Lifter?
05-12-2005, 11:21 PM
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Lifter?
I have a '94 lt1 .This is my first OHV V-block engine. Could somebody please explain what lifters are and the differnt kinds. I know everythign about OHC and DOHC designs but i and havent the hardest time tryign to understand the parts of an OHV.
05-12-2005, 11:48 PM
#2
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I have to congratulate you in knowing everything about OHC engines. I just wish I could say the same thing about pushrod engines.
Lifters, also commonly referred to as tappets, are mechanical or hydraulic/mechanical devices (depending on which type you're referring to) that are located in the block between the lobe of the camshaft and the pushrod. There's one lifter for each intake lobe and one for each exhaust lobe.
The block on a V8, has 16 holes cast into it; each accomodates one lifter. So you drop the lifter in the hole, then drop a pushrod on top of it, with one end in the lifter and the other end in the rocker arm.
Both lifters/tappets and pushrods aren't found on OHV engines.
There are basically four types of lifters. There a few other "specialty" types, but the most commonly used are:
Mechanical Flat Tappet
Hydraulic Flat Tappet
Mechanical Roller
Hydraulic Roller
The type of lifter used depends on the camshaft selected, since there are also basically four different types of camshafts.
As an example, a hydraulic, flat tappet camshaft should use hydraulic flat tappet lifters. So the collar has to match the cuff, as we say. If you noticed, I used the word "should" because there are those who will install mechanical, flat tappet lifters on a hydraulic cam, but that's not the normal way of doing business.
A hydraulic lifter, either flat tappet or roller, has several moving parts inside it. A spring, plunger, etc. Oil is metered through the lifter as the engine runs and since that is no gap - or lash involved, a hydraulic lifter has quieter operation than it's mechanical counter-part.
The down\side is that a hydraulic lifter is somewhat RPM limited. Much over 6500 RPM and the lifter pumps up with oil and causes the engine power to just about die. Power drops off the table. Engine damage can result too if the valve is held open too long and the piston kisses it.
A mechanical lifter, either flat tapper or roller, is not RPM limited and will continue to rev until some part of the engine breaks or the engine blows.
Flat tappet lifters are just as the name implies, flat on the bottom; the part that rides on the camshaft lobe. Well, actually, the bottom isn't actually flat, but you'd have to look really closely to be able to tell that it's not.
Roller lifters, again as the name implies, has a roller wheel on the end that rides on the camshaft lobe. Running a roller lifter allows the cam to be designed with more radical - aggressive/steep - ramps, resulting in greater area under the curve and, for a given duration, makes more power.
The downside for a roller lifter is that it's heavier than it's flat tappet counter-part so it calls for more spring to control that extra weight. They're also much more expensive. Now when you factor in the weight of the oil inside the hydraulic roller lifter, the cost, well, you can see where I'm headed.
All these lifters have a holes in the side of the lifter body to allow oil to travel through.
Roller lifters and taller than their flat tappet cousins, so a different length pushrod is called for. Rollers and flat tappets don't take the same length pushrod.
This is just kind of a basic explanation.
Hope it helps.
Jake
Lifters, also commonly referred to as tappets, are mechanical or hydraulic/mechanical devices (depending on which type you're referring to) that are located in the block between the lobe of the camshaft and the pushrod. There's one lifter for each intake lobe and one for each exhaust lobe.
The block on a V8, has 16 holes cast into it; each accomodates one lifter. So you drop the lifter in the hole, then drop a pushrod on top of it, with one end in the lifter and the other end in the rocker arm.
Both lifters/tappets and pushrods aren't found on OHV engines.
There are basically four types of lifters. There a few other "specialty" types, but the most commonly used are:
Mechanical Flat Tappet
Hydraulic Flat Tappet
Mechanical Roller
Hydraulic Roller
The type of lifter used depends on the camshaft selected, since there are also basically four different types of camshafts.
As an example, a hydraulic, flat tappet camshaft should use hydraulic flat tappet lifters. So the collar has to match the cuff, as we say. If you noticed, I used the word "should" because there are those who will install mechanical, flat tappet lifters on a hydraulic cam, but that's not the normal way of doing business.
A hydraulic lifter, either flat tappet or roller, has several moving parts inside it. A spring, plunger, etc. Oil is metered through the lifter as the engine runs and since that is no gap - or lash involved, a hydraulic lifter has quieter operation than it's mechanical counter-part.
The down\side is that a hydraulic lifter is somewhat RPM limited. Much over 6500 RPM and the lifter pumps up with oil and causes the engine power to just about die. Power drops off the table. Engine damage can result too if the valve is held open too long and the piston kisses it.
