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MG MGA - Replace One or All Tappets?

I know I have at least one bad tappet. Should I replace all of them or just locate the bad one(s)? I ask because I have seen numerous comments about how tappets should always go back in the same hole they came from but I don't know why so I wonder if it is best to just replace all of them.
Steve

Steve

I am not an engineer, but gut feeling says replace them all while you have the engine stripped down that far.

Make sure you coat the mating face with an installation grease when assembling. I was told that you can ruin new tappets if installed dry.

Steve
Steve Gyles

Most flat tappets and cams are designed to rotate the tappet as they work. Because of this the tappet and cam lobe develop a matching wear pattern and should be kept matched during any rebuild. Installing one new tappet on the cam shouldn't cause any problems if it's properly lubricated and a good break in procedure used, check your tappet manufacturer or cam manufacturers recomendations. I have heard the horror stories about the quality of new tappets, but would still recommend replacing all the tappets as a set if you can afford to do so. If the tappet has failed then the cam should be checked very carfully also. A worn lobe can ruin a new tappet quickly. Sounds like the safest thing to do would be replace both the cam and tappets at the same time, and you can get a bit of power increase in the process as a bonus if you're running a stock cam.
Bill Young

Thanks Steve and Bill -
The engine was recently rebuilt and I suspect the old tappets were used, not sure about the cam. I was planning on just doing tappets from the side, not breaking down the whole engine.
Cost is not a big concern (within limits!!) and I notice Moss has four different tappet selections; regular at $64/set, lightened set for $70, super duty for $125 and tested tappets for $160. Any recommendations from that list?
Solvang Steve
Steve

Hi You could fit the lighter MGB type, but you will have to change the pushrods aswell, Moss sell a lightened set. As mentioned, its no use fitting new tappets on a worn cam. You should check the rocker gear aswell, this is often overlooked and can cause tappet noise. I always use Kent or Piper MGB type followers.


Regards

Terry
Terry Drinkwater

Hi Steve. If old tappets were used with a new camshaft, the new camshaft could well be damaged (premature wear). The camshaft needs to be carefully inspected and measured for any abnormal wear. If the camshaft is significantly worn, or has damaged lobes, it should be replaced. If the camshaft is not worn, then I would definitely replace all the lifters. When you install new lifters, you MUST use moly based lubricant, or the cam and lifters will fail prematurely. Apparently only moly based lubes have adequate film strength to protect moving parts during break in. You can use Moly based chassis grease as lubricant if you wish. Additionally, on engine start up, the engine should NOT be allowed to idle for the first 15 minutes. The engine should be run constantly at around 1500 to 2000 RPM to load the lifters so they break in properly. Additionally, immediately after starting the engine, you should check to see that all the pushrods are spinning. Do this by feeling them with your fingers. If any pushrods are not spinning, you should manually turn them with your fingers until they start to spin and stay spinning. Hope this helps, Glenn
Glenn

>When you install new lifters, you MUST use moly based lubricant, or
>the cam and lifters will fail prematurely. Apparently only moly based
>lubes have adequate film strength to protect moving parts during
>break in.

That's just not true. Use of an assembly lube is critical, and a special cam lube containing molybdenum disulfide is probably beneficial, but your cam and lifters are not going to be ruined if you use a regular assembly lube. The main characteristic for a good assembly lube is that it has to be tenacious enough to stay in place until the engine is actually run, including being turned over by hand (which tends to wipe away lubricants from wearing surfaces) prior to actual use. It's only purpose is to provide lubrication until the engine's oil system can take over and get the regular oil to all of the wearing surfaces. A secondary characteristic is that it has to be light enough that it will be washed away by engine oil and not create sludge or clog the system.

I'm in the process of (finally) re-assembling my 1500 engine and am using the same Lubriplate assembly grease with which I was taught to assemble aircraft engines. The last time my dad rebuilt the engine in 1966, I kind of doubt that he had access to a moly cam lube, but it nevertheless ran until I pulled it from the car in 1991, and the cam didn't exhibit any damage beyond the normal amount of wear you would expect to accumulate in 25 years of use.

