Burton BLF14 cams; engine mods

[rgh0]

Key measurements / data to start with when exploring to setup of a twin cam head:

1. Cam centre line to valve pocket depth
2. Inlet and exhaust valve overall length.
3. Distance from cam centre line to valve tips with valves seated
4. Cam base circle diameters
5. What spring packs and retainers you are are using. If you don't know the details of the supplier and specification then need to measure these up also... more details on how to do this I can supply if needed

Accurately measuring from the cam centre line is not easy but its the only reliable reference point on a twin cam head to work from. I can post the dimension of a special tool you need (or you can search as I have posted before) to make it to do that, or you can try to do it working from the cam bearings surface in head, ,,, hard but possible.

cheers
Rohan

[RemcoB]

Hi Rohan,

Thanks! I'll take some measurements this Friday. I tried to look for your measurement tool, but I only found a picture, no further details. Could you perhaps tell me more about how to make such a tool?

Also, for fast road use the general recommendation is the QED 420. Would that be an improvement over the BLF 14 profile (280 deg, .410 lift)?

Cheers,
Remco

[rgh0]

Attached PDF file sketch of the tool and dimensions that mounts in the cam tunnel bores.

Easy enough to turn up from bar stock and then mill the flat on the centre line and drill the hole to align with the valve guide and measure down through the other with a calliper end rod. Centre line flat does not need to be perfectly on the centre line as any offset can be measured and allowed for. The reduced diameter section needed due to webs in the head casting that can interfere on some of the valve locations. The two holes needed and swapped between alignment using a cut off valve stem and depth measurement as different orientations needed for different valves because of the variations in cam bearing spacings. A friend made it for me many years ago and it has served me well since ( thanks Dave!!)

twin cam valve position tool.pdf

(449.2 KiB) Downloaded 223 times

cheers
Rohan

[rgh0]

Hi Rohan,

Also, for fast road use the general recommendation is the QED 420. Would that be an improvement over the BLF 14 profile (280 deg, .410 lift)?

Cheers,
Remco

There is a range of short duration high lift cams suitable for fast road use from various suppliers. The QED 420 appears to be the most popular and a good choice as its designed to work with standard valves and the QED Q55 valve spring pack so easy to install. I personally prefer the McCoy 0.440 lift 285 degrees seat to seat as it gives significantly more top end power especially with a very well ported head without loosing midrange torque but its more of a challenge to fit with that higher lift needing specialised spring packs and normally longer valve stems and also thinner followers. The power differences are not huge for a typical standard head and 6500 rpm rev limit with anything from a 0.410 to 0.440 lift cam of similar 280 to 285 degrees seat to seat duration. The McCoy though is brilliant if building a 7500+ rpm 1600 cc road engine or big capacity 1700cc+ 6500 rpm road engine where you can use its better breathing

cheers
Rohan

[RemcoB]

Hi Rohan,

Thank you for sending me the description of the measuring tool. I'll see if I can have one made.

We did a quick assembly with the BLF 14 cam on the exhaust side. Unless I'm completely mistaken, there is only about 2.5 missing, so that would mean I'd only need 100mm valves, which is perfectly normal for a performance cam. I don't know why my mechanic told me the valves were 5-6mm too short. I'll do some more precise measurements this week.

Cheers, Remco

[RemcoB]

Indeed, there's about 2.5 mm missing, so I could use the longer stem (99.822 mm) valves, thus gaining slightly more than 2 mm. I still have the standard exhaust valves (1.325"), although I do have the big inlet valves (1.625"). Would I gain anything from installing the 1.4" exhaust valves with the BLF14?

[rgh0]

Indeed, there's about 2.5 mm missing, so I could use the longer stem (99.822 mm) valves, thus gaining slightly more than 2 mm. I still have the standard exhaust valves (1.325"), although I do have the big inlet valves (1.625"). Would I gain anything from installing the 1.4" exhaust valves with the BLF14?

You may gain a little depending on porting and exhaust system used but exhaust valve size is not that critical. I would not change it unless really chasing the last couple of top end HP

cheers
Rohan