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3.9 V8 camshaft / misfire questions


SteveRK
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Two questions for those in the know about camshafts, timing and options:

Would a 3.5 EFi camshaft work o.k. in a 3.9? reason for asking is that that having done some visual checks on No.1 cylinder exhaust valve timing it appears that the valve 'duration is a lot less that the std' 285 degrees. I replaced the camshaft & chain a while back (non genuine cam') but never bothered comparing it with the original worn out cam' before fitting and wondered if I had been given the wrong camshaft???

secondly, if a friend was to have installed a new camshaft and chain on my, oops sorry 'there' engine but stupidly didn't quite get it correct to the tune of 1 tooth retarded cam' timing would the engine still run o.k. albeit with a rough idle and surging at low speed/light throttle?????

thanks

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Replaced the camshaft, tappets, push rods & chain about 1000 miles ago so i suspect the cam is still o.k. although having checked the receipts it appears to be an Allmakes cam' :(

Looking at Rover spec's for camshaft valve timing there is a lot of variance in the opening and closing angles depending on whether its carbs', 3.5 injection or 3.9 injection. I'm suspecting I have a 3.5 injection cam' and its always run slightly iffy since changing the camshaft, but was running iffy before (orignal camshaft & tappets utterly knackered)

Next stage is to re-check valve timing on No.1 cylinder and if not as it should be remove the front section to investigate re-timing the camshaft :(

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Hi,

Was the new cam fitted with plenty of cam lube and bedded in as per the manual instructions? If not you can scrap a new cam and followers no matter what the make in not very many miles! Ask me how I know :rolleyes:

As FF says fitting a 3.9 cam to a 3.5 is a common "performance" upgrade so I wouldn't get too obsessed with measuring opening angles, durations and overlaps. Also the rover V8 will stand a lot of abuse, mine had some lobes that were almost round before it started to mis-behave in normal driving. So as you say it was running "a bit iffy" before the cam change maybe your problem lies elsewhere?

Mike

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Hi Mike

yes i did the normal run in process but on inspection recently after taking the engine out for other reasons some of the tappets are showing signs of non-rotation, a future problem in the making but its a very little used RR so i'm not too concerned,,,,, at the moment.

The 3.9 cam angles are very similar to 3.5 carb' but not the 3.5 injection. This could imply that they got it wrong on the 3.5 injection and reverted back to the 3.5 carb' version.

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