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MG TD TF 1500 - XPAG Cam and Lifter - Buyer Beware
ahhh ... Saturday night and a few quiet moments to catch up on my MG reading; and I have just finished an excellent article in December's issue of the TSO by Jim Finne entitled "XPAG Cam and Lifter - Buyer Beware.
It exposes the weakness in the critical interference between the holes in the cam lifter (tappet) that allow for oil circulation to the cam lobes and the clearance in the cam ‘chamber' above the cam, especially in conjunction with the fitting of a modern camshaft. I am frankly, quite surprised that this issue has never come to light before
Its scary stuff for those like myself who have installed a new cam. So as soon as I get warmer weather, I will remove the tappet chest cover and have a look, and if in doubt, I will remove the valve gear and carefully open those suspect holes.
... and I am wondering if there has ever been an after-market product to address this?
|Gordon A. Clark|
I saw the article mentioned and as I am in the process of changing the cam and lifters, but had not yet started the enginen, I disassembled the engine again to check. I made a simple go-nogo tool to check the dimension from the top of the galley to the heel of the cam (I did not want remove the oil pan). My measurements indicate that my cam from Abingdon Spares meets the dimensions for the original cam as stated in the article and that the bottom holes in the lifter are uncovered. All measurements in the oil galley area are rather crude as we are measuring against as cast surfaces. However the difference in the diameter of the cam heel is .080 so a inaccuracy of a few thousands should not matter. The dimension from the bottom of the lifter to the bottom oil hole does show a great variation from lifter to lifter.
Like you, I am reluctant to drop the sump, so I think I have a plan.
As you know, the tappets are cast, chilled iron, and while the sides, top and bottom are machine-finished, the holes are rough-finished.
So I am going to purchase a new set of tappets and drill each pair of holes using a crib to the same radius as the tapped diameter (so as to hold them firmly) and drill each one out on a drill press, to the full hole size, and then make sure that there are no rough edges. In fact I may even elongate the holes on the bottom of the bottom pair and on the top of the top pair but I haven't figured out yet, exactly how to best accomplish this.
The thought of my cam lobes running dry is not appealing!
|Gordon A. Clark|
When you have your tappets out have your machinist run a line down the side from hole to hole to the face of the tappet about 1/16" wide by .030 deep, i.e., there will be four lines down the outside of each tappet for oil to flow down. This will ensure there's oil on the tappet/cam face. This was shown in the George/Peter Edney XPAG engine rebuild video and is kind of mentioned (but not explained) in the Sacred Octagon article (I think he mentions something about someone filing flats on the side of the tappets - can't remember since it's been a while since I read the article). If you're not following my explanation contact me offline and I'll email you a photo.
I didn't pick that up from the article when I first read it, but I believe you're right.
This is a good idea, as it also presents the opportunity to match them by weight by the amount of material one removes in (making either) the groves or flat spots.
The difference between old and new clearances is .08 and this could be significant enough to block the oil hole, so I'm inclined to like the idea of scribing the sides
|Gordon A. Clark|
I think you have a lot of us at a disadvantage, as we don't have access to the article you are talking about. I will be starting a rebuild very soon which will include a cam and followers.
Where can I get a copy of the article?
|N S Miller|
"This is a good idea, as it also presents the opportunity to match them by weight by the amount of material one removes in (making either) the groves or flat spots"
Since these are not reciprocating parts with the crank, rods, piston assembly would balancing have any merit at all?
Put the top down on the TF yesterday due to a big warm front that'll be around for a while. Oh how nice it is!
|Well, the valve gear does actually reciprocate, but at half the rpm of the pistons/crank. And since the travel of the tappets is so short, the linear speed is pretty small relative to the pistons. I don't really know the impact of balancing the valve gear, but it seems that it would have a negligible impact, unless you were building a race engine and wanted to wring the last bit of RPMs out of the engine. |
But now I'm going to have to weigh my tappets when I do my rebuild this summer, just to see how close they are.
