PRODUCT FITTING INSTRUCTIONS
CAM TIMING 308
CAM TIMING 308
CAM TIMING & VALVE LASH
Cam type : '308' long circuit race cam
LCA : 101.0 deg
Time cam in at : Generally, start at split overlap at cylinder no. 1 valves,
or - 101 deg ATDC at no.1 inlet valve
or - 98 deg ATDC at no.1 inlet push rod
Recent dyno testing has shown that in the majority of large-bore race engines, best performance is given at 98 deg ATDC at the inlet valve (96 deg ATDC at the push rod).
Valve Lash (Clearance): 0.028” - re-set to this once engine is HOT.
The above are purely best starting points. Ultimately the only way to extract the best performance envelope from an engine build is to dyno it and advance or retard the cam timing to achieve just that. The multitude of factors/components that go in to each engine build will likely require different cam timing one to the next. Having said that, the vast majority of engines I have built and dynoed have produced best torque/power with the cam timed in at 97 to 98 degrees ATDC at no.1 inlet valve with compression ratios in the 11.8 to 12.2 region. Higher CR is likely to need less advance, lower CR likely to need more.
It is always preferable to time the cam in on 'split over-lap' as this negates minor manufacturing discrepancies and generally gives the best performance envelope. For further information on camshaft timing and methods on how to do it with or without certain 'professional' equipment please see the information on my web site in Calver's Corner, Camshafts, at -
Research and experience indicates that most cams that wear out prematurely start to fail during the first few minutes of operation. Many cams are irreparably damaged, even before the engine is started, because the basic rules of camshaft installation and break-in have not been followed.
The cause of premature cam and follower failure is metal to metal contact between these two components. Should this contact occur due to lack of proper lubrication or excessively high pressure due to valve train interference shearing the oil film, then 'galling' will take place. When this happens metal is transferred from the follower to the cam or/and vice versa in a process comparable to micro-welding. Microscopic high spots, present on all machined parts, become severely over-heated due to friction and pressure so bond together, tearing sections loose from follower or lobe. These pieces of metal remain attached and create further over-heating during the following rotations of the camshaft. Ultimately leading to failure of the affected components.
The cam is supplied with a new cam gear key and oil gallery end plug. Typically these are not fitted, but supplied in the cam bag. Make sure the oil gallery end plug is fitted after washing/blowing out the oil gallery. Fit using a thread lock compound.
VERY IMPORTANT NOTICE:
It is absolutely essential that the oil pump fit is checked prior to final assembly. Various non-genuine oil pumps on the market have been found to have a longer drive spindle that can bottom out on the drive slot in the end of the cam. The consequence is locking up of the camshaft so it does not freely rotate. The result of not checking the fit/cam end float could be very rapid wear of the oil pump and all the disastrous damage that can cause. Fit the cam in to the block, fit the engine front plate with gasket and cam retaining plate, then fit the oil pump with it's gasket. Check the cam rotates freely and there is a noticeable end float by puling/pushing on the cam drive end.
Note: Use lube supplied smeared on LOBES only. Lightly oil cam follower walls with ordinary engine oil only when fitting in to block. The followers must be able to spin immediately at start up. It is also absolutely essential that a suitable engine oil is used. Many modern oils do not have sufficient protective phosphates in them for old style push-rod engines. Make sure the oil you are going to use is suitable for this type of engine. I use and recommend Torco. Castrol R40 vegetable based oil is still very good but must never be mixed with mineral based oils, including the cam lube supplied with this cam. Otherwise a good quality (mineral semi or fully synthetic) can be used providing a quality additive package is mixed in to it. I recommend Torco ZEP or ZDDPlus.