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MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Cam timing.

I'm thinking about re-timing my cam.(731cam,1133cc,HIF44,LCB,straight through custom silencer)
It is currently set at 107' courtesy of an offset key. This is 3' advanced from the factory quoted figure of 110' for a 731.
I'm not looking for the pros and cons of the 731. It's what I've got and what I'm sticking with, as I can't financially justify changing it.
What I'd like opinions on, is could any improvements be gained by further altering the cam timing, and if so, what to?
Thanks as always.
Bernie.
Bernie Higginson

I would follow the suggestions of the maker of the camshaft because only they know exactly how and why the cam is ground as it is. I have recently installed a Kent camshaft in my 1500 and downloaded the timing spec from their website.
Nick Nakorn

Bernie, have you checked out Vizard? I suspect you may have done which is why you have used the offset key to give an additional 3' of advance.
The other thing I learnt was just how far out the cam sprocket marks were when I "dialed" mine in.
Guy W

Guy,

I saw this when helping a neighbour with rebuilding his Ford X-flow engine, he had to buy an adjustable cam sprocket kit to get the timing right as the offset pins in the X-flow case wouldn't quite get it right. What you have to take into account is that the cam grinder, if doing a regrind, has to fit the altered profile and timings into the original cam blank and may alter the timing to do so relative to the original marks, you don't want to reduce the cam sizes too much or you risk increasing the surface loadings too much and as many hot cams have higher accelerations they have a balance to make to achieve good cam life which various makes at some time seem to have had a reputation for not achieving. I would hope that if you bought a cam to OE spec or a new billet cam then the marks would be correct but have never done so.
David Billington

Yes David, I realised why, and maybe if I had been using an original standard cam it would have been much closer.

In practice mine was so far out I used the next tooth round on the cam sprocket and an offset key, which I had expected to need to advance it went in to retard the setting and bring it spot on to +4', which is what Vizard was recommending! Really fortunate!
Guy W

Vizard does not like the 731.
Don't understand why though it works fine in my 1380.
Not sure if anything can be won in the timing.
Might be interesting to look at rocker ratios
Onno K

I used a 4' offset key, so I suppose I could be 1' out in my calculations on the dial gauge and it is actually 106'.

Yes Onno, Vizard gives the 731 a bit of a slagging in his book, but as you say, it works OK in your 1380. Maybe I'm expecting a bit too much from 1133cc. Is yours timed dot to dot?

In its current set up, it pulled a tad short of 50bhp at the wheels on Peter Burgess's rolling road, which Peter said equates to about just under 65bhp at the flywheel.

Guy. I read on another forum that one tooth gives 18' of difference to the cam. I did consult Vizard and bought a set of three offset keys from Moss, 4' 7' and 12'. And plumped for the 4' one.

I'll have another play tomorrow and see what measurements I get. Only trouble is, I won't know what it's like until I drive it.

The reason I asked the question in the first place, was I wondered if anyone had any experience of different timings with this particular cam.
Bernie Higginson

Sorry. Edit.
David. I bought the cam new, years ago, and I believe it to be an original Abingdon billet cam. Maybe it's a bit worn. I've not had it out for a long time, but valve clearances are OK and it's not noisy.
Bernie Higginson

Bernie
Around 3deg advance is usual practice, any further like 7 or 8 starts to take a bit of top end out of it
You could go back to standard specs (0)) but probably wouldn't gain a single thing but could possibly loose a bit of bottom end and make it a bit more peaky than it is at present -- It just depends on what you are trying to achieve
willy
If you are simply after more of what you have where you have it maybee Onno's sugestion of some rockers---
William Revit

Hi Bernie

The three degrees advance is probably a good idea to get some bottom end pick up into a lazy cam.
The 731 is the same grind as the 714 MGB cam, it revs into oblivion but does nothing except lose bottom end power, I never understood its raison d'etre as a cam until Ray Downes (MGOC race tech man) who worked on the first Minis for rallying ( he said great car for rallying but will never sell as a road car!) the 731 was a rally cam for shale use ie the engine needs to rev but no sudden input of torque to spin the tyres! Sums up the characteristics to a T, cam does the designated job just folk fit it for road use.

Mind you....maybe a good 'snow' cam for road use?


Peter
Peter Burgess Tuning

I was under the impression that if you are using 1.5 ratio rocker gear advancing the cam could give you even more gains.
R Mcknight

Peter
I tried a 714(rally) in a big capacity B once and it was horrible
It did absoluteley nothing very well and ran out of what little it had at around 5000
It relates to what you say a bit In something smaller it would probably sit there and spin all day but it certainly isn't a big breather
It would be interesting to see what one worked like with a good set of rockers though
When you look at his 50hp at the wheels I guess it's not really coming up with the goods as is

willy
William Revit

Hi Willy

The 714 used to be the 'weapon' of choice in the standard race B engines, legal lift but illegal duration, I think the standard cam at 108 degrees was more effective. Kent sold a'Standard Race Blue Print Cheater Cam' for MGBs it transpired it was the Ford BCF2 grind. That worked a lot better than the 714. Piper superseded the BCF2 style cams with the 929 when MGOC and MGCC allowd any duration cams but std lift either at valve or cam for the regulations.

