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MG MGB Technical - MGB Camshafts

Hello, Can someone recommend a suitable camshaft for a 1967 MGB, 9.5:1 CR, 1868cc C/iron manifold, Falcon Exhaust. After reading all the hype I mistakenly fitted a Piper 270 which has totally ruined the car. We do regularity road rallies where you need to keep a speed of 28-32 mph up. I now cannot get smooth running anywhere near 30 mph, the car hunts backwards and forwards which is not improving the G/box or B/axle. I would like a cam to give smooth running from 1000 rpm.
Any ideas anyone please?
Graham
G Cherry

Of interest did you;
1) time the cam in using timing disc and dial gauge.
2) rolling road tune the car after cam fitted?

What you describe sounds like very weak mixture/misfire.

The 270 Pipers are really sweet and the factory could have fitted them and everyone would have been happy with the power band. A properly set up 270 cammed engine on SUs is super smooth even at idle.
Peter
Peter Burgess Tuning

Hi Peter,
The engine was rebuilt by Steve at EngineTech, the old Don Loughlin place, with a BP270 cam set to 107 deg. 1.1/2 SU's, needles 6, K&N filters. It's not been rolling road tuned and has now done around 9000 miles since rebuild in 2013.

Graham
G Cherry

I think you need to get it on the rollers Graham and see if it can be improved.
As the cam is symmetrical timing a quick check for timing is to get say number 1 in and ex valve on the rock and move the engine back and forth until the lift on them is about the same, look at the timing mark and see if it as TDC or how near to it.

Peter
Peter Burgess Tuning

Graham, you can't be many dozens of miles from Peter in Alfreton. It would be money very well spent to take the car to him and get it properly sorted. There's no-one better with MGBs.
Mike Howlett

Hi Peter & Mike

I guess that's the only way to sort it properly, I'll try and check the timing as you recommend Peter to see if it's close to TDC and then give you a call to arrange a visit. I'm rebuilding the front hubs and brakes at present so it may be a few weeks before I'm mobile.

Cheers
Graham
G Cherry

I would be happy to see if we can sort it Graham.
Peter
Peter Burgess Tuning

I agree completely with Peter - that cam should not be grumpy at all, so if it's not running right it will be down to set-up. Although there are sometimes exceptions, in general if you change the tune of an engine then the jetting and ignition settings developed by the manbufacturers for a standard engine will no longer be relevant. Sometimes the difference is small and the engine runs reasonably well on std settings but would go usefully better if set up properly. On others, the standard settings are nowhere near the mark.

A couple of examples:
We recently had a B in for which we'd supplied a fast road camshaft several years and owners back. This particular camshaft usually works well on the standard timing and jetting in an engine with a modified head, but in this case it did not.

As I didn't put the engine together I'm not privy to exactly what else was done other than it being 1950cc, a useful amount of head work and the compression appeared to be up quite a bit more than normal.

In summary, what appeared to be lumpiness from the cam profile complete with bottom end gasp was in fact overfuelling and a big rich flat spot. (Higher compressions and more capacity can draw more fuel) With the correct needle profile it was a completely different car: slightly waffly idle but smooth everywhere else and pulled cleanly from all engine speeds.

Currently we have the same exercise with a TF1500: rebuilt engine with a modified camshaft but most else standard including compressionr ratio. This one was too rich at idle, too lean on cruise and way too rich on full throttle, so quite a different needle profile is required once again.

Apart from the benefits of having the car run smoothly, good RR session often provides the cheapest BHP available, so is well worth the cost.


Paul Walbran

Quite right about tiny problems causing massive effects Paul, we had a B in recently so bad I thought the cam was a tooth out. It turned out tappets were 10 thou and when set to 20 the car was transformed and really sweet everywhere.
Peter
Peter Burgess Tuning

Thanks Peter, I'll be in touch as soon as I'm mobile again.

Graham
G Cherry

We have a Piper BP270 in our 1380 A-Series engine and it runs very smoothly a low revs, with a good idle at ~1,100rpm. 4th gear is almost 18mph/1000rpm and 30 mph is very easy indeed (~1,700rpm), even in 5th at 21/1000 is no real problem!

In a bigger 'B' Series engine I would expect it to be almost OEM smoothness standard.

