I've used 1.5 ratio rockers on a 1293 midget engine with a Kent 266 Megadyne cam.The instructions specify a valve clearance of .016" using 1.28 rockers but how do I work out the clearances for 1.5s ?
Any ideas folks?
valve clearances using 1.5 rockers
Re: valve clearances using 1.5 rockers
1.5 times the standard setting I'd have thought. Or adjust them until they sound about right.
Some people are like Slinkies - they serve no useful purpose, but they still bring a smile to your face when you push them downstairs.
Re: valve clearances using 1.5 rockers
Thanks.With a bit of help from David Vizard's A-Series Bible,a bottle of Jacob's Creek,and some long buried algebra I think I've sussed it!For anyone who's interested here's how:
Firstly what we are actually setting is the clearance between the base of the cam follower and cam lobe base profile(I think that's what it was called !)This figure is then multiplied by the rocker ratio to give the required valve clearance.So, using the figures supplied with the cam and a bit of algebra we can work out the clearance at the cam which will be 0.16 divided by 1.28=0.125. Multiply this by a rocker ratio of 1.5 =0.1875" clearance at the valve.(This does agree with similar figures given as an example by Mr Vizard so I believe I'm on the right track.)
I've set mine at 0.18" initially and the old girl has shown an improvement though a bit of further fiddling is needed.This leads me to a further question and that is just how quiet can A-Series tappets be?:?:
Firstly what we are actually setting is the clearance between the base of the cam follower and cam lobe base profile(I think that's what it was called !)This figure is then multiplied by the rocker ratio to give the required valve clearance.So, using the figures supplied with the cam and a bit of algebra we can work out the clearance at the cam which will be 0.16 divided by 1.28=0.125. Multiply this by a rocker ratio of 1.5 =0.1875" clearance at the valve.(This does agree with similar figures given as an example by Mr Vizard so I believe I'm on the right track.)
I've set mine at 0.18" initially and the old girl has shown an improvement though a bit of further fiddling is needed.This leads me to a further question and that is just how quiet can A-Series tappets be?:?:
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OneCarefulOwner
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Re: valve clearances using 1.5 rockers
I've driven exceptionally quiet A-series cars, and exceptionally noisy ones.
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Re: valve clearances using 1.5 rockers
well,I've just adjusted them to 17 thou in a bid to quieten them up and it made not a lot of difference to the clatter!So,thought I 
,the engine is hot so if I close up the gaps between rocker tips and pushrods that should result in some peace and quiet which it did.Hooray!Only thing is the old girl is now hunting away and not very happy at all on tick over.So folks ,the question I put to you is do I start fiddling with the mixture or do I readjust again with feeler gauges and live with the noise?Your opions please.
,the engine is hot so if I close up the gaps between rocker tips and pushrods that should result in some peace and quiet which it did.Hooray!Only thing is the old girl is now hunting away and not very happy at all on tick over.So folks ,the question I put to you is do I start fiddling with the mixture or do I readjust again with feeler gauges and live with the noise?Your opions please.-
Richard Moss
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Re: valve clearances using 1.5 rockers
Live with the noise - it's an A series. Have you tried Metro A+ rockers? I put some on an old 850 Mini many moons ago and I'm sure that they were quieter as a result.
Re: valve clearances using 1.5 rockers
I'd let the engine cool and set them again before doing anything else, I'd have thought 16 thou would be the minimum on that set up, the current problem could be the valves opening before the ideal time etc.
I'd imagine that the set up could be a little grumpy at idle / low revs regardless, with the high lift rockers coupled to the 266 cam does it not make the engine a little too revvy at expense of low down power. Ok for scaring old ladies on sundays outside church but have you considered running the 266 with the standard 1.3 rockers, that way you can probably close the clearences a little for quietness and have an engine that is useable through the range. I think the 266 was meant to be a little warmer thana standard MG metro cam, which was always said to be about the best cam ever available on an A series.
For my money, I'd run the cam with standard rockers and hope to gain any extra power through the breathing via inlet / exhaust manifolds and possibly head porting, which may give you the best of both worlds.
As Richard points out, some of the later (scintered?) rockers were quieter, though I believe they had a little less lift than the pressed ones, also I have come across rockers that were simply a little tappety to the point they couldn't be silenced, but this was I think old age normally affecting just one rocker and causing noise, a sign they were past their best.
I'd imagine that the set up could be a little grumpy at idle / low revs regardless, with the high lift rockers coupled to the 266 cam does it not make the engine a little too revvy at expense of low down power. Ok for scaring old ladies on sundays outside church
but have you considered running the 266 with the standard 1.3 rockers, that way you can probably close the clearences a little for quietness and have an engine that is useable through the range. I think the 266 was meant to be a little warmer thana standard MG metro cam, which was always said to be about the best cam ever available on an A series.For my money, I'd run the cam with standard rockers and hope to gain any extra power through the breathing via inlet / exhaust manifolds and possibly head porting, which may give you the best of both worlds.
As Richard points out, some of the later (scintered?) rockers were quieter, though I believe they had a little less lift than the pressed ones, also I have come across rockers that were simply a little tappety to the point they couldn't be silenced, but this was I think old age normally affecting just one rocker and causing noise, a sign they were past their best.
Re: valve clearances using 1.5 rockers
Got to agree with the above.
Are you really getting a great deal more usable power? I hope you are, but I doubt it. I use standard rockers in a stage 3 ported head, and it goes like the clappers, with plenty of low down grunt too, and ticks over perfectly. Oh, and it's quiet too!
Cheers
Are you really getting a great deal more usable power? I hope you are, but I doubt it. I use standard rockers in a stage 3 ported head, and it goes like the clappers, with plenty of low down grunt too, and ticks over perfectly. Oh, and it's quiet too!
Cheers
Some people are like Slinkies - they serve no useful purpose, but they still bring a smile to your face when you push them downstairs.
Re: valve clearances using 1.5 rockers
Thanks folks.Food for thought.The idle and power are ok.I had a fiddle using different clearances which didn't show much improvement-always the 7&8 end being noiseiest so I left it at .018 and remind myself it's 43 year old Moggy!When the weather improves I will investigate further and do a comparison with some 1.3 rockers.
Cheers.
Cheers.