Head and cam ID...

[Midlife]

I am trying to work out what I have cylinder head wise. I am supposed to have a big valve 130S 1974 +2. I know it?s had a rebuild +30 thou but (yes the but) I have a distributor 23D4 40953 which lead me to the head which has no marking, meaning a head from pre 68... Then looking at the cams, it has a C type on the exhaust (one groove), but no groove on the inlet? is this right shouldn?t they both have a groove...

The engine runs really well, pulls clean on the cam from 3800 to 6000 no problems, and Im running dellortoes which are set up for the big valve(?) Any help on this would be appreciated... cheers Doug. (photo attached).

[ppnelan]

Sounds like it's made up from a collection of leftovers...

The 40953 distributor (NLA) was for Stromberg engines.

I think the camshafts should both be the same - perhaps they are and one of them has been reprofiled to match the other? Do they have the same lift?

Then again, 'if it ain't broke don't fix it' springs to mind...

Matthew

[rgh0]

You appear to have a bunch of bits assembled into a new engine. This could be good or bad. If the person doing it knew what they where doing and reprofiled the cam, rebuilt the head and reset the distributor curve you could have an engine as good or better than the cars original spec big valve engine. Alternatively it could be much worse if they just slapped the bits together with no thought or modification to get them to run properly. Given the egine runs well its sounds like they took some care at least to do it sufficently well that it runs OK.

If interested you could to do some more investigation to understand exactly what you have and whether its been done well or not. Alternatively if it runs well just leave it for the time being until you need to do work on it and then find out what you have.

cheers
Rohan

[Midlife]

Thanks for the reply, I was thinking it was a hotch potch? I recently tested the car at an oval circuit to check my baffled sump clockwise (which works ok!!). The engines quiet/smooth, sounds great and you can hear the cam come on, can?t really complain here. There?s not much past 6k so I don?t think it?s a big valve, and she does feel a bit down on power.

I am interested in digging a bit deeper, especially before I take it to a dyno. I think I need to pop the rocker cover off and check the valve lifts... would someone be able to confirm the valve lifts? So I can work out what I have.

Cheers

Doug

[elansprint]

Doug if it is a big valve head the letter N is marked on the boss in the spark plug well. This does not mean someone has notr fitted big valves to an earlier head bot the cams sound suspect
Ian

[iain.hamlton]

Doug,

Even if the components of your engine started off as something else, they may have been upgraded to Sprint/130 spec or even beyond. You can take some measurements without taking the engine apart.

1/ cams: the Sprint/130 engine originally had d-type cams. These have two grooves. If your cams have been reprofiled, the base-circle will be smaller than standard as metal will have been ground off here. You can measure this with a micrometer across the cams (the smallest dimension). Similarly, you can work ot the lift by measuring the biggest dimension and taking off the base-circle. Sorry I dont have the numbers...

Base-circle and lift of D-type cams anyone?

To go to the next stage, you can measure duration with a dial gauge and degree wheel....

2/ head. An original big-valve head for webers/dellortos has a "N" stamped ahead of plug 1. But I believe any head can be upgraded. The work involves very slightly bigger valves, some porting and most importantly, a higher compression ratio. If your engine is in excellent condition, you can get an idea of the compression ratio from a compression test.

3/ distributor. The distributor you have started life as one for a stromberg engine, but again may have been modified. The only difference between is the advance curve. The weber one (fitted to all weber engines) reaches peak advance at about 2500 crankshaft RPM, the stromberg type continues to advance to much higher revs. You can easily find out which it is with a timing light and a few minutes tinkering.... I'll bet a weber engine would go fine with the stromberg distributor - but not the other way round.

good luck, best regards, iain

[rgh0]

D type (super SE, later stromberg and big valve sprint) cams

2 grooves in hub boss if original
base circle 1.16 or 1.15 inch I have seen both quoted
gross lift 0.36 lift
timing seat to seat 26 / 66


for completeness the other original cam specs

B type (standard)

no grooves
base circle 1.20 inch
gross lift 0.35 inch
timing seat to seat 22 / 62



C type cam (SE and early stromberg )

1 groove
base circle 1.20 inch
gross lift 0.35 inch
timing seat to seat 26 / 66


The ramp acceleration curves were also increased on the C versus the B and D versus the C type cams and while the fatter profile of the cams can be observed this is hard to measure without proper cam profiling equipment.


cheers
Rohan

[iain.hamlton]

Thanks, Rohan.

Doug, I'd be inclined to check one more thing. Have a look at the jets, and venturis and check them against the book. It is easy to do with no dismantling. Again, the settings on the big valve are unique.

best regards, iain

[Midlife]

Thank you all for the feedback! very helpful... and I have gone and ordered a dial gauge/mag stand and timing disc, so I will busy next week.

I checked compression which was 160psi on all four pots, indicating 9.5:1 (standard), I thought a BV was about 170psi plus?. The dellortoe carbs are spot on to the book....

- Chokes 33mm
- Main Jet 120 (running 130s for K&Ns though)
- Main Jet Emulsion Tube 7772.5
- Main Jet Air Correction 130
- Idle Jet 50
- Idle Jet Holder 7850.2
- Pump jets 45

So I will do some checks on the cams and see what I get. Cheers, Doug.

[chrishewett]

I have just looked at my head. It should be a big valve. Does this look like an N ? It's not very clear.
I will have the cover off on saturday to check the cams.
Chris

[Midlife]

I would say that's an N, interestingly your head is painted with an alloy(?) paint as well. In your case I think its masking part of the N. Rgds Doug.