pulley lines up correctly.
IMG_0023_2.jpg
IMG_0023_2.jpg (730.56 KiB) Viewed 2368 times

But - in this position (although the photo is taken at an angle) the cams are way off their corresponding marks.
IMG_0024_2.jpg
IMG_0024_2.jpg (665.54 KiB) Viewed 2368 times

My confusion ( and partly disbelief), was that the car ran reasonably well and returned nearly 30 mpg on the trip which was over 1000 miles !

I now have the engine timed correctly and also made a simple locking tool for the flywheel to make sure it doesn't happen again.
IMG_0045_2.jpg
IMG_0045_2.jpg (989.98 KiB) Viewed 2368 times

Thanks again for the advice - I've also go to add that I'm very grateful for the knowledge and advice that exists on the forum. From a few simple searches I've learnt that the existing cambelt is a OE Dayco but I'm replacing it with a Gates 5279XS and also in a related area all about the problems I could have encountered if I hadn't ordered a set of flow matched injectors. As I go on with the car rebuild hope I that I too can feedback some useful information.

Leo
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