Cam Groove in '73 CE motor w/photo - did this cause bent pushrods

[Gary K.]

About to order the CS165R cam for '68 427/435 build. The old cam PN3863144 has what looks like the rear groove I have read so much about (photo). From research my motor is '73 CE block 3999289 427 build up not 454 configuration. This is the cam that came installed. From earlier thread '03:

"...only the 65 and 66 BBC need the groved rear cam journal. if you use a grooved cam in a later block you have a big oil loss internally and this could could cause you valvetrain wear because not enought oil is getting to the parts."

My reason for rebuild was a couple bent pushrods, flattened lobes, couple toasted piston tops. I thought it was lack of valvetrain adjustment + maybe bad gas but could it have been the grooved cam. I want to order the CS165R cam without the groove but if I do so are there other precautions needed to ensure proper oil flow to valve train. Thank You!!
CAM00538 (1).jpg

[Duke W.]

Re: Cam Groove in '73 CE motor w/photo - did this cause bent pushrods

The differences between the '65-'66 and '67-up big block oiling system have been discussed many times, so you should do some archive searching.

The current CS165R cam does not have the groove according to recent purchase reports, and I don't expect your '73 vintage CE block needs one, though your should verify. The rear cam bearing should have one hole and there should be a groove machined in the block centered fore/aft on the rear camshaft bearing bore. You will have to remove the bearing to see this.

Beyond this, it's okay to run either a grooved or non-grooved rear journal cam in a '67-up type block, but the '65-'66 blocks MUST have a camshaft with a rear journal groove along with a "three-hole" rear bearing. In these early blocks the oil passage to the lifter galleries is the groove in the journal, and the two extra holes in the bearing. On the '67-up blocks it's the groove in the block the surrounds the rear cam bearing.

The Chevrolet Power Manuals from the seventies specified a modification to the single hole rear bearing if you were using a grooved rear journal cam in a '67-up block, but this advice was later rescinded.

There have been reports from big block owners of no oil to the rockers after a rebuild, and most were traced to having a single hole bearing in the early blocks that require the three hole bearing.

Without understanding more about the operational and maintenance history of this engine it's be impossible to offer anything other than a wild guess as to why it has lobe, pushrod, and piston damage. I'm sure it has nothing to do with the cam journal groove. The ...143 cam/pin assembly with the rear journal groove was in the P&A catalog for years as the service replacement for all '65-'71 SHP big blocks.

You should also determine what valve springs are installed - first or second design OE? Aftermarket?

Duke

[Joe R.]

Re: Cam Groove in '73 CE motor w/photo - did this cause bent pushrods

Gary,

Are you using CJ-4 oil?

Joe

[Joe L.]

Re: Cam Groove in '73 CE motor w/photo - did this cause bent pushrods

The differences between the '65-'66 and '67-up big block oiling system have been discussed many times, so you should do some archive searching.

The current CS165R cam does not have the groove according to recent purchase reports, and I don't expect your '73 vintage CE block needs one, though your should verify. The rear cam bearing should have one hole and there should be a groove machined in the block centered fore/aft on the rear camshaft bearing bore. You will have to remove the bearing to see this.

Beyond this, it's okay to run either a grooved or non-grooved rear journal cam in a '67-up type block, but the '65-'66 blocks MUST have a camshaft with a rear journal groove along with a "three-hole" rear bearing. In these early blocks the oil passage to the lifter galleries is the groove in the journal, and the two extra holes in the bearing. On the '67-up blocks it's the groove in the block the surrounds the rear cam bearing.

The Chevrolet Power Manuals from the seventies specified a modification to the single hole rear bearing if you were using a grooved rear journal cam in a '67-up block, but this advice was later rescinded.

There have been reports from big block owners of no oil to the rockers after a rebuild, and most were traced to having a single hole bearing in the early blocks that require the three hole bearing.

Without understanding more about the operational and maintenance history of this engine it's be impossible to offer anything other than a wild guess as to why it has lobe, pushrod, and piston damage. I'm sure it has nothing to do with the cam journal groove. The ...143 cam/pin assembly with the rear journal groove was in the P&A catalog for years as the service replacement for all '65-'71 SHP big blocks.

You should also determine what valve springs are installed - first or second design OE? Aftermarket?

Duke

Duke-----


The 3999289 block will have the 67+ rear cam journal configuration unless it's some sort of factory mistake. I highly doubt that.

It sounds like this engine "started life" as a SERVICE SHP 427, either a complete engine or short block assembly. Of course, what mods may have been been performed post-factory is anyone's guess at this point.

[Duke W.]

Re: Cam Groove in '73 CE motor w/photo - did this cause bent pushrods

I've always assumed that a non-grooved cam was used on '67-up Tonawanda-built blocks, but here we have what appears to be a '73 vintage service replacement short block that has a grooved cam. Could it be that the non-grooved cam was tabled and grooved cams continued to be used in production?

Given that the grooved cam was always the service replacement other than your report that a number of non-grooved cams were found years later and showed up in the parts book until the supply was exhausted.

Then there is the valve spring issue. The second production design 3970627 dual spring was verified by Joe Raine to have a rate of 454 lbs/in, yet the 3916164 HD spring is listed in the GMPP catalog with a rate of 358 lb/in. Maybe this rate is incorrect. It doesn't make sense that the production spring (other than HD) would have 27 percent greater rate than the HD spring.

Forty years after GM stopped installing big blocks in Corvettes this has yet to be sorted out.

Duke

[Gary K.]

Re: Cam Groove in '73 CE motor w/photo - did this cause bent pushrods

[QUOTE=Joe Raine (45823);697979]Gary,

Are you using CJ-4 oil?

No - it had SAE10W-30 API, probably Castrol my usual brand.

Thank You, GK

[Joe L.]