Advancing the cam has always worked with high lift rockers but one of my customers just bought a swiftune cam and high lift rockers and was told to time the cam at the advertised 106-108 figure even with high lift rockers.

Peter
Peter Burgess Tuning

I have bog standard pressed steel rockers, so maybe that's what I should be looking at. I'm also running with standard clearances.

Recently on a trip to Holland to the Healey museum, we got to have a blast round Zandvoort track. My friend Les Robinson who has a mk2 Sprite 948cc with a Swiftune SW5 cam and he could pull away from me out of corners. It was only as the revs rose that I could catch up with him, even though I had the bigger engine. He did however have a P. Burgess head. My head is standard except for having been skimmed. I get 200psi on all cylinders. Maybe getting the head flowed and changing rockers would help, or will I have to bite the bullet and get rid of the 731?
Bernie Higginson

Hi Bernie, the 731 is a poor cam but maybe wait till it dies? The high lift rockers would make it worse.

Peter
Peter Burgess Tuning

Mine is timed dot to dot.
The capacity might make up for the lazyness as it has no problems pulling a 3,9 diff from 2500rpm.

Though I should finish a different engine soon (just need to fix my spare gearbox then) ditching the 731 for a 286
Onno K

Thanks everyone. I've kept the 4' offset and put it back together with a new uprated chain. The one that I took out had stretched quite a lot after only about 3000 miles. It came in the Duplex kit, so was probably a budget one. The new one cost three times as much as the regular ones that Moss sell, so should be OK.

Peter. Thanks for the advice about high lift rockers. Saved me some money.
At the end of the summer when I've saved up my pennies, I'll come and see you to see about flowing my head and a suitable cam.
Thanks again.
Bernie.
Bernie Higginson

Peter, we had to maintain standard lift with a tolerance (12 thou I think) when we ran my B in 1985 Rally of NZ (WRC round that year as I recall). Ended up with a Ford A6 profile, 320 deg duration and .010 more lift than standard B so within allowed limit. Worked very well, finished in the top half of the field (just)!

And agree with above comments on 731 re advance ... though in the B series we've generally had better results with a bit more advance (7 deg) than in the A series (4 deg).

Most of the standard BMC cams were at 110 deg, so the 731 wasn't that much different in that respect.
Paul Walbran

I'm progressing slowly through an engine re-build on my (formerly) 1275.

With a +.040 rebore I was advised to fit a vernier cam drive, which I now have, to ensure accurate cam timing.

The cam is standard, but I would like to get the best performance out if it which, for hill-climbing, means considering improving the bottom end acceleration.

Vizard recommends a maximum advance of 4 degrees, and Peter Burgess suggests that 3 degrees is about right.

As I'm not planning on heaving the engine in and out on a whim to fiddle with settings so I really only want to do this once.

Do I set it at 3 degrees on the assumption that there will, in time, be a bit of chain stretch taking it closer to 4 degrees, or should I just be content with Standard and leave it at what I hope will be a more reliable 0 degrees than with the original sprockets?

Apart from the existing LCB exhaust and K&N filters, there have been no other performance mods to the fuel or ignition systems and just new ARP bolts in the rebuild for peace of mind.

I'd love to know your thoughts.

A very indecisive Colin
C Mee

Hi Colin.
Are you timing it with a dial gauge? I know when I did mine the dimple marks on the sprockets were a long way out, so would not have made a good starting assumption. I timed mine at 4 degrees, using a stepped woodruff key. I didn't see the benefit of a vernier set if I could get the key to do it as my hope was to do it once and never again! The stepped key got it spot on with a bit of juggling around with the chain, sprockets and key.
GuyW

Hi Guy.

I have a dial gauge. Just waiting for a magnetic stand to arrive.

I'd only seen 1 degree offset keys until after I'd bought the vernier! Although I don't plan on repeat engine extractions, I might, at some stage, go for a better cam so I'm happy with the route I've taken - so far!

Has your engine had other performance upgrades along with the timing advance?
C Mee

Yes Colin, I have a few other upgrades.
Skimmed MG Metro big valve head, 276 cam, HIF 44 carb, Maniflo header, balanced everything.

I bought 3 or 4 Woodruff keys of various offsets. They were just a few pence! The standard dimple marks were way out. It's a good while ago but I got the advance I wanted by moving the chain on by one tooth, and then using a stepped key to bring the advance down from the excessive advance that had created.
GuyW

Thanks Guy - all things I'd like to add in the future when funds allow!

I managed to do it again with this job - go down the expensive route when there's one that only costs pennies:)

Still, I think the vernier wheel looks pretty cool - shame it won't be on view when the engine's finished - I'll make sure I take some photos to remind myself!

Thanks for your input - much appreciated.

Colin
C Mee

<<shame it won't be on view when the engine's finished>>

If my name was Prop I would excitedly encourage you cut a hole in the front of the timing chain cover and glue a piece of perspex in with JB Weld to display it!
GuyW


>>>Do I set it at 3 degrees on the assumption that there will, in time, be a bit of chain stretch taking it closer to 4 degrees, <<<

Wouldn't chain stretch reduce the advance, rather than increase it? Or am I misunderstanding something?
Greybeard

You are correct, Grey.
Dave O'Neill 2

Guy - Now that would be cool!

