13 replies to this topic

[rsk289]

I'm fitting a set of 1.5 roller-tip rockers to my 1340 'S' engine (Swiftune cam, valve springs etc. already fitted).  When I've changed the geometry like this on other cars, particularly US V8s, I've needed to change pushrod length.  I can't find any reference to this on any of the Mini sites I've looked at, nor have I seen pushrods advertised in different lengths - is it not an issue with Mini engines?

 

Thanks

 

Roger

[ukcooper]

far as I remember there's only 2 length's 998 and 1275.

[Midas Mk1]

If needed rocker pedestal shims can be used, I had to use some on my 1380 to get the correct geometry (running the MED pushrods too)

[ACDodd]

Pushrod lengths are easily changed by adding an extension piece to the bottom of the original pushrod. It costs alot of money to modify these if you have to pay someone as it is time consuming process. I made a set of 2 piece pushrods for MLMotorsport 4 years ago and these worked very well. The trick is to dry build your actual assembly then use an adjustable pushrod to work out the length that gives you the lift you need. Its worth an extra .015" or so extra lift on a nominal .500" lift setup. The most important point to note is to reduce the unsupported length of the pushrod to increase the stiffness as well as length.
I have a dedicated jig for this, although it sees little use and no one want to pay the going rate to use it. Med used to sell tubular pushrods that you simply machined to length. This would be cheaper than paying to have yours extended.

Ac

Edited by ACDodd, 04 November 2016 - 01:26 PM.

[nicklouse]

I'm fitting a set of 1.5 roller-tip rockers to my 1340 'S' engine (Swiftune cam, valve springs etc. already fitted).  When I've changed the geometry like this on other cars, particularly US V8s, I've needed to change pushrod length.  I can't find any reference to this on any of the Mini sites I've looked at, nor have I seen pushrods advertised in different lengths - is it not an issue with Mini engines?

 

Thanks

 

Roger

you will find it covered in David Vizards big yellow book.

[rsk289]

Pushrod lengths are easily changed by adding an extension piece to the bottom of the original pushrod. It costs alot of money to modify these if you have to pay someone as it is time consuming process. I made a set of 2 piece pushrods for MLMotorsport 4 years ago and these worked very well. The trick is to dry build your actual assembly then use an adjustable pushrod to work out the length that gives you the lift you need. Its worth an extra .015" or so extra lift on a nominal .500" lift setup. The most important point to note is to reduce the unsupported length of the pushrod to increase the stiffness as well as length.
I have a dedicated jig for this, although it sees little use and no one want to pay the going rate to use it. Med used to sell tubular pushrods that you simply machined to length. This would be cheaper than paying to have yours extended.

Ac

Thanks AC, yes I've done the geometry hundreds of times for Ford V8s, but there are thousands of pushrod options available for these.  I was surprised there was so little mention of it in the Mini tuning sites.  It's not so much the power that concerns me, it's more getting the angles correct for rocker to valve stem contact, centring on the valve stem tip correctly.  Ford V8 valvesprings typically take at least 300-320lbs pressure with the valve closed, I don't know what the typical figures are for Minis.  I suspect my sets of adjustable vernier pushrods and valve spring micrometer might not be the right size for these parts...

I'll have a look in the Vizard book to see what he advises.

Roger

 

edit - I see Mr Vizard suggests that unless the engine is for serious racing, the effort involved in obtaining precise valvetrain geometry is of 'questionable benefit'... maybe it's not as critical in a Mini!

Edited by rsk289, 04 November 2016 - 01:51 PM.

[nicklouse]

I think you have your answer.

 

if you have the time and the kit do it. If not it does not make that much difference.

 

you then have the problem of what to use for new push rods. if they need a small shortening then that is not to bad as can be done.

 

anything else....

[Pigeonto]

I looked into this recently, made up an adjustable rod. Just in case any one doesn't know, MED's rods for, can't recall now, their multi valve or 7/8 port  heads are longer 5 or 6mm.

Edited by Pigeonto, 04 November 2016 - 03:00 PM.

[rsk289]

Thanks guys.  The assessment to see if there's a problem or not is easy - just a permanent marker to mark the valve stem tip, dry assemble, turn by hand for 3 or 4 revolutions.  Disassemble carefully, and check the witness marks on the valve.  Should be a bright strip in the centre of the valve stem - too far to the front of the engine, and the rods are too long.  Too near the back, they're too short.  As I said, with a small block Ford you then use an adjustable pushrod to tell what length is needed, click on an order box and you're done - not so simple with the A-series.

I'll check when I get around to fitting the rockers and report back.  Now, can I change the rockers and valve springs without pulling the head?  Got an airchuck to keep the valves up, but the rocker pedestal bolts double as head bolts, what a pain!

[nicklouse]

have changed springs without taking head off.

 

some soft rope in via spark plug hole. rotate engine to push rope against valve (rockers backed off) and then get big bloke to press down on cap.

 

only done as an emergency spring change at a hill climb.

 

rockers can be changed if you back the adjusters right off and don't take too long. feels safer of a 11 "bolt" head.

 

but if I was changing rockers and valves I would be pulling head anyway as I would be wanting to check that there is no chance of valves saying hello to the pistons.

[rsk289]

have changed springs without taking head off.

 

some soft rope in via spark plug hole. rotate engine to push rope against valve (rockers backed off) and then get big bloke to press down on cap.

 

only done as an emergency spring change at a hill climb.

 

rockers can be changed if you back the adjusters right off and don't take too long. feels safer of a 11 "bolt" head.

 

but if I was changing rockers and valves I would be pulling head anyway as I would be wanting to check that there is no chance of valves saying hello to the pistons.

 

I'm only doing springs and rockers so hopefully will be OK to leave the head on, and yes, it's an 11-stud head.

 

I use an air chuck on my compressor to keep the valves up when changing springs, usually after a new cam break-in.  Works fine on a V8, can't see why it shouldn't on a Mini.  Saves turning the motor over all the time (but I suppose there's only 4 cylinders anyway...).  I generally use a big overcentre rocker-stud mounted spring compressor, but that's not going to work on the Mini.

[carbon]

Thanks guys.  The assessment to see if there's a problem or not is easy - just a permanent marker to mark the valve stem tip, dry assemble, turn by hand for 3 or 4 revolutions.  Disassemble carefully, and check the witness marks on the valve.  Should be a bright strip in the centre of the valve stem - too far to the front of the engine, and the rods are too long.  Too near the back, they're too short.  As I said, with a small block Ford you then use an adjustable pushrod to tell what length is needed, click on an order box and you're done - not so simple with the A-series.

I'll check when I get around to fitting the rockers and report back.  Now, can I change the rockers and valve springs without pulling the head?  Got an airchuck to keep the valves up, but the rocker pedestal bolts double as head bolts, what a pain!

For non-roller rocker to valve stem angles / optimisation it's the height of the rocker shaft which may need to be adjusted first. You can then use shims if it's too low, or machine the lower face of the pedestals if too high, but I would check angles as well as where rocker end touches the valve. With 'old school' standard rockers (non-roller) the contact point is likely to be towards centre of valve stem when valve closed and towards the outer edge of valve stem when fully open.

 

I've never used roller rockers, so not sure if same applies.

[Ethel]

Could be wrong, but wasn't an old school tuning trick to fit Ford followers and rods?

[Spider]

far as I remember there's only 2 length's 998 and 1275.

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there's a 3rd one too

 

Which from memory was used in the 970 & 1071 engines.