Camshaft timing

I think I recently read that the cam fitted to US market 18V engines is retarded by 4 degrees or so from standard, is that right? If so is the cam itself different (lift, duration etc) or is it the same one as Euro spec cars but with a different timing set up? If it is the same cam is it relatively simple to retime it or even worth the effort?

Reason I'm asking is I understand that the stock cam is pretty good for general road use but it makes sense to me that it would be even better if installed as originally intended. I am intending to boost the compression a bit, not sure yet if I will go with high comp pistons or just a head skim but want to get a full picture of where I am against a stock Euro spec engine first. Car is a 72 year of manufacture.

What do we know folks?

I can't remember (am at work and don't have Peter Burgess (Power Tuning a MG) book here) but the cam timing was changed in the later cars and when I rebuilt my engine I did set it up to the previous timing and notice an increase in the power output. Get Peter's book- it has an excellent discussion on camshafts and timing. I

There has been fairly extensive research on the subject. Kelvin Dodd had some particularly good comments.

It appears that a couple of things happened that led to the camshaft being advanced 4 degrees in 18V engines compared to 18GG series engines. Kelvin pointed out that BL was trying to make more things common across a number of automobiles. He believes that this may have been one of the drivers for the change. It seems to me that Kelvin mentioned a particular Austin that preferred the advanced timing (and was probably being sold in larger numbers than the MGB).

A second factor was the switch to a single carburettor. Because of the strangulated single carb setup, the car no longer breathed well at higher RPM. Advancing the cam timing moved the power band downward. An 18V engine might even have more HP than an early engine down at 2500 RPM.

The change appears to have been made via a switch from dual row timing sprockets to single row timing sprockets. You can easily change an 18V to 18GG timing by going back to the dual row sprocket. BUT - unless you change the carbs (and possibly the ignition curve), that might make performance worse. It definitely won't make it any better.

I hope I have not misquoted Kelvin - you should look up the original extensive discussion on the subject.

I am new to all this (and have actaully never done this), but if the single row timing chain is still in good shape, could you just put in a 4 degree offset key?

So are we saying it is the same cam? If so has anyone done what Evergreen suggests? My car was delivered with dual SU's so I dont see breathing as an issue. Terry, I shall search for Kelvin Dodd's stuff as advised.

You could, but a replacement double row is inexpensive and twice as strong. A degree wheel and dial indicator will be in order. Also, I agree buy Peter Burgess' book. Or better yet, give him a call and buy a piper cam!

I agree, the double row chain swap is fairly inexpensive. Just was wondering if anyone has tried the offset key. I am new to owning this car and see that the double row chain is stronger, has there been problems with the single row chain?

Kelvin also pointed out that the switch to single row sprockets occurred before the change to single carbs - so that was definitely not the only reason the factory switched. I suspect Kelvin is right that it was an effort to reduce the parts count. Also, never overlook the effect of emission regulations during that epoch. Maybe they found that the emissions dropped a bit at the test speed with a 4 degree advance. But it certainly was a good idea for the single carb cars.

If you have dual carbs, then I would definitely switch sprockets. The offset keys are so expensive that they aren't all that much cheaper.

As to whether they changed the camshaft, that has been a difficult question to answer for certain. I don't think so, or if they did, the change was minor. However, I am told that the part number changed several times. But BL did that sort of thing even when the part didn't change so that is not a guarantee.

I just checked the Parts Fiche (which is getting harder because the stupid DVD doesn't work on Windows 7 - and I'm down to only one machine with XP) and the 18GB, GD, GG, GH, GJ, GK seem to have used the 88G 303. The 18V engines used the CAM1156 beginning at change point 18V/797AE/101ON, 18V/801AE/101ON and 18V/802AE/101ON . Was this a real change or just a change to a new numbering system?

And, the change point for the camshaft/crankshaft gears is not the same as the change point for the camshaft.

As usual, I'm not sure what to conclude from this.

My personal belief is that if the camshaft changed at all, it didn't change much.

According to Pete Burgess the cam timing changed with the 18V engine to 20/52 55/17 compared to the earlier cam timing of 16/56 51/21. I used an offset key and also a cam degree wheel to set the cam timing back to the earlier 16/56 51/21 position. It was not just a straight 4 degree swap as the correct timing will usually not line up the the "line up the dot" method of cam timing.

The last late B I owned I rebuilt with HC flat top pistons, Mild Piper cam, dual HIF's with custom cold air box. The current owner claims to have no problem staying with 215 V8's:smoking:
My current 80'B has not had the time and attention the last one had yet.... But I have converted to dual HIF's and dual row timming chain and of course a offset drift key to time it correctly. If you just time it by "lining up the dots" you will still be off so many degrees:eyepop: The car runs great for "stock" with just those mods. It only had 34,000 miles on it when I purchased it a couple of years ago. Since then besides those basic engine mods I have lowered it to CB height, aftermaket wheels and Boss Frog roll bars (I rolled that last one with no roll bar then rebuilt it again and the wife said if I drive it I WILL PUT A ROLL BAR IN IT!). Anyway, back to timming... Make sure you have a degree wheel and the opening and closing degrees of the valves so you can check with your dial indicator(you have one of those too don't you?)I just happend to have one offset keys left from when Moss sold them in a set of 3(?) and it was one of the larger offsets, can't remember the # right now or which direction. It took me better part of a day to quadruple check which direction/position to put the key in:X I know some guys say "Its so easy with adjustable timmming wheels" but hey, my labour is cheap;). Since the engine only has 42,000 miles on it now I don't want to rebuild for a while. If anything I might skim the head for higher compression. I would read "Power Tune the MGB" and use that as your Bible. In it I believe Peter stated a winning MGB that had a stock profile cam, albeit with other mods...
Dave

I believe the cams were pretty much the same. The 4 degree retardation in the timing was, indeed, for a reduction in emissions. The 4 degrees does improve the low end power, but at the expense of power in the higher rev band. RAY