The article was in the December issue of "The Sacred Octagon" which is the bimonthly journal of the "New England T Register" in the US. Unfortunately the issue is copyright so cannot copy to the board. However the basis for the problem is the change in the base circle diameter of some new cams that are being sold today vs the original design of the cam. The original cam had a base circle of 24.5mm while the new cams seem to have a base circle of 28.5mm (about 0.080 in difference). The design of the XPAG used the hollow cam lifter (tappets) to allow oil to lubricate the cam lobe when the lifter was on the base circle of the cam. However due to the change in the base circle, the lifter may not uncover the lower holes so that the oil can flow to the cam as it is 0.080 higher in the engine block.
Before modifying the lifter, I would suggest measuring the distance from the lifter galley to the base circle of your cam. I made a tool for the measurement but you can get a good estimate of the problem by setting the cam so that the lifter is at its lowest point and marking the lifter with a pencil at the height of the galley (on mine the mark was slightly above the upper hole in the lifter) and then measuring down the thickness of the block to see if the lower holes are exposed. Jim measured 1.28 in as the block thickness. Performing these measurements on my engine with a new Abingdon Spares 0.012 cam showed the lower holes were open to the cam. The lifter is hardened so a drill will have a problem opening the holes in the lifter. I was able to open them up with a 1/3 hp die grinder using a diamond wheel.
|I sure don't want to disassemble my freshly rebuilt engine, but now I'm worried. I've got the moss (crane) cam with new lifters. It hasn't been started yet. I'm thinking about the following test, let me know if you think it will work:|
If I remove the tappet cover and fill the exposed upper lifter hole with oil, then crank the motor through a full combustion cycle by hand, the lifter should drain if the lower hole opens. If the lifter completes the cycle and remains full, its got the problem.
What do you think?
PS. I'm not going to test this until I'm ready to strt the engine, as I don't want the oil to wash the assembly lube off of the cam and lifters yet.
|Evan Ford - TD 27621|
Your method should give you an indication of the problem. If you are dissembled to the point to make your test you are only a valve cover and rocker assembly away from removing the lifter and making the measurement if the results of your test are not conclusive. I do not know if you have seen the article, but it was a Moss/Crane cam that caused the original investigation by Jim Finne.
Not sure if you bought your tappets recently but there have been a large amount of bad ones in the past. Moss has now started quality checking them and having them heat treated. I had an information sheet that I received from Moss posted at: http://www.mg-tabc.org/techn-up/tappets.htm .
I suggest you read it and if you didn't get this with your tappets that you contact Moss and see if they will exchange your tappets for a new set. Why take a chance on your new cam?
I also suggest you have a machinist grind some oil grooves in the tappets. It's inexpensive insurance that will ensure oil is reaching the face of the tappet.
|Thanks Gene and Janson,|
I'm guessing I've got the suspect tappets. I purchased them during my dissasembly back in late 98. They had a different part number then (433-368). The new part number is 433-366. I'm sure the set didn't have a dot on the face.
I had better call Moss.
|Evan Ford - TD 27621|
Many thanks for your valued input. I had forgotten about the case-hardening on the lifters. I will have to source a diamond router of the appropriate size.
I'm not going to remove my 2-year-old rebulld from my TF as I just don't feel like it.
I think, that once I get the tappet chest exposed, I will have a better idea. Trying to examine the tappet chest on a TF is not easy especially for my vintage eyes, however, I think that if I had a lobe running dry, I would know about it by now, but to play it safe, I think I will devise some way to get a magnet throught the sump fill hole to check for any metal filings, ets.
In the meantime, I plan to proceed with my plans to make a new, back-up set, suitably improved.
|Gordon A. Clark|
Regarding the magnet through the sump drain, here is another idea. Heavy equipment users and aircraft owners have their oil analyzed frequently. Some at every change. Stop by your local airport using airport transfers tonbridge (for small private planes) and talk to their mechanic. He can point you to people who offer the service. A pint of drain oil will get you a very detailed analysis of what is happening in your sump and the overall condition of your engine.
