roller cam in my 75 roadster

[Ross F.]

I'm interviewing machine shops to work on my 75 L-48 motor. It has 50,000 miles on it and the car came with no service history. I looked over the motor and the rocker galleries are kind of gummy, I need to check compression. But I was thinking I'd pull the heads and get them rebuilt, but leave the bottom end alone. One shop I talked to has me thinking about a total rebuild. He claims that I should install a roller cam and lifters. The reason is today's gas formulation. Is this really an issue? I've heard of unleaded gas being an issue on valve seats in 70's cars, but not zinc on cams.

[Joe L.]

Re: roller cam in my 75 roadster

I'm interviewing machine shops to work on my 75 L-48 motor. It has 50,000 miles on it and the car came with no service history. I looked over the motor and the rocker galleries are kind of gummy, I need to check compression. But I was thinking I'd pull the heads and get them rebuilt, but leave the bottom end alone. One shop I talked to has me thinking about a total rebuild. He claims that I should install a roller cam and lifters. The reason is today's gas formulation. Is this really an issue? I've heard of unleaded gas being an issue on valve seats in 70's cars, but not zinc on cams.

Ross-----


Gasoline formulation has absolutely nothing to do with the camshaft. Oil formulation does and perhaps that's what he meant. However, you can obtain oils that will work well with flat tappet camshafts. These include diesel engine-rated oils and special performance oils fortified with extra zinc and phosphorous. You can also fortify regular oils using something like GM's Engine Oil Supplement (EOS).

Notwithstanding the above, I like hydraulic roller cams. They're expensive but I think they're the way to go. Personally, I'd be very reluctant to build another engine with a flat tappet cam. I just feel that hydraulic roller cams have made them totally obsolete. If you look at the major automotive manufacturers, they haven't made an in-block cam engine in more than 20 years with anything but an hydraulic roller cam. Of course, fuel economy is part of the reason but it's NOT all of the reason.

[Ross F.]

Re: roller cam in my 75 roadster

Joe, its oil, my mistype.
I've been reading old posts on this subject. And I have more questions than I started with!
Like, can you put a roller cam in a 75 block? I read about camshaft stop plates, spinning roller lifters. What are the issues in a cam swap? Who's cam do I buy? What grind? Overlap? New springs, rockers? Argh!

[Joe L.]

Re: roller cam in my 75 roadster

Joe, its oil, my mistype.
I've been reading old posts on this subject. And I have more questions than I started with!
Like, can you put a roller cam in a 75 block? I read about camshaft stop plates, spinning roller lifters. What are the issues in a cam swap? Who's cam do I buy? What grind? Overlap? New springs, rockers? Argh!

Ross-----


Yes, you can install a roller cam in a 1975 small block. However, what you need is a RETROFIT hydraulic roller camshaft. These are different in several ways from those installed OEM on 1987+ Gen I and II small blocks. RETROFIT hydraulic roller camshafts use lifters coupled in pairs with an anti-rotation bar between them. No other anti-rotation devices are required.

OEM roller camshafts use a thrust plate for camshaft thrust control. This requires the block to be designed for and machined for such plate installation. Retrofit hydraulic rollers use a cam button for thrust control.

A RETROFIT hydraulic roller camshaft installation requires the camshaft, a set of coupled hydraulic roller lifters, a cam button, and specific length pushrods. Often times, these can be purchased as a kit. You can use stock rocker arms and stock valve springs (as long as you go with a mild grind, as you should).

I would stay with a cam grind that has no more than 220 degrees intake duration at 0.050" valve lift.

[Patrick H.]

Re: roller cam in my 75 roadster

Check the compression.

If the cylinders are relatively well balanced I would install new valve guide seals on the motor and be done. 50,000 miles is not a big deal on these engines, especially as Corvettes tend to be weekend cruisers more than anything else.
But, it's your car and your money.

[Duke W.]

Re: roller cam in my 75 roadster

What Patrick said... Minor to moderate sludge buildup is not a big deal. If the engine has good compression/leakdown and performs almost like new, why spend several thousand rebuilding the engine? (But if you do, find another shop. This guy is clueless.)

I don't think roller cams are worth the cost, which is a lot more than a replacement flat tappet cam. Massaging the heads is more cost efficient, but the biggest performance impediment is the single catalyst exhaust, which has huge pumping loss at high revs, so there's no point trying to improve internal engine performance unless you are willing to do something with the exhaust system, which means the car will no longer meet emission requirements. Eighty percent of it will be eaten up by increased exhaust pumping power.

Use of CJ-4 oil provides more than adequate protection for OE valvetrains.

Duke

[Patrick H.]

Re: roller cam in my 75 roadster

the biggest performance impediment is the single catalyst exhaust, which has huge pumping loss at high revs, so there's no point trying to improve internal engine performance unless you are willing to do something with the exhaust system, which means the car will no longer meet emission requirements. Eighty percent of it will be eaten up by increased exhaust pumping power.

Duke

Amen.
Without trying to offend, you're starting with a 1975, the lowest performance Corvette made. Just enjoy the car, as I think you'd be throwing away $.
Tuning the carb and the ignition will give you far more "bang for your buck" than rebuilding and modifying it.