Re: Cam Groove in '73 CE motor w/photo - did this cause bent pushrods

I've always assumed that a non-grooved cam was used on '67-up Tonawanda-built blocks, but here we have what appears to be a '73 vintage service replacement short block that has a grooved cam. Could it be that the non-grooved cam was tabled and grooved cams continued to be used in production?

Given that the grooved cam was always the service replacement other than your report that a number of non-grooved cams were found years later and showed up in the parts book until the supply was exhausted.

Then there is the valve spring issue. The second production design 3970627 dual spring was verified by Joe Raine to have a rate of 454 lbs/in, yet the 3916164 HD spring is listed in the GMPP catalog with a rate of 358 lb/in. Maybe this rate is incorrect. It doesn't make sense that the production spring (other than HD) would have 27 percent greater rate than the HD spring.

Forty years after GM stopped installing big blocks in Corvettes this has yet to be sorted out.

Duke

Duke------


This might not be the cam that was originally installed in this SERVICE engine. Someone could have changed that somewhere along the way.

Also, by 1973 it could be that SERVICE cams were being installed in these SERVICE engines and, at that time, the grooved rear journal cam was the SERVICE cam for all 65-71 SHP big blocks. At that time, SHP big blocks were 2 years out of PRODUCTION use.

[Joe R.]

Re: Cam Groove in '73 CE motor w/photo - did this cause bent pushrods

Gary,

This is likely why you flattened your cam. Don't ask me how I know this. I would highly recommend using CJ-4 oil after reading this article, scroll down to page 3:

http://stlouisncrs.org/news_files/St_Louis_NCRS_Chapter_July_2011.pdf#page3

Joe

[Gary K.]

Re: Cam Groove in '73 CE motor w/photo - did this cause bent pushrods

I thank everyone for your input. For the record my '73 #CE363481 date B 12 73 block I am 100% positive came with the grooved cam pictured. The motor was never worked on again after install in early 1975. Also - the last time I had valve covers off before valve train failure I saw plenty of oil - enough to want to get the little splash guards so I believe oiling was fine and probably will be "without the groove" when I get the CS165R in there. If not I will report it...

[Duke W.]

Re: Cam Groove in '73 CE motor w/photo - did this cause bent pushrods

There's no reason for oil splash. The valve lash can be set with the engine cold and not running. The procedure is widely available on the Web - google Hinckley Williams valve adjustement, and download the paper from the lbfun website. Be sure it is the latest revision, which is September 2008. Use the specified indexing procedure, and I recommend cold clearances of .020/.022" inlet/exhaust.

You should attempt to determine the cause of the flattened lobes. I asked about the valve springs and heads, but you did not respond, so I repeat the question. The use of SM or SN oil could also be a contributing cause.

You mentioned "toasted" piston tops. Can you be more explicit? Photos would help.

Providing additional information on the damage should help you avoid similar problems in the future. It will also be beneficial to others by helping them avoid the same problems.

Duke

[Gary K.]

Re: Cam Groove in '73 CE motor w/photo - did this cause bent pushrods

Unfortunately the "ka-pang" moment occurred at 60+ mph while accelerating, then had to limp about a mile to a proper place to pull off. Its tough to figure out exactly what went wrong. I have two bent push rods, a couple flattened lobes, corresponding surface scoring on a couple lifters but a lot of that cam damage could have come during those final minutes. Valves springs - mystery, installed 1975 I can only assume stock replacement. Piston tops smell like burned oil, kind of oily black residue not dry/orange like the other vlaves/p-tops but again - how much of that is recent and how much 35-40,000 miles of driving. That is extent of damage, machine shop magged & found no block, piston, rod or other lower end damage. Oil - I don't think so, I use Castrol SAE10W-30 API type as shown in '68 manual. I hope this does help others, I've moved on with a rebuild.

DSC00431.jpg DSC00404.jpg

[Duke W.]

Re: Cam Groove in '73 CE motor w/photo - did this cause bent pushrods

Oil - I don't think so, I use Castrol SAE10W-30 API type as shown in '68 manual. I hope this does help others, I've moved on with a rebuild.

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Thanks for the additional information. A wearing cam lobe will cause valve toss at ever lower revs, and when it finally happens and the valve comes crashing back down, pushrods can bend.

Piston deposits can mean many things, but not necessarily piston damage. I don't see any obvious piston damage except, maybe on #7, but it's difficult to tell with one photo and not all pistons are at TDC. The crowns must be cleaned off, and then you can inspect for detonation damage. Light detonation over a sustained period may be indicated by tiny pin holes - the crown may look like it was attacked by an ice pick. Heavier detonation can result in a missing chunk.

The end cylinder that has black deposits on both valves may indicate excess oil flow to that cylinder. It could also mean that the cylinder was not firing because oil deposits on exhaust valves usually carburize to white to tan. Perhaps it was one of the cylnders with a worn cam lobe.

OE valve springs usually have a dab of colored paint to ID them. The prone to break first design big block valve springs are a single spring/damper design. The second design that went into production circa 1969 is a dual spring design with integral umbrella seal. You should have the installed springs tested to see if they are reasonably within OE spec, and if not replace them with something similar. Stiffer than OE valve springs for the OE-spec cam is a recipe for lobe failure.

You statement about oil including "API type" indicates that you are decades behind in oil formulation and service categories. Engine oils available today are very different than 1968. I can only advise you take the time to download and thoroughly read/understand the link in post #8, which should get you up to speed on current engine oils and what is best for vintage engines.

Whenever one is confronted with an unexpected failure, an effort should be made to determine the cause. (I did considerable failure analysis work in my engineering career including my first task as a freshly minted BSME and Pontiac production engineer - failing wheel bearings in 1968.) Otherwise the same thing can happen down the road.

Duke