Probably the most important thing is that the cam and lifters should be replaced as a set, as was mentioned earlier. And if you are going to re-use the old parts, the lifters need to be numbered so they can be re-installed in the same position, since each is already worn into its position. And of course parts that are already worn in together still need a coating of assembly lube.
Del Rawlins

All godd stuff, but Steve, how do you know you have one or more bad tappets?

Like Terry says, are you sure it's not the rockers/shaft that are worn. That's a more common cause for tappet noise, and easy to check. (Just waggle the rockers when not under load).

Additionally, sometimes the rocker face can exhibit recessed wear and the also adjusters can be "sticky" if overtightened during previous adjustment, both factors make accurate gap setting difficult.

Like the guys say, if you really have bad tappets better check the camshaft.

Best of luck,

Jack
JN McGurk

I suspect a lifter because the sound seems like just one "blap" and goes away (or at least greatly drops) after the engine warms up. I am going to double check the rockers and adjusters before digging in, though. My first MGA had mismatched pistons turned every which way, you should have heard it!
Thanks for all the great advice.
Steve

Hi Del. At least one manufacturer of camshafts (Crane) states that Moly based lube MUST be used in order to prevent premature camshaft and lifter damage. I have myself used lubriplate on an MGB engine overhaul many years ago. This engine ran well, but did exhibit pronounced wear on the lifter bottoms at relatively early mileage. Perhaps those lifters were been made of substandard materials or perhaps they were poorly hardened. However, for the small amount that Moly based lube costs, it seems silly (from my perspective) not to use it as a safeguard. Just my 2 cents worth, Glenn


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Reasons and Causes for Cam Failure


Cam failure is rarely caused by the cam itself. The only things we can control during manufacture pertaining to cam lobe wear are lobe taper, lobe hardness and surface finish. Of all the damaged cams we have checked over the years, more than 99.99 percent have been manufactured correctly. Some people have the misconception that it is common for a cast iron flat tappet cam to occasionally have a soft lobe. We have yet to see a cast iron flat tappet cam that had a soft lobe.

When the cast core is made at the casting foundry, all the lobes are flame hardened. That process hardens all the lobes to a depth below the barrel of the core. That depth of hardness allows the finish cam grinder to finish grind the cam lobes with a Rockwell hardness above 50Rc. The generally accepted hardness on a finished cast cam should be between 48Rc to 58Rc.

All of the finished cams that we have checked are always above 50Rc hardness on the lobes. Many outside factors, or a combination of factors, can cause cam failures. We will list some of the factors we have determined that may cause camshaft failure.

1. Lobe wear
A) Incorrect break-in lubricant.
Use only the Moly Paste, Part Number 99002-1 that is included with the cam. This Moly Paste must be applied to every cam lobe surface, and to the bottom of every lifter face of all flat tappet cams. Roller tappet cams only require engine oil to be applied to the lifters and cam. Also, apply the Moly Paste to the distributor gears on the cam and distributor for all camshafts. For extra protection, an anti-wear additive should be added, such as Crane Super Lube, Part Number 99003-1.

NOTE: Do not use synthetic oil during the break-in period. It is not recommended to use any type of oil restrictors to the lifter galley, or use windage trays, baffles,or plug any oil return holes in the valley. Oil has a two-fold purpose, not only to lubricate, but to draw the heat away from whatever it comes in contact with. The cam needs oil splash from the crankcase, and oil run-back from the top of the engine to help draw the heat away. Without this oil flow, all the heat generated at the cam is transferred to the lifter, which can contribute to it's early demise.

