Cam belt tensioner issues

Road-race engines and ancillaries - general discussion
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hudsonhenry
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Cam belt tensioner issues

Post by hudsonhenry »

Guy

Finally putting my engine back together and I have come up against one final challenge. The engine uses Fiat FIRE 1368 pistons in a 1242 block and needed to have a reasonable amount removed from both the head and the block to get the right CR. The net result is that the timing belt adjustment now goes beyond the range of the standard cam belt tensioner. As I see it there are a few options to get the right tension on the belt but I'm not sure which is best/possible

1) source a new belt with the same pitch as standard but with one or two less teeth – not sure where to start looking, have looked at the Dayco and Gates catalogues but they do not list the pitch.

2) source a bigger diameter bearing – again I'm not sure where to start looking, I have searched several on-line bearing suppliers to no avail

3) source a bigger diameter bearing from another car that can be modified to fit – again I'm not sure where to start looking, possibly at a scrap yard where I can see lots of engines and measure up the options.

4) have a sleeve made up to fit onto the standard bearing to increase the diameter – I'm confident that I can get it made to the correct tolerances and by freezing the bearing and warming up the sleeve a little, get a good tight fit but do you think this will be safe/viable?

The last option is probably the easiest for me to sort but easy is not often the best! any help or advice you can offer would be much appreciated.

Below is the pulley with tape wrapped around it to work out roughly how much bigger it needs to be to get the right tension. It needs to go up in diameter from 57mm to 67mm.


Image


Image
Guy Croft
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Re: Cam belt tensioner issues

Post by Guy Croft »

Sleeve the bearing with a mild steel sleeve with 0.0005-0.001" interference. This is a good solution here in part because it gives more 'wrap' on the cam pulley.

GC
Will01
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Re: Cam belt tensioner issues

Post by Will01 »

hudsonhenry wrote:Guy

Finally putting my engine back together and I have come up against one final challenge. The engine uses Fiat FIRE 1368 pistons in a 1242 block and needed to have a reasonable amount removed from both the head and the block to get the right CR. The net result is that the timing belt adjustment now goes beyond the range of the standard cam belt tensioner. As I see it there are a few options to get the right tension on the belt but I'm not sure which is best/possible

1) source a new belt with the same pitch as standard but with one or two less teeth – not sure where to start looking, have looked at the Dayco and Gates catalogues but they do not list the pitch.

2) source a bigger diameter bearing – again I'm not sure where to start looking, I have searched several on-line bearing suppliers to no avail

3) source a bigger diameter bearing from another car that can be modified to fit – again I'm not sure where to start looking, possibly at a scrap yard where I can see lots of engines and measure up the options.

4) have a sleeve made up to fit onto the standard bearing to increase the diameter – I'm confident that I can get it made to the correct tolerances and by freezing the bearing and warming up the sleeve a little, get a good tight fit but do you think this will be safe/viable?

The last option is probably the easiest for me to sort but easy is not often the best! any help or advice you can offer would be much appreciated.

Below is the pulley with tape wrapped around it to work out roughly how much bigger it needs to be to get the right tension. It needs to go up in diameter from 57mm to 67mm.


Image


Image
I thought i would do a quick search of the site and see if there was anything i could lend a hand with.
I appreciate this was posted a long time ago and this maybe resurrection an old thread that was forgotten or even sorted out, but if you do have any questions about Pitch or Profiles of belts please let me know. I specialise in Profile belt design at a well known Timing Belt supplier and am involved in much of the tooling design. A question about pitch should be quite an easy one to answer especially if you have a Part No.
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LanciaNut69
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Location: Newbury, UK

Re: Cam belt tensioner issues

Post by LanciaNut69 »

Hi Will01,

Not sure what engine you are talking about here as it's not mentioned, but if it's an 8 valve 2 litre engine, and you need 2 less teeth on the belt, you could fit a 1.8 litre Scorpion belt, which has 146 teeth rather than the standard 148. Available in 19mm and 25mm

Hope this helps.

Darren
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Will01
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Re: Cam belt tensioner issues

Post by Will01 »

LanciaNut69 wrote:Hi Will01,

Not sure what engine you are talking about here as it's not mentioned, but if it's an 8 valve 2 litre engine, and you need 2 less teeth on the belt, you could fit a 1.8 litre Scorpion belt, which has 146 teeth rather than the standard 148. Available in 19mm and 25mm

Hope this helps.

Darren
Hi Darren sorry I was trying to help out with the questions hudsonhenry had on pitch in above thread.
Will
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LanciaNut69
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Location: Newbury, UK

Re: Cam belt tensioner issues

Post by LanciaNut69 »

Oops, that will serve me right for not reading the whole thing properly! Still, there are now three potential solutions given, from Guy, you and I!

thank you

Darren
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Guy Croft
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Re: Cam belt tensioner issues

Post by Guy Croft »

the poster is a 'rare visitor' in these parts I regret to say...

G
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