A mechanical lifter, either flat tapper or roller, is not RPM limited and will continue to rev until some part of the engine breaks or the engine blows.
Flat tappet lifters are just as the name implies, flat on the bottom; the part that rides on the camshaft lobe. Well, actually, the bottom isn't actually flat, but you'd have to look really closely to be able to tell that it's not.
Roller lifters, again as the name implies, has a roller wheel on the end that rides on the camshaft lobe. Running a roller lifter allows the cam to be designed with more radical - aggressive/steep - ramps, resulting in greater area under the curve and, for a given duration, makes more power.
The downside for a roller lifter is that it's heavier than it's flat tappet counter-part so it calls for more spring to control that extra weight. They're also much more expensive. Now when you factor in the weight of the oil inside the hydraulic roller lifter, the cost, well, you can see where I'm headed.
All these lifters have a holes in the side of the lifter body to allow oil to travel through.
Roller lifters and taller than their flat tappet cousins, so a different length pushrod is called for. Rollers and flat tappets don't take the same length pushrod.
This is just kind of a basic explanation.
Hope it helps.
Jake
Last edited by JAKE; 05-12-2005 at 11:54 PM.
05-13-2005, 12:04 AM
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Your SBC has a single cam driven off a chain to the crank shaft, turning at 1/2 the crank shaft speed.
On either side of the block there are holes that contain valve lifters which ride on the cam lobes. Your engine uses roller lifters and a roller cam, as opposed to a flat tappet lifter and cam.
Sitting in a depression in the top of each lifter is a push rod that passes up through slots in the cylinder head.
Atop the cylinder head are rocker arms attached by a rocker arm studs to the head. The push rod from the lifter sits in a pocket under one end of the rocker arm and the other end of the rocker arm rests on the valve tip.
Each valve has an oil seal, a valve spring, a valve retainer atop the spring and retainers (or "keepers") that sit in a groove withing the retainer pinching into a grove in the valve stem and holding the spring and retainer in place.
When the cam rotates the lifter and push rod move up/down, following the cam lobe. This motion causes the rocker arm to "rock" which opens/closes the valve.
Hope this gives you an over view of the SBC valve control. For more detailed info do some reading on Comp Cams. site.
If you intend on doing any serious mods you really need to pick up a copy of the GM Shop Manual by HELM for your year Vette.
On either side of the block there are holes that contain valve lifters which ride on the cam lobes. Your engine uses roller lifters and a roller cam, as opposed to a flat tappet lifter and cam.
Sitting in a depression in the top of each lifter is a push rod that passes up through slots in the cylinder head.
Atop the cylinder head are rocker arms attached by a rocker arm studs to the head. The push rod from the lifter sits in a pocket under one end of the rocker arm and the other end of the rocker arm rests on the valve tip.
Each valve has an oil seal, a valve spring, a valve retainer atop the spring and retainers (or "keepers") that sit in a groove withing the retainer pinching into a grove in the valve stem and holding the spring and retainer in place.
When the cam rotates the lifter and push rod move up/down, following the cam lobe. This motion causes the rocker arm to "rock" which opens/closes the valve.
Hope this gives you an over view of the SBC valve control. For more detailed info do some reading on Comp Cams. site.
If you intend on doing any serious mods you really need to pick up a copy of the GM Shop Manual by HELM for your year Vette.
05-13-2005, 11:52 AM
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Originally Posted by compulsivehp
I have a '94 lt1 .This is my first OHV V-block engine. Could somebody please explain what lifters are and the differnt kinds. I know everythign about OHC and DOHC designs but i and havent the hardest time tryign to understand the parts of an OHV.
RACE ON!!!
05-13-2005, 01:41 PM
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Thanks guys. I already have the factory manual and learned that leason rebuilding Toyota. So if i am readign correctly i am looking for mechanical lifters if i want higher RPM's. I thinking of a turbocharged 383 stroker with 6in rods. This would keep my rod ratio is about 1.6 and I would like to reliably reach a 7k redline.
05-13-2005, 02:03 PM
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Originally Posted by compulsivehp
So if i am readign correctly i am looking for mechanical lifters if i want higher RPM's.
RACE ON!!!
05-13-2005, 03:09 PM
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Since you have a '94 a roller cam is the way to go.
To reliable pull to 7k RPM you need to deal with the valve train as well as the bottom end.
Do some reading on what the General did to get the engine in the C6 Z06 to rev up there. If you follow their lead you should have a very reliable high reving beast.
To reliable pull to 7k RPM you need to deal with the valve train as well as the bottom end.
Do some reading on what the General did to get the engine in the C6 Z06 to rev up there. If you follow their lead you should have a very reliable high reving beast.