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Rough Sounding Engine After Rebuild


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#1 minidave54

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Posted 31 July 2020 - 07:52 PM

I have a 1275 that has been re-bored to 1293 with new pistons, a re-ground crank and new shells. A new cam (mini spares Evolution001) and one of there recommended distributors to match.

There is also an uprated head with larger valves.

 

I have set the ignition timing at 16 deg BTDC the recommended way by disconnecting the vac pipe and blanking it off. The car starts and drives well until between about 2500 - 3500rpm in 4th when it sounds rough, and can only be described as sounding like a big end knock. At about 4000rpm the noise dies away. 

 

Would i be right in thinking that this is a timing issue and that i possibly need more advance due to the cam ?

If this is the case, what is the best way to work out my new timing ?

 

I will at some time once the engine is run in book a rolling road session.



#2 sonscar

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Posted 01 August 2020 - 08:38 AM

I would possibly try less timing first.If it is pinking it may cause serious damage.It could also be lean or it could be mechanical.Difficult to diagnose without being there.Be careful and good hunting.Steve..

#3 Minigman

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Posted 01 August 2020 - 09:08 AM

I’d try less adavance initially. 10 degrees at idle and go from there. Have you measured the advance at higher revs?

Edited by Minigman, 01 August 2020 - 09:08 AM.





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