B) Correct break-in procedure.
After the correct break-in lubricant is applied to the cam and lifters, fill the crankcase with fresh non-synthetic oil. Prime the oil system with a priming tool and an electric drill so that all oil passages and the oil filter are full of oil. Pre-set the ignition timing and prime the fuel system. Fill the cooling system. Start the engine. The engine should start quickly and run between 1500 and 3000 rpm.

If the engine will not start, don't continue to crank for long periods, as that is very detrimental to the life of the cam. Check for the cause and correct. The engine should quickly start and be run between 1500 to 3000 rpm. Vary the rpm up and down in this rpm range during the first 15 to 20 minutes, (do not run the engine at a steady rpm). During this break-in time, verify that the pushrods are rotating, as this will show that the lifters are also rotating. If the lifters don't rotate, the cam lobe and lifter will fail. Sometimes you may need to help spin the pushrod to start the rotation process during this break-in procedure.

(a) Note: Lifter rotation is created by a taper ground on the cam lobe and the convex shape of the face of the flat tappet lifter. Also in some cases, the lobe is slightly offset from the center of the lifter bore in the block. If the linear spacing of the lifter bores in the block is not to the correct factory specifications, or the angle of the lifter bore is not 90 degrees to the centerline of the cam, the lifter may not rotate.

Even if the engine you?re rebuilding had 100,000 miles on it and the cam you removed had no badly worn lobes, this still doesn't mean that your block is made correctly. It just means that the break in procedure caused everything to work correctly. Be careful to watch the pushrods during break in to verify lifter rotation. Don't assume everything will work correctly the second time.

(b) Note: Always use new lifters on a new flat tappet cam. If you are removing a good used flat tappet cam and lifters and are planning to use them again in the same (or another) engine, you must keep the lifters in order as to what lobe of the cam they were on. The lifter breaks-in to the specific lobe it is mated with and it can't be changed. If the used lifters get mixed up, you should discard them and install a new set of lifters and break the cam in again as you would on a new cam and lifters. You can use new lifters on a good used cam, but never try to use used lifters on a new cam.

(c) Note: Roller tappet cams don?t require any break-in. You can use roller lifters over again on a new cam if they are in good condition. There will be, of course, no lifter or pushrod rotation with the use of a roller tappet cam.

C) Spring pressure
Normal recommended spring seat pressure for most mild street-type flat tappet cams is between 85 to 105 lbs. More radical street and race applications may use valve spring seat pressure between 105 to 130 lbs. For street hydraulic roller cams, seat pressure should range from 105 to 140 lb. Spring seat pressure for mechanical street roller cams should not exceed 150 lb. Race roller cams with high lift and spring pressure are not recommended for street use, because of a lack of oil splash onto the cam at low speed running to help cool the cam and lubricate the lifters. This high spring pressure causes the heat created at the cam to be transferred to the roller wheel, resulting in its early failure. Any springs that may be used must be assembled to the manufacturer?s recommended height. Never install springs without verifying the correct assembled height and pressures.

NOTE: Increased spring pressure from a spring change and/or increased valve lift can hinder lifter rotation during cam break-in. We have found that decreasing spring pressure during the break-in period will be a great help. This can be accomplished by using a shorter ratio rocker arm to lower the valve lift; and/ or removing the inner spring, during the cam break-in time, if dual springs are being used.

D) Mechanical interference.
There are many factors that can cause mechanical interference.

(1) Spring coil bind: This is when all of the coils of the spring (outside, inside or flat damper) contact each other before the full lift of the valve. We recommend that the spring you are using be capable of traveling at least .060" more than the valve lift of the cam from its assembled height.

(2) Retainer to seal/ valve guide boss interference. You need at least .060" clearance between the bottom of the retainer and the seal or the top of the valve guide when the valve is at full lift.

(3) Valve to piston interference: this occurs when a change in cam specs. (i.e.; lift, duration or centerline) is enough to cause this mechanical interference. Also: increased valve size, surfacing the block and/or cylinder head may cause this problem. If you have any doubt, piston to valve clearance should be checked. Minimum recommended clearance: .080" intake and .100" exhaust.

