The MGA With An Attitude
Broken ALLOY SPRING CAPS for engine valves -- FT-003

broken alloy valve spring caps on engine Part: Alloy spring cap 460-305 Supplier: Moss Motors, Ltd. Purchased: May 2000 In Service: Oct 28, 2000 - 59,893 mi Failed: July 6, 2003 - 82,923 mi Service life: 23,030 miles

broken alloy valve spring caps Top side. broken alloy valve spring caps Bottom side.

Pictured above we have top and bottom views of of two failed alloy valve spring caps, Moss part number 460-305. These parts are designed to be used with the later model valves with round keeper grooves and cotters to match, 1968 and later MGB parts. You may also review the description in the Moss catalog, especially this part: "Caps weigh aproximately 50% less than the stock caps, and are much stronger".

I can tell you without reservation that these parts are definitely not stronger than the original steel parts, and in this case hardly even strong enough to serve the intended purpose. These parts also have a considerable inconsistency in manufacture, which ultimately lead to the failure.

The outer edge of these parts, the step that retains the outer valve spring, is very thin, which is why and where the parts broke. Of the 8 parts installed, 4 of them had an outer lip about 1/8 inch thick. These 2 parts in the picture had an outer lip less than or equal to 1/32 inch thick at the outer edge, and not much thicker at the ID of the outer spring. The other two were somewhere in between, but one of those is not much thicker than these, and I am concerned that it to may suffer the same demise in due time. I did notice this variation in the dimensions of these parts during assembly. But since the catalog touted these parts as being "much stronger" than original parts, I was lulled into believing they might be okay, and went ahead with the installation.

Upon inspection after failure, it is fairly obvious that the metal alloy is also quite soft and subject to rapid wear. In the second picture, looking at the underside of the part on the right, you can see deep wear marks where top ends of both the inner and outer valve springs were cutting into the soft alloy. Both parts also have substantial wear on the cylindrical surface of the larger pilot diameter, to the point of being noticeably wasp waisted. I don't know if these parts were erroneously made of a soft alloy and/or may have missed a heat treatment step in process. But in any case, the metal is definitely too soft to hold up in long term service. It is fairly easy to cut a sliver off the edge of these soft aluminum parts with a sharp pocket knife. I am recommending to Moss that they should review current inventory to see if this part number 460-305 still has these same problems.

side view, thick, thin, broken
Correct part on left - - Thin edge part in center - - Broken part on right

These parts may or may not be representative of similar parts currently in stock, as these were purchased in May 2000. If current parts are better quality and up to the advertised values of "much stronger", I might consider replacing the whole set with new ones. If current parts are still made of the same soft metal, I will graciously pass and reinstall a full set of original steel spring caps. A momentary 7500 rpm may be nice for a race car, but it's not nearly as important as long term reliability for a street machine. Even if these parts were all made to the correct dimensions, I think they would have serious wear problems within 50,000 miles of normal street driving.

If Moss has done a known update on these parts recently, or if there should be any news after inspection of inventory, I would appreciate some feedback.
Addendum Sep 15, 2003:
I just got a report late tonight at our local club meeting of another failure of these parts. David Bralich (who incidentally runs an MGB in vintage racing) just had the same type failure of one of these same aluminum spring caps on his daily driver MGB. That car has an aluminum cross flow head, and we are all very concerned that these parts failures should not start destroying such valuable commodities. No word on the condition of the head yet, except that it did drive home with some noticeable increase in valve noise. We will be having a club tech session to investigate this one within the next few weeks, at which time I will likely get some more pictures of the failed part(s).
Addendum Sep 29, 2003:
Just finished posting pictures and notes on the Dave Bralich MGB valve spring cap failure.
Check here:

I'm still waiting for feedback from Moss before I dare to buy more of these parts for replacements, or recommend them to friends again.
Addendum Feb 13, 2004:
After additional correspondence and prompting, as of today Moss Motors states that they agree that these parts are not made consistnetly, that they have frozen current inventory, and that they will not sell any more of these parts until they can do 100% inspection of the existing parts. No word on whether they intend to attempt to contact past purchasers of these parts, so I advise anyone who may have any of these parts in their posession to check their parts. If they have been installed in an engine, this would require lifting the valve cover for inspection.
Addendum May 10, 2004:
Found another source for these parts. They may be purchased from Pierce Manifolds.
P/N 12H3309-8 for a set of 8 pieces.
P/N 12H3309 for a single piece.
6061-T6 aluminum, NC machined, very nice consistency.
As a matter of convenience, I bought a few pieces through
"Kai M. Radicke" <>
Thanks Kai.

Thank you for your comments -- Send e-mail to <Barney Gaylord>
© 2003-2004 Barney Gaylord -- Copyright and reprint information