Patrick

[Timothy B.]

Re: roller cam in my 75 roadster

Amen.
Without trying to offend, you're starting with a 1975, the lowest performance Corvette made. Just enjoy the car, as I think you'd be throwing away $.
Tuning the carb and the ignition will give you far more "bang for your buck" than rebuilding and modifying it.

Patrick

What Patrick and Duke said... You are getting talked into a job that will cost $$$ and you are not prepared to engineer this change. If it's only got 50,000+- miles chances are nothing is wrong with the engine.

If it's not apart, inspect and clean the lifter gallery yourself and inspect the lifters looking at the bottom for ware. This will tell you the condition of the camshaft, make sure you keep the lifters in the same hole they have lived in for the last 39 years if you decide to use them. If you change the camshaft and lifters because of ware get a Federal Mogul replacement of the same size so everything works together.

[Ross F.]

Re: roller cam in my 75 roadster

Ok, lots of diverse opinions. Performance enhancement isn't what I am going for. I have the car in pieces, and while its out, why not go through the motor? Yes, I have caught the disease. I will probably have the only $50,000.00 75 roadster on the planet. But " ye, who is without sin, let him cast the first stone". That being said. I am probably just going to clean, inspect, and install new gaskets. what kind if compression should I be looking for? If I pull the lifters to inspect them, do I have to dynanically adjust the rockers. Or is 1/2 turn past snug ok?. Yes the exhaust is an issue for performance. Thinking about that. The cat is long gone. I cant find an original. I have a new hi flow unit. Given that, judging wise, how much worse is it to go to duals?

[Michael W.]

Re: roller cam in my 75 roadster

But I was thinking I'd pull the heads and get them rebuilt,

Why? If there's no evidence of anything being wrong with the engine, leave it alone. 50K miles on a '75 L48 means that it's barely broken in.

[Duke W.]

Re: roller cam in my 75 roadster

A better check for cam wear is to measure lobe lift with a dial indicator, and this can be done without removing the manifold.

Lobe lift and compression data is in the CSM. Unless oil consumption is more than a quart in 500-1000 miles I wouldn't bother rebuilding the heads, but it would be a good idea to replace the valve stem seals, which is usually the first cause of oil consumption. Of course, if you change the seals you'll have to adjust the valves. With each cylinder at TDC of the compression stroke, tighten the rocker nut on both valves until you can't feel clearance. (Wiggle the pushrod up and down.) Then add 1/2 - 1 turn.

A modern replacement cat has lower backpressure than the OE cat, but the exhaust system is still restrictive.

The sludge buildup is probably due to lack of oil changes or short trips. Just check out the PCV system/valve and make sure it's fully functional.

Base 350s of that era don't have a lot of top end power, but they are torquey and responsive in normal road driving. By far the best bang for the buck to improve performance and fuel economy is to optimize the spark advance map.

Duke

[Patrick H.]

Re: roller cam in my 75 roadster

I am probably just going to clean, inspect, and install new gaskets.

Why, is it leaking? If the intake and/or head gaskets aren't leaking I would highly recommend leaving them alone.

[Dennis O.]

Re: roller cam in my 75 roadster

The eight most expensive words : "While I'm at it, I might as well..."

[Steven B.]

Re: roller cam in my 75 roadster

The old saying fits --- "If it ain't broke don't fix it."

[Joe L.]

Re: roller cam in my 75 roadster

Ok, lots of diverse opinions. Performance enhancement isn't what I am going for. I have the car in pieces, and while its out, why not go through the motor? Yes, I have caught the disease. I will probably have the only $50,000.00 75 roadster on the planet. But " ye, who is without sin, let him cast the first stone". That being said. I am probably just going to clean, inspect, and install new gaskets. what kind if compression should I be looking for? If I pull the lifters to inspect them, do I have to dynanically adjust the rockers. Or is 1/2 turn past snug ok?. Yes the exhaust is an issue for performance. Thinking about that. The cat is long gone. I cant find an original. I have a new hi flow unit. Given that, judging wise, how much worse is it to go to duals?

Ross------


One thing to ponder: do you KNOW that this car has 50,000 miles on it OR is that just what's shown on the odometer? With respect to these older cars with 5 digit odometers, high mileage cars become "low mileage" cars when the odometer turns over. Personally, I believe that many of these older "low mileage" cars fall into this category.

The sludge situation you describe could be caused by several things. It could, of course, be caused by a lot of short trips AND lack of at least annual oil change. That would be consistent with a real low mileage car.

However, it could also have been caused by a high mileage car that never had regular oil and filter changes. Some folks just add oil as needed and figure that keeps the oil "fresh".

Something else that could highly exacerbate sludge formation with either of the above situations is someone foolishly using non-detergent motor oil, usually because some idiot told them it was better. Such motor oil is hard to find nowadays but once-upon-a-time it was easily available.

I have never found a practical and effective way of "de-sludging" an engine other than tearing it down. At that time, one can replace whatever parts need replacing and re-use the rest.