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MG TD TF 1500 - Camshaft character experience
|NTG (www.mgbits.com) offers a camshaft with for me remarkable properties. Its degrees are 52-18-18-52 which makes a pretty large overlap of 36 degrees. Also the announced lobe separation angle of 107 degrees in my opinion would mark its character as not so standard. |
Anybody out here experience with this camshaft: does it deliver at the higher rev's and what about the low rev behavior (rough or still ok).
|Huib, Please contact me off the BBS for flat lifter & roller lifter camshaft information.|
I have this camshaft in my engine since 3 years. I'm very satisfied with it. Idle is very good and top speed also.The lift is not so high as the original.Instead of valve clearance 0,21 Inch I do it with 0,12.
You didn't mention your application, street, high performance or supercharged.
Just a comment... if it is supercharged, which I realize is probably unlikely, avoid a cam with wide overlap. I picked up one of Len's cams for street supercharged with minimal overlap. I should get around to ordering a second one since we have 2 supercharged TDs.
|Len, you have got mail.|
Klaus, if the clearance is decreased from 0.021 to .012, the overlap gets increased above the 38 degrees. I find it remarkable that idle is still very good.
Jim, I can understand that the high inlet pressure at supercharged will blow straight away through the outletvalve during the long overlap.
|Huib there's an article in the archive called "Valve Springs for Roller Lifters" that you should read if considering the roller cam kit. Cheers|
Peter TD 5801
|Huib, oops email@example.com|
|Neil Cairns has published some info on the variety of standard cams fitted to M.G.'s over the years on pages 25 & 26 of his book "Engines for M.G.'s". I've reprinted the following.|
"XPAG Camshaft Checking.
This is the most important part of the engine in terms of performance and drive-ability, though good cylinder head design does help. As years pass, people modify their cars, or fit replacement items that have been improved by the manufacturer. One problem that often occurs is trying to decide which camshaft your XPAG has fitted, without stripping it down. Many cars have the 0.012" clearance camshaft, but some still have the older 0.019" clearance version. By far the best method I have seen was in the MGCC Safety Fast magazine, sent in by David Clark of Westminster, Vermont, USA. It relies on the fact that only the later cars had 5;45;45;5 cam timing, known as equal-overlap, or split-overlap if you speak American. That is both inlet and exhaust cam have the same timing, but in 'mirror' fashion. The earlier 'T' types had 11;57;52;24, very un-equal. The first pair of numbers read as inlet opens BTDC, closes ABDC, then exhaust opens BBDC and closes ATDC. The XPAG is not a quiet engine anyway, and one to worry about is one with no tappet clatter, as it is better to hear it than not. In todays lead-free petrol age, no noise means the valves are pocketing, ie eating away the seats, and closing up the clearance.
If David Clark's check is carried out, and you decide you have a 12 thou cam, but performance is awful, you actually have one of the mid-way 5;45;45;5 1140cc timed and ground camshafts, but with an 8mm lift at the valve for the M.G. 1250cc XPAG. See modification list. This cam still has a 0.019" tappet clearance. Conversely, running a 0.012" cam at the 0.019" clearances sounds almost like a diesel engine.
" I would like to share with you a cheap and cheerful method for making an accurate determination of high verses low camshaft with your feeler gauge, a screwdriver, and a five-sixthteenths BSF spanner.
Because of the equal overlap of the valve timing, of the 0.012" clearance XPAG 5;45;45;5, they are split evenly about top-dead-centre ( TDC ) and bottom-dead-centre ( BDC ). This is called split-overlap.
Now, to check the valve timing, adjust the valves to the recommended valve clearance, in this case 0.012". Turn the engine on the starting handle until the fan belt pulley on the engine indicates TDC for number one cylinder, with the valves ROCKING. This means we are at the end of the exhaust stroke and beginning of the inlet stroke, with both valves partially open. At this TDC loosen the locknuts and turn the tappet adjusting screws all the way up and then down again until there is exactly no clearance at the valve. The valve will now be shut, and the adjusting screw just touching it. Now turn the engine one more crankshaft revolution ONLY, ( till you are now at the top of the compression stroke,) turn until the TDC marks on the pulley once again align exactly. Using your feeler gauges measure the resulting valve clearance. If the clearances match, you have a split-overlap camshaft, possibly with 0.012" design. If you are out five to ten thou, with the differences being from keyway tolerances, etc, it is still a split-overlap cam. If it is an earlier, or fast cam, the clearances will differ a lot."
Camshaft lobe design is a very precise art, and the shape is very important. Morris & M.G. strove to get the best with silence, but a compromise was the result. The .012" gap was it. The gap is part of the camshafts design and has to do with the 'ramp' and its acceleration of the valve lifting gear. Stick to the clearances given.
