25 replies to this topic

[72r1mini]

In order to make the best of my current set up with the 731 cam, would it be recommended to use the 1.5 forged rockers?

If this will optimize my potential I can plan for a cam swap in the future

[nicklouse]

do you have the clearance for the 1.5s? are you happy with the increased wear?

 

just get some standard pressed rockers as mentioned before.

[72r1mini]

I wouldn't be able to verify how much clearance I would have with out splitting. I have no idea how much was taken off the head or block etc.

Thanks for all the valuable info,

Its greatly appreciated

[nicklouse]

I wouldn't be able to verify how much clearance I would have with out splitting. I have no idea how much was taken off the head or block etc.

Thanks for all the valuable info,

Its greatly appreciated

and here is the crux of the issue without splitting and measuring  you are really stuck with just keeping it as it is.

[Dusky]

Surely could make something to test this.
Need a dti, and something to compress the spring/valve.

[DeadSquare]

Surely could make something to test this.
Need a dti, and something to compress the spring/valve.

 

Make a 1/4" loop in the end if a piece of fine curved wire.

 

Roll a 1/4" plasticine 'rod' and push it through the loop.

 

Squash it so that the wire grips it, and it is the right size to fit through the spark plug hole and cool it so that it is fairly firm.

 

With the piston 1/2 way up the exhaust stroke, position the plasticine under the exhaust valve and get the crank turned through a further 180 degrees.

 

Remove the plastercine and measure it.  If the plastercine doesn't come out through the plug hole, repeat with reshaped plastercine.

 

Ditto the other three cylinders.

 

 

 

PS  Using something harder than plasticine, and taking great care, valves can be "held" while changing valve springs.

[Retroman]

That's keyhole surgery DS !!

 

Not sure how practical it actually is....has anyone ever done it  ??

 

I would not want the potential for leaving a lump of placticine in combustion chamber[s]

 

A boroscope would let you see it but it would still be a guess.

 

I use an adaptor on a DTi for TDC through a plug hole

 

So thinking about it....if you get the exhaust to full lift [with a DTi on it]  some how lever the rocker down till the valve stops on the top of the block and bingo a measurement.

Check the valve spring is not fully compressed.

The difficult bit will be levering the rocker down.

[nicklouse]

mmm block to valve could be the issue not valve to piston.

[DeadSquare]

That's keyhole surgery DS !!

 

Not sure how practical it actually is....has anyone ever done it  ??

 

I would not want the potential for leaving a lump of placticine in combustion chamber[s]

 

A boroscope would let you see it but it would still be a guess.

 

I use an adaptor on a DTi for TDC through a plug hole

 

So thinking about it....if you get the exhaust to full lift [with a DTi on it]  some how lever the rocker down till the valve stops on the top of the block and bingo a measurement.

Check the valve spring is not fully compressed.

The difficult bit will be levering the rocker down.

 

I used to fit cams for motor club friends, usually a 948 in an 850 or maybe a 731 in an 1100, without worry as the increase in valve lift is only 50 thou, but one day a chap rolled up, told me about his twin Webber and shaved head etc: and asked if I'd to fit his new cam.

 

It looked lumpy, and something made me wonder, so I got out the dial gauge.

 

4 bits of bent wire and plasticine  proved to him that evening, why I wouldn't do it for him.

[62S]

If you do change the cam in situ you'll need a replacement with the same oil pump drive which will restrict the choice; should be a pin drive if an original BL ST 731.

[Cooperman]

For what you might gain, higher lift rockers are really  not worth the risk.

Higher ratio rockers may give you a bit more top-end power, but with a 731 cam you will lose some bottom-end torque. That sounds like a poor trade-off for what is a relatively mild cam in an old car for road use. If it were for timed competition it would be different, but in that case you would not be using a 731 cam.