With both a Kent 276 and Piper BP270, the low speed smoothness has never been a real problem, but the idle has really improved after fitting a 3D mappable ignition unit - the NODIZ. With the NODIZ the advance at idle can be increased significantly, and that really does smooth the idle and low speed response.

The Kent 276 and the Piper BP270 originally were both fitted 4° advanced, and had no obvious 'caminess'. After rebuilding the engine 2 years ago I timed the Piper BP270 'straight up', and since then have noticed a slight 'off the cam' until ~3000rpm. If I need to take the engine apart in the future, I would put the cam timing back to 4° advanced.

As a general rule, more cam advance = more lower down torque, less higher up power and with cam retard it is the opposite.

Richard
Richard Wale

I also had a 270 cam. Timing in is essential, as is running it in properly for the first 15 mins after start up. Also they have wider thanstankard MGB valve clearances. I always set them when the valves are "rocking", not the rule of nine.
Allan Reeling

Hi Richard, interesting observations re cam timing, I'll take it into account with the 270 type cams. I tend to only advance with high lift rockers as a matter of course.
Peter
Peter Burgess Tuning

Interesting , Richard's view on the cam timing--
I've always set cams up three or four degrees in front because that was how I was taught 200 years ago - The reason given was to allow for mechanical stress under load and the thought was if they were set to spec they would be behind a bit when running -
I'm a bit of a camshaft Nerd and have tried everything going- Having an agreeable mate that grinds cams helps with my addiction but it can be a bit of an expensive habit though.
Cheers
willy
William Revit

Allan, why "not the rule of 9"? Assume "valves are rocking" is when each cylinder is at tdc power stroke - wouldn't result be the same?
Mike
Mike Ellsmore

Mike,
I found the R of 9 on one of my engines left the tappets a bit rattly, and with slight movements of the camshaft there was a "lower" spot on the back of the cam.(depends on the grind I suppose) Initially i just found that low spot to set them, but 'rocking' on the compression stroke meant I could find that spot and do both valves at once. Seems to work!
Allan Reeling

"wouldn't result be the same?"

Depends. In theory at least half the base circle on the opposite side of the lobe should give the same clearance, but in practice it can vary noticeably. I could never get repeatable rocker clearances on my roadster at the 'rule of none' point, until I decided to find just where the biggest gap actually was. Several valves had it before and several after, and I know of several other cars that are the same. Since I started adjusting at the point of biggest gap they are repeatable, and the valve train is quieter.
paulh4

Yes, in theory the base circle should be concentric with the camshaft, in practice tired grinding machines and poor operators can result in quite a bit of run-out.
Paul Walbran

HI Peter,

Now mobile again and have checked the crank position halfway between No1 Exhaust and Inlet just rocking. seems to be exactly TDC. Valve clearances are at 014 Inlet and 016 Exhaust. Will ring to see if you can fit me in.

Regards
Graham
G Cherry

My Crane 270 works well and has the smooth idle @ 1000. Yes there is a slight "lope" in the idle, but it's just the engine "singing it's tune" smoothly

:>{D

Cheers
Gary
79 MGB
gary hansen

Grahame, Are those Piper's recommendations for valve clearances? I seem to remember my 270 had bigger gaps.
Allan Reeling

Hi Allan,

Yes as AFAIK, they were given to me with the data from the engine builder, maybe Peter will change them when I see him next week.

Graham
G Cherry

It depends which version of the 270 is fitted.
Peter
Peter Burgess Tuning

The information I had mentioned a BBP270 and gave the cam timing and valve clearances as follows:-

The cam timing said 107 deg BTDC but I think that was a typo and should have read ATDC.
Valve clearances were 014 inlet and 016 exhaust

I guess the engine builder will have thrown out any further information by now, since it was built in Sept 2013.

Graham
G Cherry

Hi Peter,

What a transformation, the car is now lovely to drive, nice and smooth at low revs and all the way up through the gears, all the lumpiness has gone. It was a pleasure to drive it home even in all the traffic.

Thank you so much
Graham
G Cherry

It was worth it all to see the grin on your face after you road tested it Graham, a lovely car and glad it is running sweetly.

Peter
Peter Burgess Tuning

This thread was discussed between 06/10/2016 and 02/11/2016

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