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MG TD TF 1500 - Aluminium Tappet Cover
|I have a slab of aluminium and am considering machining a tappet cover. I think the ones available from the usual suppliers look a bit "naff". I propose to fabricate a flat one with ribs and raised octagons around the fixing holes. Is there a reason for the original steel cover to be domed and will a flat one be OK? Also is a breather necessary? Will the engine not vent via the rocker cover?|
|I would think the original is domed for stiffness and/or to prevent it to act as a drum?|
If a breather is necessary I don't know, but thinking about it maybe there are two holes to create a circuit? The rocker cover being the way out and the tappet cover the way in?
I've always liked my tappet cover; I've never seen another one 'in the flesh'.
|Willem van der Veer|
There have been a number of threads regarding pressure in the engine causing oil leaks and how/why to relieve it. Mort has had issues with an overpressure situation and maybe he can shed some light on the subject. I have an aftermarket tappet cover that has two breather ports with an MG crest on each.
|I think the cover is domed for stiffness as said above, but also for venting and the prevention of liquid oil entering the vent. The cork gasket underneath unusually covers the full area of the cover, but for a couple of holes. This and the air gap to the vented cover prevents liquid oil entering the vent. Its also a cheap way of making a cover.|
An alloy cover has to be stiffer and seal better, so iI wouldn't mind one myself, if I can find a good one. The type shown above looks ideal.
The vent through the rocker cover alone might be OK, but a bit restricted.
|The coffin valve covers were (are?) pretty square but they are cast|
|I had an aftermarket side cover which I removed and replaced with a Wolseley 4/44 side cover which has an integrated flame trap. This when connected via a PCV valve and a restrictor to the inlet manifold forms a closed circuit breathing arrangement. Every other source of infiltration air being sequentially blocked off forces the engine to draw in some air through the rear crankshaft scroll.This arrangement helps to reduce the oil leak as where air is drawn in oil can't flow out (in theory anyway). It took a lot of experimenting to set up but the result was from a torrent to a trickle.|
|The Wolseley side cover during the experimental stage and a Land rover flame trap which has since been removed.|
The down side is that it upsets the idle.
|Photo didn't upload.
Why is the tickover compromised? Does the positive pressure from the crank case act as a mini supercharger and force air past the closed throttles?
I ran the TF's engine without air cleaners whilst balancing the carbs and found oil dripping from the breather tube in the rocker cover. This wasn't caused by pressure but was simply splash. I don't have the original pipe that joins the rocker cover to the air cleaner of the front carb. I believe it should have some sort of trap for splashed oil. I have simply bent my pipe so it exits the rocker cover in an upward direction in the hope oil will trickle back. It appears to work.
Isn't Willem's tappet cover the best! I am going to machine a copy from billet aluminium. Only problem is milling the internal corners of the octagon and "MG". I got round this when I made a gear box cover for my prewar MG by cutting/filing the octagon and letters from sheet aluminium and sticking them to the cover with epoxy. I suspect with oil and heat they would soon fall off a tappet cover. Mill rounded internal corners with a fine cutter and finish off with a small chisel? Any ideas?
|It would be a lot easier to machine a circular base and fit a bolt on MG radiator badge.|
Good idea but I think maybe one of the badges from the center of the hub caps? Will look out for one at the NEC Classic Car Show in three weeks time.
Just measure to make sure the the thickness of the cover plus the thickness of the gasket will not interfere with the dizzy. You can see in the pic that Delcan posted that the fins are cut back so as not to interfere.
|As Jan toted, the Hubcaps are ideal,|
I made a steering wheel center for my TD.
I was looking at making the MG Logo on the Mill. Its Mostly straight lines. But as you noted the Inside corners are an Issue.
I di purchase a very small (1/32" I think) end mill but then decided on the wheel covers.
I had already used them on the gear shifter knob.
Using the stub on the inside, I held them in a collet and turned the OD round.
I then used Locktight to anchor them in to the Knob and the wheel center.
I have attached a composit picture.
Top frame is a commercial unit.
Steering wheel hub in the middle
Hub and shift knob in the bottom.
I still haven't figured out exactly why the idle is affected. I found that fitting 1.7mm restrictors between the PCV valve and the inlet manifold did help. The idle is not erratic-just too high when warm. It could however be a carb issue e.g. worn throttle spindles.
Have your carb bodies been rebushed? The ends of new bushes are square and they need to be pressed in so they protude into the choke tubes and then rounded off. If you don't do this there is a small gap when the butterflies are closed and you cannot get a slow tickover.
|Better still if you machine the carb bodies just deep enough to take the bushes pushed in from the outside, leaving a small solid stop on the inside. That is if using the bushes provided by Burlen. If doing it again I would make my own with a flange on the outside and finish them flush inside.|
|The coffin covers are readily available including logo flip cap, at a reasonable price and are sand cast as original so they look correct. Making one from scratch would be a lot of work!|
|Thanks Jan and Dave,|
Do you know to what tolerance homemade bushes would need to be reamed? H7??
Yes I have seen aluminium rocker and tappet covers for sale but now that the TF is completed I am looking for something to do! I don't really have room for a second classic car and don't want to sell the TF so some fabrication work would be welcome. I suspect other, retired owners will sympathise.
It is amazing how these threads drift. What stared out as a query on tappet covers is now discussing carb spindle bushing but that's the beauty of this site. I have wondered why oversized spindles are not available. Surely these wear as well as the bushes. To cut stopped holes in the carb body and get them to line up would be difficult. Better to line ream them from one side in a single operation. I suppose thick bushes could be pressed in and these could be line reamed but there would still be clearance between the spindle and the bit of the carb body that had not been opened out. Whether tis would affect tickover I Don'know. To cut stopped holes would also need a machine.
over size spindles are available. At least they were 15 years ago as I overhauled my carbs then.
It was before I retired and still had access to machine tools.
Ray TF 2884
|If you're that bored, you can fly over here. I have plenty of old car projects you can spend your time on. :)|
|Sorter trip to come here Jan and help me out :)|
This thread was discussed between 20/10/2016 and 23/10/2016
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