Cam break-in


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By DANIEL TINDER - 15 Years Ago
Push rod rotation is listed as one of the things to watch for when starting a new engine. But, if using the highest quality components/lube/etc., and a push rod STILL doesn't rotate eventually, (aside from disassembly & part replacement) is there a quick fix that can be tried, I wonder?
By speedpro56 - 15 Years Ago
That's one of the reasons additional rake is put on the cam lobes for higher lift cams to make sure the lifters rotate. And use NEW lifters as well because of the rake on new lifters can somewhat match the cam lobes during breakin.I specify at least .002 rake on any cam I order wheather high lift or not, I'm not a gambler when it comes to breakin in cams and lifters. This is one of the areas I don't like in the y-block design and that's the lifter bore size and mushroom design.
By Ted - 15 Years Ago

Checking for adequate lifter bore to lifter clearance during assembly will help to insure that the lifter will initially rotate.  I get a number of blocks for rebuilding that have been already disassembled for awhile and as such, the lifter bores may have a light layer or buildup of rust.  Even after vatting, this is just enough to allow the lifter to be installed but causes just enough drag to keep the lifter from rotating and causing a premature camshaft failure.  Rehoning the lifter bores prior to final cleaning and cam bearing installation is the fix for this.

 

Something else to check for is pushrod interference in the head.  This will also keep the lifter from turning and promote premature wear at the camshaft lobes & lifter face.

By DANIEL TINDER - 15 Years Ago
Ted (3/15/2010) Rehoning the lifter bores prior to final cleaning and cam bearing installation is the fix for this.
If not present to examine/measure/double-check lifter-bore prep when shortblock was done (routine use of a moly type assembly lube assumed?), could the additional application of some type of super-slick special solvent type lube into the valley-side lifter bores be an effective/worthwhile form of insurance?
By PF Arcand - 15 Years Ago
Gary's observation about the Y's mushroom lifters, brings to mind that as I recall, John Mummert has described the Y lifter as being somewhat fragile. On the other hand, RB on this site has I believe built two engines with very aggressive cam lift rates, which were described in YBM. I wonder how that has worked out, from the point of wear etc. ?
By Ted - 15 Years Ago
DANIEL TINDER (3/15/2010)
If not present to examine/measure/double-check lifter-bore prep when shortblock was done (routine use of a moly type assembly lube assumed?), could the additional application of some type of super-slick special solvent type lube into the valley-side lifter bores be an effective/worthwhile form of insurance?
Tight is tight.  It’s unlikely that a ‘special’ lube is going to make that kind of issue any better in the short term.  As a general rule, I’ll not break in any engines in with synthetic oil simply due to wanting that additional friction early on in which to seat the rings.
By Ted - 15 Years Ago
PF Arcand (3/15/2010)
Gary's observation about the Y's mushroom lifters, brings to mind that as I recall, John Mummert has described the Y lifter as being somewhat fragile. On the other hand, RB on this site has I believe built two engines with very aggressive cam lift rates, which were described in YBM. I wonder how that has worked out, from the point of wear etc. ?
As Gary brings up, the rake on the lobes is important.  Most reputable cam grinders already know this but it's something worth asking about when ordering the camshaft if in doubt.  I’ve run several Isky Y cams that approach 0.600” lift without any abnormal wear issues.  The first of these I used was in 2004 and this one is still running today without any issues.  Even the EMC engine had a street cam in it with 0.595” lift for the intakes and 0.602” lift for the exhausts and was punished at the EMC competition with a series of 7400-7500 rpm pulls.  This is not counting the fifty plus dyno pulls I also put on the engine here at the shop.  This particular camshaft has a shorter than normal advertised duration when compared to the duration at 0.050” which makes for a very aggressive camshaft.  Based on the valve lash holding steady, this camshaft is not having any wear issues.  Special care in regards to the over the nose valve spring pressures as well as making sure that the whole valvetrain works freely is just one key in keeping the mushroom tappets and the camshaft wear happy.

 

One of the more prevalent problems I’ve seen to date that comes back to bite the installer of a new camshaft in a Y is when 3/8” diameter pushrods are installed.  These are more prone to having clearance problems within the heads and if these rub at all in the heads, then camshaft failure inevitably follows.  The lifter must rotate and anything that prevents this is going to push the camshaft into an early failure.