|J. M. Haskins|
|I received a response from Michael Grant of MOSS motors. Here is the text from a prepared letter with Moss, Cars, and Nisonger letterhead:|
440 Rutherford Street
Goleta, CA 93117
805-769-7234 Direct Line
To: Customers with 433-368 Tappet Sets (433-350 Tappets)
Date: Monday, March 15, 2004
Re: T series Tappets
A characteristic of the T- Series engine is the relatively short life of the tappets. This has been the case since the cars were new. There are engines that don’t seem to have a specific problem, the tappets just wear out. The same tappets in other engines last longer for no apparent reason. The tappets we have sold for years are the same tappets sold by most distributors. They were made to OE specifications, and have been used successfully by engine rebuilders all over the world. Some specialists developed procedures to address the problem (or problems) they felt contributed to short tappet life. Moss launched a thorough investigation to see what could be done to improve the tappets we offer for the engine. We found the following to be factors affecting the life of the tappets:
· Size, especially Outside Diameter
· Matching the Tappet to the Cam
· Surface Treatment, especially Parkerizing
· Break-In Procedure
We have decided to offer the best tappet we can by addressing these issues. The 433-368 Tappet Sets Moss has offered for years have been used by shops and individuals hove worked as well as any tappet sold for the T-Series. The characteristic T-Series problems of short-lived tappets have been attributed to a number of factors. We are convinced that there is no single factor to blame; it is a combination of factors. There are a number of steps that can be taken to maximize the life of a T-Series tappet, and these have been incorporated into the
433-366 Tappet Set.
We have the tappets we use inspected by Elgin Cams. The outside diameter is checked against factory specification, which calls for an OD of 0.9049" to 0.9065". Elgin checks the outside diameter in four places along the length of the tappet, offset 180 degrees from each other.
Elgin also checks the hardness of the tappets. Anything less that Rockwell Hardness 54 on the C scale is not used.
We sell Crane Cams for the T-Type, and the lobes of the Crane cam are tapered (higher by 0.0011” on one side of the lobe) to promote tappet rotation, which is essential to long tappet life.
To promote tappet rotation, we have the tappets “crowned”, which rounds the surface of the tappet slightly to better match the cam lobe.
The surface of the tappet is then polished to restore the fine finish after crowning. The tappets are then Parkerized, a phosphate etch process. Typically producing a light to medium gray finish, the final finish color will vary based on the phosphate compounds used. The finish holds oil well, which is exactly what you want.
And finally, break in is a factor. The perfect tappet will be ruined if not properly broken in. While we cannot control this critical process, we include the information we have gathered from the experts with the 433-366 tappet set.
The article that appeared in the December 2003 “The Sacred Octagon” (TSO) has sparked a lively discussion on tappet lubrication. The gist of it is that the oil flows from the head assembly into the block and over the camshaft through the holes in the sides of the lifter. The base circle of the Crane cam is larger than the stock cam, and this keeps the lifters higher in the lifter bores, which in turn keeps the oil holes in the sides of the tappet covered by the walls of the lifter bore - reducing the oil flow to the lobes of the cam.
This could very well be a major contributing factor to the reputation of the T-series tappet problem, though we must again state that this is probably not the only factor. It is clear to us that there has been a general quality problem with tappet manufacturers for some time.
We are determined to get to the bottom of this problem and have shared the TSO article with Crane, Elgin and a number of T-Series specialists. While there is not 100% agreement, all agree with the premise of the article in that anything that improves the oil flow to the cam will help and certainly not hurt.
We have asked Elgin to investigate what needs to be done to incorporate this modification and when available it will be included in the 433-366 tappet set. In the meantime, there is nothing to keep an individual from elongating the holes in the tappets with a Dremel or other suitable grinder.
|Evan Ford - TD 27621|
|Today we pulled the lifters on a TD engine rebuilt about 4 years ago, probably 4K miles on it, with the "fat" Crane cam, not sure if the lifters were from Moss or Abingdon. All 8 were absolutely perfect, with evidence of normal rotation. We left all alone, and reassembled. This very well could be a multi-factor problem as discussed above, that happens on only some engines (casting core/cam bearing bore shift, lifter quality, etc).|
|I hvae had the Moss lifters in my car for 5400 miles and no problems so far. The manufacturer of my cam is unknown as it was in the car when I purchased it. My engine runs very well and so far no problems. I do know of others that have had some problems with the lifters but mine are fine.|
This thread was discussed between 07/03/2004 and 27/03/2004
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