push rod legnth

[john young]

Hi ,, I am putting a 1600 type 1 back together ,, the push rods are about 1/8in longer than what was in it,, this is the only thing that is different ,, I cant adjust the valves ,, I am guessing that the rocker arm assembly needs to be shimmed ,, thanks for your help,, John

[FJCamper]

Hi John,

Yes, you can shim the rockers, but you may want to get a set of pushrods cut to length.

Are you reassembling with ratio rockers?

Tell us about the engine itself.

FJC

[Marc]

Shimming will certainly make it possible to adjust the valves, but may result in less-than-perfect geometry. If the adjusting screw passes the point of parallelism with the valvestem before the valve is half-open, it'll take shorter pushrods to cure. The object is to balance the sideforces placed on the valve - too much in one direction increases wear and friction/heat.

Things (other than pushrods & rocker shims) which affect rockerarm geometry:
Case deck
Cylinder length
Cylinder base gaskets/shims
Head gaskets
Cylinder head casting
Cylinder head seating surface machining ("flycutting")
Valve installed height (refinishing of valve seat and/or valve face increases it)
"Lash caps" added to valve stems
Camshaft base circle
Cam follower length (face to pushrod seat "cup")
Rocker stand height (early "cubical" ones are shorter)
Valve adjusting screw dimensions
Rocker dimensions/ratio - as Frank suggested, higher-ratio typically requires shorter pushrods.

...it's pretty rare that an engine is rebuilt without affecting at least a couple of these factors, but if the only thing that's different is the pushrods, perhaps you may just need to search out a set from a 1300 or pre`67 1500 - they're a bit shorter than the common 15/1600 item.

[Phil69]

Are the pushrods against the lifters (sometimes they can snag on the side of the lift bores or on the edge of the lifter it's self)?
Are the lifters against the cam? Sometimes after a rebuild the lifters can stick (very rare) in there bores.