Sprint Cam Timing

[Shaun]

Just looking at the timing for the standard BL - 312132 cam, have seen a chart listing this as a 18/58 - 256 degree cam. Workshop manual states 14/50 making it a 244 degree cam. Thoughts anyone? Thanks.

[soe8m]

Maybe one is measured at the camshaft and is purely camshaft data and the value in the manual is in real life. Normally at Triumph engines you have the valveplay within the timing/duration. Valveplay does have the duration a bit shorter as the lift starts later en closing is earlier because of the play. You will set the timing at full lift so valveplay isn't an issue when setting. But it's alway's an extra confirmation that after setting the timing the valves actually open and close at the given values when having the correct valveplay.

Jeroen

[Shaun]

The 18/58 came out of the Triumphtune book, lists the same for 8 valve models also, so probably wrong. However, the workshop manual also has conflicting settings

[Shaun]

I did hear that cam timing can be out from the factory, measured TDC when I stripped the engine and it was 2 degrees out (now at the machine shop) Not yet decided whether to fit a Newman PH1 or keep the standard cam, have a vernier pulley but the workshop manual giving different values for the standard cam is not that helpful. ie max lift at 108 & 110 degrees.

[soe8m]

I did hear that cam timing can be out from the factory, measured TDC when I stripped the engine and it was 2 degrees out (now at the machine shop) Not yet decided whether to fit a Newman PH1 or keep the standard cam, have a vernier pulley but the workshop manual giving different values for the standard cam is not that helpful. ie max lift at 108 & 110 degrees.

Maximum lift is at 108. 14/50 244 degrees are the correct specs of the std. camshaft. But when measuring the opening and closing those std. specs are with the valve play included. So a wrong valveplay will not result in 14/50 but for setting at 108 degrees valveplay isn't an issue. I have never measured the cam itself, the actual lobe degrees. Some were lucky to have a factory engine that was timed correctly.. So many variables in machining.

The OHV engines have 4 fitting holes in the camshaft sprocket. One set of holes is half a tooth offset so timing those engines can be very exact and simple just using the other set of holes. You could drill another set of holes in the std. sprint sprocket to be able to choose for a full tooth or half a tooth.

Jeroen

[Shaun]

Many thanks, I will report back when I rebuild the engine.

[Sprintparts]

Don't forget as the timing chain wears/stretches it will change the cam timing.

The tensioner will take the slack out of the chain, but the chain will become longer and the long run from the cam sprocket to the crank sprocket length increases and will cause a slight advancing of the cam timing. I would be very surprised if anyone could pick 1 or 2 degrees of camshaft timing movement. Also if the cylinder head/and or block face has a lot removed you can't get accurate cam timing without using a vernier cam sprocket or redrill the OEM part.

We always set up our race engines with camshaft at full lift, (102 deg) in our case and valve open and valve closed was not looked as it is easier to find full valve open (top of cam lobe) than valve open due to valve clearance and slower ramp angle.

[soe8m]

A streched chain will retard the cam timing, same as a head skim. At a certain crankshaft degrees the camshaft hasn't reached the desired lift yet because of running 'behind' of the cranckshaft. At the moment the crankpully passes it's timingmark, the camshaft hasn't reached it's mark yet because of the streched chain.

Jeroen

[Sprintparts]

A streched chain will retard the cam timing, same as a head skim. At a certain crankshaft degrees the camshaft hasn't reached the desired lift yet because of running 'behind' of the cranckshaft. At the moment the crankpully passes it's timingmark, the camshaft hasn't reached it's mark yet because of the streched chain.

Jeroen

Absolutely, seniors moment, , a stretched chain retard the timing, not advance.