Power loss

Hi, I have a 1974 series 3 petrol, I've noticed when I change from 3rd to 4th gear the power just dips and it takes a while to build up almost like going from 3rd to 5th on a 5speed box, anybody have any idea what might cause this or is it just par for the course on series 3's? Thanks

Yes and no. If it's a noticeable recent problem it could point to an underlying engine compression issue. Is the cylinder head converted for unleaded? No, it is how an S3 std petrol engine will accelerate but depends on driving conditions.

My 1974 series 3 accelerates smoothly and evenly through all forward gears.....its not a sports car so to a modern car it will feel a little sluggish.....and mine has been completley rebuilt.....Chris

sounds like the ratios from 3rd to fourth is a big jump, but if its a standard series box then it sounds like the engine maybe a bit tired, as it would struggle to get up to speed, do you have a overdrive fitted, cause i think if you had a overdrive fitted and had it in she would probably do that as the revs would drop right down to around 1200-1600 rpm?

Tony.

kommer2013 said:

sounds like the ratios from 3rd to fourth is a big jump, but if its a standard series box then it sounds like the engine maybe a bit tired, as it would struggle to get up to speed, do you have a overdrive fitted, cause i think if you had a overdrive fitted and had it in she would probably do that as the revs would drop right down to around 1200-1600 rpm?

Tony.

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Thanks tony, yeah its fitted with an overdrive which in fairness drops revs back its not a major thing just wanted to get a bit of feedback from other owners, she is running well in general

chris7 said:

My 1974 series 3 accelerates smoothly and evenly through all forward gears.....its not a sports car so to a modern car it will feel a little sluggish.....and mine has been completley rebuilt.....Chris

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Thanks Chris, your right there certainly no sports car! Might look into it a bit further unlike yours it's a little inconsistent through the gears

John S said:

Yes and no. If it's a noticeable recent problem it could point to an underlying engine compression issue. Is the cylinder head converted for unleaded? No, it is how an S3 std petrol engine will accelerate but depends on driving conditions.

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Good question I doubt it has been converted, the previous owner gave me some lead substitute with it which in probably not using enough of.....

i have to use a upper cylinder lube for my valves but i dont bother as the valves are worn out, well all my valve gear is worn out, and i will be getting new valve gear some time. but it runs quite fine without the lube, but depends, i have heard a few years ago that it is sometimes not necessary to run lube as a bloke said that you wont get much valve seat recession, and it could take many years for the seats to wear out anyway.

an old german man that lived across the road from me said, 'all those additives on the market are just marketing gimmicks trying to con people by saying it will fix this and that' i sought of think the same, the only way to see if any additive would work is do a proper long term test and see if the product works, cause the manufacturers claim this and that but in todays society there are a lot of misleading companies out there that just want to make money by claiming it works.

Tony.

Then that is highly likely to be the problem. Additives will help but not an absolute solution. A refurbished cylinder head done by Turner Engineering will cost £300-400. You have to send the original and they re-work that. There are other good motor engineers who can do this too. It will transform your engine and set it up for years to come. I recommend considering it. If you can't remove the cylinder head yourself a good independent old style garage will do this and you or they arranged to courier the head to whoever is doing the work. Overall timescales maximum 2 weeks.

i can get my head done with new valve seats for around $350, so it is cheap john, any automotive engineer should be able to do it.