BS engine specifications

[412usa]

I have been asked the following by my engine builder and I don't know the answers. Can anyone help?

Rocker ratio.
Duration and lift on a 40:80:8040 cam.
Valve lift
Spring pressures on the seat and on the head.

Any help would be appreciated. I can't find this info in the manual but I might be misunderstanding the terms.
Peter

[Geoff Dowdle]

Peter,
I assume you need this information for a Arnolt Engine , BS1 Mk11 .

The cam fitted to that engine is a N340590
Its valve timing set at .002 cold (running hot at .009) is 32 , 72 , 72, 32
not the 40 , 80, 80 , 40 as sometimes stated .
Centre line is 110 deg

The way to check the cam is timed in relationship to the crank is by setting the No1 inlet valve clearance at 0.044 inch and check that the inlet valve opens at 10 BTDC .
There is a full valve timing diagram in the BS & C,D & D2 manuals .
I often have to re cut the cam sprocket keyway up to 7 degs to get the timing correct especially on B2 engines

Cam lift is approx .211
Rocker ratio is approx 1.5 to 1
Valve Lift is therefore 0.3165
less clearance cold .002
Effective valve lift 0.3145

Outer spring pressure at 1.028 is 54lb +/- 4lb
Inner spring pressure at 1.028 is 47.5lb +/- 4lb
Combined pressure at 1.028 is 101.5 +/-

I usually try to shim the original valve springs to achieve
Assembled height (Valve Closed) of 1.240in is 70lb + or - 4lbs
Assembled height (Valve opened) of 0.925 is 125lb + or - 4 lbs
but make sure you have between .050 & .080 spring travel left (when the valve is fully opened ) before the springs become coil bound

If your valves & valve seats have been faced a few times the shims required will be over 0.100 inch and the valve spring seat will lose its location around the valve guide. I have had slightly longer & stronger springs made to to compensate for this , to keep the pressures correct .
Depending on the use of the engine I shim these springs to acheive 80lb and about 150 lb .

I hope this is of some help
Regards
Geoff Dowdle

[412usa]

Geoff,
That's great information. Can you clarify on the cam timing as the Arnolt Manual states that the cam timing is 40:80:80:40 and the timing diagram states the same.
Peter

[Geoff Dowdle]

Peter,
I have a Arnolt Manual and have found a reference to the valve timing at 40- 80 -80-40 in section 1 page 8 .
Where is the Valve Timing diagram ??

I suggest you get the engine builder to set up the cam at a centre line of 110 deg and see what the valve timing is at .002 and .009 clearance . This should clarify the timing , there should be a part number on the cam .

Geoff
can you email me a copy
geoff.dowdle@gmail.com