Don Terrill’s Speed-Talk

Seeking opinions as to what caused the wear on this cam bearing...

Not my setup- a friends engine which has done less than 1000km. Cam snapped and rear cam bearing has deep groove on bottom half of shell. Inline 6 setup.

The engine was half grout filled but did not have the cam tunnel align honed.

I cannot check in person as it is not local to me, pics just sent to me.

When the cam snapped we originally suspected harmonics but upon inspection of cam bearing there may be more to it?

Opinions?

Hard to tell for sure from the pic, but looks like a factory cam re-ground with fairly hefty lobe lift. That would reduce base circle & large lobe lift probably needs strong springs. That combination might have snapped the cam core.

Geoff2 wrote: ↑Wed Jan 06, 2021 2:08 am Hard to tell for sure from the pic, but looks like a factory cam re-ground with fairly hefty lobe lift. That would reduce base circle & large lobe lift probably needs strong springs. That combination might have snapped the cam core.

Thanks for the reply- this definately should not be a re-ground cam but I will pass the info on to him and get him to inspect for this, anything is possible I suppose... The lobe is .356. Spring pressures are 120 on the seat. Im running similar with no ill effects so far but with a failure like this everything should be considered..

I believe the answer is in your opening post, and you've probably recognised it already, but the pictured bearing looks tight, possibly from block distortion of the fill. (?)
Further, did the rear of the block get hot and lock the back of the cam momentarily? The 265 I6 I'm familiar with can have a slow/low water flow issue at the rear in standard form (verified with an IR gun), which has in the past for us marked the piston skirt on #6. That issue was solved with the addition of a Davies Craig EWP150 electric water pump to the existing mechanical pump (two pumps running in series).
In your friends' case, the grout filled block could be running hotter at #5&6 (depending on water pump flow capacity), taking up the bearing clearance (if any?) and grabbing the back of the cam temporarily.
Might be something to look at? If nothing else, in our case more water flow allowed a better tune across all inline cylinders from front to back because we didn't have to bandaid the rear two.
Regards
Paul

blown265 wrote: ↑Wed Jan 06, 2021 3:13 am I believe the answer is in your opening post, and you've probably recognised it already, but the pictured bearing looks tight, possibly from block distortion of the fill. (?)
Further, did the rear of the block get hot and lock the back of the cam momentarily? The 265 I6 I'm familiar with can have a slow/low water flow issue at the rear in standard form (verified with an IR gun), which has in the past for us marked the piston skirt on #6. That issue was solved with the addition of a Davies Craig EWP150 electric water pump to the existing mechanical pump (two pumps running in series).
In your friends' case, the grout filled block could be running hotter at #5&6 (depending on water pump flow capacity), taking up the bearing clearance (if any?) and grabbing the back of the cam temporarily.
Might be something to look at? If nothing else, in our case more water flow allowed a better tune across all inline cylinders from front to back because we didn't have to bandaid the rear two.
Regards
Paul

Great points... Yes, I was worried about the possibility of distortion from half grout fill and lack of align honing, but as I didn't build the engine, I am not sure if it needed it (cannot say if it was checked or measured etc). I believe he is running a EWP150 from Davies Craig as a stand alone pump but you may be onto something with possibility of extra heat in rear 2 cylinders.

Just some further info on the specific flow path for our engine (may be different from yours), and perhaps a 'picture' of what may be adding to/causing the cam breakage (or affecting a maximum HP tune?)

The water flows into the 265 I6 block at #1, around the cylinders through to #6, up into the head via two 1/2" holes at the rear of the block, and then across the head back towards #1 and out. There are five 1/4" steam holes on the exhaust side of the block/head. If these steam holes are enlarged too much, and/or more are added on the 'cold' side, then the factory pump doesn't have the capacity to push sufficient water through all these passages, and the rear cylinders then loose flow. The water at the back stagnates, #5 & #6 overheat, and then problems arise with skirt clearance and pre-ignition.

Even in stock trim (water passages between the block and head cleaned but not enlarged) the factory 1960s designed mechanical water pump is barely adequate. We saw this with both the IR gun, as well as K type thermocouples on each spark plug- readings varied from #1 to #6. (fuel distribution can play a part here depending on the manifold type, but in our case wasn't a contributor)
Despite significant improvements in radiator, ducting, and fans, we only achieved good thermal management of this engine after upgrading the pumping side. A remote external engine oil cooler circuit helped, but the key change was the second water pump. An aftermarket high flow efficient mechanical water pump would also work, but no such animal exists for our dinosaur.

In your friends' case, depending on the cars' use, the DC EWP150 may not be enough on its own. Davies Craig suggest that pump is sufficient- in my experience it performs well when used to suppliment/support/boost the efficiency of the factory mechanical. It may be worth trying a similar setup?
Regards
Paulie

From the looks of pic 2 looks like a lot of trash came out of the oil gallery into the cam bearing. Looks like it was grinding away for some time. Almost hate to ask but, what do the rod a main bearings look like? If it was an alignment, runout, or heat issue I would think the gouging would be the width of the cam journal. From what I can tell from the pic it is not.

What did the rear journal on the cam look like ?

if there wasnt any mechanical interference, the camshaft could simply have been dropped and cracked. Cast cams can grenade if you drop them.

The first pic shows that the cam bearing appears markedly 'cocked' in the bore, judging by the discolouration, and it doesn't even seem well centred on the oil gallery

Apart from the running witness, which looks 'heavy' and ridged, there are also what look like file marks (at 6 o'clock) and other general nonsense that you wouldn't ordinarily expect

The second pic shows that the adjacent (last but one) cam bearing itself is discoloured and otherwise beat up, so misalignment with the 'failed' last bearing is at least likely

So rather than distortion from fill I'd tend towards ham fisted installation ...... and 'corrective' measures ..... on top of any other misalignment that may have been going on

If they'd been Babbitt type you might have got away with it but it looks like they're Reticular Aluminium, which is much less forgiving

JMO

Thanks for all the replies. I will see if old mate can get a few more up close pics of the various cam bearings. I did notice the marks at 6 o'clock and thought that was strange, seems like they had trouble squaring up the bearing and may have burred it (then removed said burr with file).

It is somewhat irrelevant but this was a big dollar engine.

been rebuilding engines since 1974, only had one 6 cylinder camshaft break, it was a 240Z overhead camshaft and the cylinder head was warped and stressed the camshaft as soon as the engine warmed up. From the look of your pictures, your cam tunnel is not straight. I have a round bar used as a straight edge. Use it on mains and cam journals, shows up a problem every now and then.

I have seen straight cut gears break 6 cylinder holden cams. The mark on the cam bearing looks like it is from the broken piece of cam cocked in the bore.

blown265 wrote: ↑Wed Jan 06, 2021 6:33 am The water flows into the 265 I6 block at #1, around the cylinders through to #6, up into the head via two 1/2" holes at the rear of the block, and then across the head back towards #1 and out. There are five 1/4" steam holes on the exhaust side of the block/head. If these steam holes are enlarged too much, and/or more are added on the 'cold' side, then the factory pump doesn't have the capacity to push sufficient water through all these passages, and the rear cylinders then loose flow. The water at the back stagnates, #5 & #6 overheat, and then problems arise with skirt clearance and pre-ignition.

Almost sounds like these holes needed to be graded in size with the largest at the back running down to the smallest at the front.

With 0.356" lobe lift, it sounds like this cam had a lot higher lift than stock, necessitating reducing the base circle & weakening the cam core. Candidate for the 'bang' theory I would think...