(4) Rocker arm slot to stud interference: As you increase valve lift, the rocker arm swings farther on its axis. Therefore the slot in the bottom of the rocker arm may run out of travel, and the end of the slot will contact the stud and stop the movement of the rocker arm. The slot in the rocker arm must be able to travel at least .060" more than the full lift of the valve. Some engine families, like small block Chevrolet, have stamped steel rocker arms available in long and extra long slot versions for this purpose.

2) Distributor gear wear.
The main cause for distributor gear wear is the use of high volume or high-pressure oil pumps. We don?t recommend the use of these types of oil pumps. If you do run these types of oil pumps, you can expect short life of the cam and distributor gears, especially for low speed running, in street type applications. If you must run these types of oil pumps, you can increase the life of the gears by adding more oil flow over the gear area to help cool off the point of contact.

NOTE: distributors that have end play adjustment (up and down movement of distributor shaft and gear), Maintain a maximum of .010" end play, to help prevent premature wear.

3) Camshaft end play.
Some engines have a thrust plate to control the forward and backward movement of the cam. The recommended end play on these types of engines is between .003" to .008". Many factors may cause this end play to be changed. When installing a new cam, timing gears, or thrust plates, be sure to verify end play after the cam bolts are torqued to factory specs. If the end play is excessive, it will cause the cam to move back in the block, causing the side of the lobe to contact an adjacent lifter.

4) Broken dowel pins or keys.
The dowel pin or Woodruff key does not drive the cam; the torque of the timing gear bolt, or bolts, against the front of the cam drives the cam. Some reasons for the dowel pin or key failing are: Bolts not being torqued to correct specs; Incorrect bolts of a lower grade being used; Stretching and losing torque; Not using the correct hardened washer that may distort and cause torque of the bolt to change; LocTite not being used; Or some interference with the cam and lifters or connecting rods causing the cam to stop rotation.

5) Broken cam
A broken cam is usually caused by the cam being hit by a connecting rod, or other rotating parts of the engine coming loose and hitting the cam. When this happens, the cam will usually break in more than two-pieces. Sometimes the cam will break in two pieces after a short time of use because of a crack or fracture in the cam due to rough handling during shipping, or some time before installation. If a cam becomes cracked or fractured due to rough handling, it will generally not be straight.

Most people will not have any means of checking cam straightness. As a general rule, if you can install the cam in the engine and install the timing gear, the cam should turn freely with just your finger pressure. There should not be any drag or resistance in turning the cam. This free turning of the cam is assuming that if new cam bearings were installed, they were the correct parts and they were installed correctly.

NOTE: When removing a used cam that may be worn, you may have difficulty turning or removing it. This may not mean that the cam is cracked or fractured. The heat generated at the cam during the failure of the cam lobe, and/or lifter, will distort the cam and cause it not to be straight any more




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Glenn

I've got a set of stock type lifters that I bought (most likely from SF) when I originally tore the engine down in '92, that I'm not going to be using because I have no confidence in them. The machining and finish is fairly rough in places (like where the pushrod end goes) and I ended up buying a set of pushrods and lifters from Moss later which are going into the engine (along with a new stock camshaft). You really have to wonder about the origin of some of the parts we get these days. I thought about the aftermarket parts but I'm trying to keep the engine (and car) as close to how my dad had it as possible, and besides which, problems with the "uprated" components are not unheard of either. Witness the pushrod failures documented on Barney's site. The only internal mods I have made are to fit the later oil pump (my engine missed it by about 20 units in original production), and the head/valve mods for unleaded fuel. Plus switching back to a "15" head.
Del Rawlins

Re break-in lubricant: I have been using Graphogen collodial graphite assembly lube on the camshaft and tappets. Can any of you tell me the difference between moly and graphite for this purpose?

Tore
Tore

This thread was discussed between 01/12/2006 and 06/12/2006

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