Model Cam Timings Lift Part No, ( if known.) .
SA 2 ltr Saloon, 11;59;56;24 8mm
VA 1 1/2ltr Saloon, 11;59;56;24 8.4mm (later 11;57;52;24)
WA 2.6 ltr Saloon, 11;59;56;24 8mm
1147cc 10hp engine 5;45;45;5 6.5mm
TA midget, 11;59;56;24 8mm X24084, MG862/171, AAA5776.
TB & TC Midget, 11;57;52;24 8mm MG862/171, X24084, AAA5576.
TD Midget & YT 11;57;52;24 8mm MG862/171,168552, AAA3096.
TD after TD2/24116 5;45;45;5 8.3mm AAA3096, 168553.
YA 1 1/4ltr Saloon 11;57;52;24 6.5mm MG900/106.
YA after SC/16831 5;45;45;5 8.3mm AAA3096, 168553.
YB 1 1/4 ltr Saloon 5;45;45;5 8.3mm AAA3096, 168553.
TF 1250 & 1500 5;45;45;5 8.3mm MG862/171, AAA3096, 168553.
Wolseley 4/44 5;45;45;5 8.3mm AAA3096, 168553.
half-race; 13;59;50;22-8.3mm, AEG122, full race; 32;58;60;30-8.3mm AAA3095 .
The XPAG engine was also fitted by other sports car builders, in tiny quantities. People like Cooper and Lotus put them into their specialist cars, and of course it went racing in many forms, being capable of quite some development. Considering the engine was an improvement of an old Morris sv unit, the MPJM, in the Morris Ten series 'M', the XPJM 1140cc 10hp version with just 37bhp, then being uprated for M.G. to 1250cc with either 46bhp or 54bhp, it is amazing to think that Syd Enever, MG's chief designer, obtained 213bhp at 7000rpm with a supercharged version, pushing a car up to 210mph, from the same simple XPAG! Outside specialists often offer tuning equipment for sports car engines, and today the cross-flow alloy head for the 1798cc 'B' series is on offer by Webcon Ltd in Middlesex giving 120bhp. In the 1950's people like Laystall also offered an alloy cylinder head for the XPAG, with polished larger ports and balanced combustion chambers. More information of this type is in 'Tuning and Maintaining MG's', by Phillip H. Smith, Haynes."
Hope this info helps you make an informed decision Huib about your choice of cam. Cheers
Peter TD 5801
|Thanks for that, Peter. |
When Neil says:
"At this TDC loosen the locknuts and turn the tappet adjusting screws all the way up and then down again until there is exactly no clearance at the valve."
I am assuming he meant 'valves' for that last word... i.e. you are supposed to adjust BOTH the intake AND exhaust valves for #1 cylinder such that there is no clearance and the valves are fully closed.
|Dunno Kevin. I haven't got an original unknown cam in my TD so I didn't need to go down that road. Just checked the valve timing on my Chet Herbert cam with info provided by the manufacturer (Andrews Products) & I'm relieved to find that it's near enough to spot on. Exhaust is 036" @ TDC & Inlet is .050" @ TDC (Should be .052" which is close enough for me). Sorry I can't answer your query but I'm sure somebody here will. Cheers|
Peter TD 5801
|Chet Herbert has not produced a MG camshaft since about 1962. You do not have a Chet Herbert cam.|
|That's surely in part due to the fact that Chet Herbert is no longer alive. His son Doug now runs the business.|
|Thank you Peter for that interesting overview. Also "David Dubois" presented in the past camshaft info that is published on our famous TTalkinfo (http://www.ttalk.info/TSeriesCams.htm). |
Combining that info and only listing a few, demonstrates my initial question:
Early TD and TC cams: 11-57-52-24 makes overlap 35
Late TD and TF cams: 5-45-45-5 makes overlap 10
Half race cams: 13-59-50-22 makes overlap 35
Full race cams: 32-58-60-30 makes overlap 62
Current offered MOSS standard cam (also Crane 340-0002):
11-51-51-11 makes overlap 22
Current offered NTG cam: 18-52-52-18 makes overlap 36
Only looking at these figures,makes me conclude that the early TD/TC cam and the later Half race cam are kind of lookalike.
And: The late TD shows much less overlap so further away from the full race and half race area into the none race area.
The MOSSstd is between the late TD and half race (so between none-race and half race).
The NTG is between the MOSS and the half race.
Agree/disagree with this reasoning?
So, back again to my initial question: who (else than Klaus) has experience with this NTG camshaft?
This thread was discussed between 24/01/2015 and 26/01/2015
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