From my other thread...am helping a family friend w/ a rebuild. Everything I've read says there is no cam button or retainer required, as has been the case when looking @ the engine as well (there isn't anything). Does the distributor gear in combo w/ the timing chain hold her in place? Seems strange to me, not having a positive retainer where a running clearance can be established. Am looking for confirmation that we don't need to add anything, thanks.

 

I am not familiar with your other thread. What engine are you working on?

 

85 SBC, IROC TBI. Everything I've found says that the cam is self contained. This makes me nervous. There is no cam retaining plate & no timing cover button. The cam position seems to be maintained by timing chain & distributor gear.

 

If its a flat tappet cam then there is no retaining plate. The lifters and the distributor keep the cam in the block. The way the lobes are cut, the lifters force the cam back.

It wasn't until roller cams that they started using a retaining plate/button.

 

Yah, it's a flat tappet. Thanks for the confirmation. I'm still gonna weld a button to the timing cover...just don't feel right leaving it alone. Does .015" sound about right for clearance?

 

IMO I would leave it alone. Engines didn't have retaining plates in them for 30+ years.

The cam isn't going anywhere.

 

the only engines to have retainers for the cam are ones with roller cams

 

Yah, OK, I'll leave it alone. It just freaked me out. Thanks again.

 

lol kids.

 

I'm no kid, just don't have the experience w/ "OLD" SBC technology.

 

haha nice dig btw.. *old*. Btw it's not just Chevy, pretty much every non-roller flat tappet engine doesn't make use of a cam button, nor do many belt drive overhead cams.

 

in case you don't know,
since it's a flat tappet when you first start it up you want to immediately get the rpms between 2000-2500 for at least 10-15 minutes to break in the cam and lifters. The high speed ensures good oil flow and that the lifters spin in their bores. Do not start it up and idle it tinkering with idle mixture or timing, you need to get those set up prior to starting the motor.
Using a moly paste on the cam lobes prior to installing is a good idea,
and using something like GM EOS (engine oil supplement) with extra ZDDP additive is also a good idea on the initial oil fill and break in. Definitely use a zddp additive if you have higher than stock valve spring pressures, if you're using upgraded valve springs.

 

Thanks for that. I knew about the zinc, but not about initial start-up. Was gonna let it warm up for 2-3 heat cycles & then spin faster. Now, will spin as you noted during the first few heat cycles. Thanks again.

 

Good post. Comp also suggests if you are running a dual valve spring to take the inner spring out during break in. Yes I know it's a lot of work, but so is grinding off a new cam. Trust me I know.

 

at the risk of insighting the break-in method debate...

don't worry about "heat-cycling".
the hardest part of doing an engine rebuild is having ignition timing and fueling correct for initial startup and then being able to run the motor properly for at least the first half hour to get proper seating of the piston rings and in your case also the flat tappet camshaft.

What you want to do is prime the engine oil pump first to make sure oil is pressurizing the main bearings and oil pushes up into the lifters. Do this prior to installing the intake, so you can see the lifters. Then prior to installing the valve covers pour a quart of oil over the valve train on each head. Last thing you want to happen on that first startup is to not get oil pressure on all new parts. You want immediate oil pressure. You also want it to start and have adequate timing to run, anywhere from 8-14 dBTDC will do. If your base timing is supposed to be 10 and you have 8 or 12 don't worry about it, it will do. And if you're carbed you don't want an overly rich mixture, if anything go on the leaner side. But you do need the mixture correct enough to put a load on the engine and not have it bog out or backfire, or detonate obviously.
On first fire up bring the rpms immediately up to 2000 and vary the rpms between 1800-2500 for the first 5 minutes, this ensures adequate oil flow to the cam lobes and lifters, and this is your warm up and time to check no fluids leaking, timing is ok, mixture is good enough. Then as little and as infrequent as possible drop down below 1500 rpm to get into gear. Then get the rpms back up over 1500 and vary rpms between that and up to around 3500 for the next half hour with the engine under medium load, hopefully not driving people off the road. This is your piston ring break in, it's load on the engine which causes piston rings to wear in evenly and seal. So you don't want to drive like grandma on flat roads, find some hills to go up and put some load on the engine, varying rpms between 1500 up to around ~3500. You don't want to wind it out to redline at 5500 rpms, and you don't necessarily want to run at a constant 3500-4000 rpm nor overload or lug the engine. This is where opinions vary, some say beat the crap out of it but most will agree to put some decent load on the motor to seat the rings. piston ring break in happens from initial start up, so the sooner you get the engine under a moderate load the better.