Non interference twin spark - Alfa Romeo Forum
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Non interference twin spark

Hi guys, we'll I think most of us are tired and upset with a stupid 60.000kms/3 years timing belt replacement, so I thought about the next:
I read many Porsche owners also had problems regarding the timing belt of there cars and some of them modified the engine so that it won't be an interference one.
So, has anyone done this on a twinnie?
Would it be so difficult?
We all know there would be a loss in compression and therefore power, but I guess I rather loose 5% power but have piece of mind and more money to spend elsewhere.
Talk me about this.
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Far easier to save the 2 a week and get the belts changed every 3 years surely?

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I get the thought process behind it but the Porsche owners have the issue that thier engines would be expensive to replace in the event the worst happens...second hand twinnies are 10 a penny and as Mitch above said save the 2 a week and have the money ready for a camblet..?

also,if you have the technical expertise to modify the engine to a non interference then you have the nouse to do a cambelt change, having done a few twinnies in my time I can say it not hard, easier ay than a Fiat coupe turbo where you have to undo engine mounts and jack the engine up to get to it, cam locks ae cheap and belt kits not expensive either.

certainly cheaper than having pistons pulled to be modified....

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you'll be lucky to get 100 bhp from a non-interference 2.0 twinnie. Not many ways to go about it:

- reduce the valve lift,
- use a much thicker headgasket
- change the pistons for deeper valve pockets
- shorter conrods

You will undoubtedly have to combine some of the above to get to a non-interference engine.
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Quote:
Originally Posted by Cuore_Sportivo_155 View Post
you'll be lucky to get 100 bhp from a non-interference 2.0 twinnie. Not many ways to go about it:

- reduce the valve lift,
- use a much thicker headgasket
- change the pistons for deeper valve pockets
- shorter conrods

You will undoubtedly have to combine some of the above to get to a non-interference engine.
And then when the belt eventually goes you have to replace it anyway. Sorry but this is a silly idea!
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there are pistons made to make the engine safe from belt breaks but it is not cheap i think they were about 100-120 each piston + rings

so you can achieve it but at a cost . its worth doing if your rebuilding an engine but for the price its better to replace the cam belt which is easy once you have done it a few times

when i start my new project of building a super engine i will be doing this so it is something to think about
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Quote:
Originally Posted by Cuore_Sportivo_155 View Post
you'll be lucky to get 100 bhp from a non-interference 2.0 twinnie. Not many ways to go about it:

- reduce the valve lift,
- use a much thicker headgasket
- change the pistons for deeper valve pockets
- shorter conrods

You will undoubtedly have to combine some of the above to get to a non-interference engine.
I would like to know how much material I would have to take from the pistons, the part where the valves sit and then how much power I would ooze, I guess I wouldn't loose that much.
And would be so good not to have to spend the time doing over and over the timing belt, or risking a failure, or just for the sake of mind.
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Quote:
Originally Posted by mirlock View Post
there are pistons made to make the engine safe from belt breaks but it is not cheap i think they were about 100-120 each piston + rings

so you can achieve it but at a cost . its worth doing if your rebuilding an engine but for the price its better to replace the cam belt which is easy once you have done it a few times

when i start my new project of building a super engine i will be doing this so it is something to think about
Where can we buy these?
Are they specific for the twinni?!
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Quote:
Originally Posted by Cuore_Sportivo_155 View Post
you'll be lucky to get 100 bhp from a non-interference 2.0 twinnie. Not many ways to go about it:

- reduce the valve lift,
- use a much thicker headgasket
- change the pistons for deeper valve pockets
- shorter conrods

You will undoubtedly have to combine some of the above to get to a non-interference engine.
As Cuore says - which ever way you go - you most probably loose compression - a good idea if you are doing a turbo conversion, but a lot of money and effort just to get more time from a cambelt .

Way back when smaky drove his 146 from the showroom until the cambelt broke:
http://www.alfaowner.com/Forum/alfa-...486-miles.html (Cambelt fails at last, 105486 miles)
Quote:
It was my intention to see just how far an original belt would last, the verdict, 9 years, 105486 miles
So yes you can push the boundaries if you want to, just be sure you know what you are doing, and why you are doing it.
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