Rhodri Posted December 17, 2007 Report Share Posted December 17, 2007 (edited) My TR4 has a chrome rocker cover that has two holes on top, one near each end, for the studs to come through to bolt it to the head. All the other ones I had seen were like this. However, I looked on the autojumble bit of Rimmers site and they have a cover for sale that has another hole, in between the two stud holes. I looked through a few books and found a picture of another one that appears to have a brass bolt in it? What is this hole for? I assume that the engine "breathes" through the filler cap, or through the outlet pipe on the later covers, as well as any crankcase vent. Edited December 17, 2007 by Rhodri Quote Link to post Share on other sites
ianc Posted December 17, 2007 Report Share Posted December 17, 2007 I think the centre hole is to permit connection of a pipe feeding fumes into the inlet manifold, such as is done on the TR4A. The more usual arrangement on the 4A is a metal pipe exiting at a 45 degree angle towards the carbs, and a filler cap which provides a seal (rather than a breather). Perhaps this is an attempt to provide a retro-fit solution on TR4s? My advice would be to plug the centre hole and let the cover breath in the old-fashioned way, as that gets rid of water vapour from the oil and means that the inside of your rocker cover will be oily, not covered in the emulsion which so often results from modern extraction systems. Ian Cornish Quote Link to post Share on other sites
Trevor S Posted December 18, 2007 Report Share Posted December 18, 2007 (edited) I'm sure Ian is probably right as I can see no other reason for it. However rocker covers with the hole and brass bolt are not uncommon. My ex US 1962 TR4 fitted with SUs had one prior to being restored, and the cover I replaced it with from another TR4 engine, as it had better condition chrome, also has one. The engine is the original one for the car but clearly there is no guarantee that the rocker cover was. The hole seems in a strange position however for the purpose Ian mentions unless there was a 90 degree threaded pipe to fit it. The 45 degree pipe seen on 4As mentioned by Ian was just for a push on rubber pipe with no thread. I have never seen such a hole on a sidescreen rocker cover. The hole in the 2 covers I have certainly appear to have been manufactured like that and do not appear to have been added later. I have never seen a TR however making use of this hole for the purpose mentioned by Ian, or any other use for that matter. Is it possible that this is another parts bin item that was also used on another contemporary Triumph? I can't personally think of one that springs to mind which was a similar shape and which was also chromed. Trevor. Edited December 18, 2007 by Trevor S Quote Link to post Share on other sites
Rhodri Posted December 18, 2007 Author Report Share Posted December 18, 2007 Thank you Ian and Trevor. I agree Trevor that the hole appears to be a factory mod and not a homemade job, and , as Ian says, may well have been to get rid of fumes, but it looks too elaborate for that- the plot thickens! Quote Link to post Share on other sites
bob-menhennett Posted December 18, 2007 Report Share Posted December 18, 2007 Rhodri There are pictures of the brass nut on the cental hole in both the Workshop Manual ( clearly an "earlier" model ) and Bill Piggott's book Orginal Triumph TR4/6 but......sadly no reference as to it's purpose. My money is with the others....some sort of breathing/emissions experiment / set up that didn't proceed...hence a blanking brass nut. Bob Quote Link to post Share on other sites
Rhodri Posted December 18, 2007 Author Report Share Posted December 18, 2007 Well, I needed an early cover so I bought it yesterday and it arrived here today- first class service! The boss is a factory job with neat welding and it has then been chromed.I also saw the pics in Bill Piggott's book, but I have a later manual. Next job is to find a brass bolt, or better still, the reason for the boss! Quote Link to post Share on other sites
Smokey Posted December 20, 2007 Report Share Posted December 20, 2007 The TR4 had three types of rocker covers. The first was identical to the TR3, except the oil filler cap was at the rear rather than at the front, and this was used up to engine CT1422E. From CT1423E to CT23594E, the rocker cover was fitted with an insert for a closed ventilation system that was used on another car, presumably the Vanguard, that used that recirculating breather system. The TR4 continued with the crankcase vent, so a brass plug was inserted in the hole in the rocker cover. After engine CT23594E, the TR4 also went to the closed breather, lost the crankcase vent, and got the tube on the rocker cover leading to the flame trap and then into the carburetors. This is documented in the Triumph Register of America Concours Guide for the TR4, and is also shown in the TR4 parts manual. So all engines from CT1423E up to CT23594 have that brass plug. Quote Link to post Share on other sites
Rhodri Posted December 20, 2007 Author Report Share Posted December 20, 2007 Thank you! The mystery is solved and with an engine no of CT 17022 E, I have, coincidentally, bought the right rocker cover. Quote Link to post Share on other sites
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