Grey, Dave. Thanks for putting me straight on that. I'm sure that was what I'd read somewhere but that's exactly why I turn to you guys to put me straight. Much appreciated.
C Mee

>>cut a hole in the front of the timing chain cover and glue a piece of perspex in<<

ISTR a certain former BBSer doing just this to visually observe how oil drains from the timing case.
Remember the Great Oil Sucker Thread?
I thought it was a good idea in that context.
Greybeard

Grey, I remember it well!

Still mulling it over, especially as the rebuild was prompted by oil sucking/blowing.
C Mee

Grey, you are quite right about the oil viewing window suggestion. I think the context of that suggestion was somewhat driven by frustration on the part of He Who Shall Not Be Named, over those who doubted the specific oil sucking syndrome he was investigating.

As a viewing window for showing off Colins Cool Cam Vernier, it seemed more appropriate to attribute it to our good friend Prop.
GuyW

lol----------

https://www.med-engineering.co.uk/vernier-belt-drive
William Revit

I want one! :)

But sadly I don't need one - and I've already spent more than enough as it is.

I think I'll just stick with what I've got but with a PROPer LS-style Cool Cam Vernier Viewer.

C
C Mee

>>As a viewing window for showing off Colins Cool Cam Vernier, it seemed more appropriate to attribute it to our good friend Prop.<<

Quite right, but why stop there when there's tappet covers and a rockerbox lol! He was halfway there when he left the bonnet at home haha!

Can you still get those HT leads that flash when they fire?

Willy that kit looks so cool.
Greybeard

I've got a timing belt drive on my A series and I've been told it produces a sound much like a turbo whine, I can't hear it myself in the car over the rest of the engine noise but bystanders have mentioned it.
David Billington

Finally got it installed and all closed up, so here's a last look.

I still think it looks pretty cool!

Everything else on the car looks mass produced, this looks a bit more bespoke (even though I know it isn't).

Still mulling over the transparent timing cover - perhaps vacuum formed perspex? One to think about the next time the engine's out.

Colin


C Mee

Lovely! If it works as well as it looks you're all over it.
Still loving the seethru timing cover idea. In fact I think I'm going to nick it when I get around to rebuilding the spare 1500 engine.
Greybeard

Greybeard, since most modern cars use an externally fitted cam belt, that might be an alternative way to go. Then hiding it behind a (safety) cover would be entirely optional.
GuyW

Hmm..
Not sure that's easily achievable even on a 1500 Guy as there is a lot of oil swilling around in there. Also, colour me old-fashioned but I'm not a big fan of belt drive cams. For me a chain is a much better idea, especially when it's like Colin's beautiful duplex setup.
By a strange happenstance I have an old timing cover under the bench. It's off a 6 cylinder engine but it's the same as the 4 and it's a bit rough and dinged up so I might have a bit of a play with it. If I can find it of course!
Greybeard

Quite right Sea Gorilla! I was only suggesting. I imagine in theory it might be possible to engineer a crank seal and presumably one on the cam shaft too, and then have a rubber belt drive that operates 'dry'.

But a Lexan window set into an old chain case cover might be fun to experiment with. But you may just find that your view of the bits inside whizzing round is completely obscured by a surge of oil!
GuyW

It shouldn't be too difficult. Belt drive conversions are/were popular on A-series engines.
Dave O'Neill 2

This link i put up earlier was a belt drive--

https://www.med-engineering.co.uk/vernier-belt-drive

Definately need a cover on a belt drive, there have been plenty of good engines killed running dry sump pumps that have had a little stone get in the belt and, poof, gone

On our old racer chev we ran a belt drive fuel pump for a while and had issues with gilmer drives breaking belts, which reminds me,,we went to a camshaft driven pump mounted on the timing cover
The cover had a bolt in plate for adjusting cam timing and it got modified to take the pump driving off the end of the cam and it could still be removed to get access to the cam sprocket bolts to adjust the timing as well--Can't remember the brand but probably Milodon-----like this one-but in aluminium
William Revit

Ha ha you thought i forgot the pic.
You could mod a cover to be like this, even with a perspex window instead of the plate, that'd be special----------Oh NO not an oil sucker cover

lol


William Revit

Interesting stuff.
I've only ever had two timing belts snap on me - both on (frankly rather neglected) Pinto engines that both survived the experience. I fairly dread it happening on the dreaded Volvosaurus. It got a new one last year when the alternator/steering pump belt called it a day. Just replaced them all at the same time for a bit of peace of mind.
For some reason a few years ago there was a spate of snapped final drive belts on Harley Davidson bikes. I changed five I think in a fairly short spell. I've vaguely wondered if there was a batch of bad belts or if people just stopped taking the guards off. IDK...
I had a quick look at the cover in the Shed. It would be dead easy I think and it might be interesting to see just how much oil is washing around in there. On the other hand given the 1500s scary oil pressure foibles perhaps I'm better not knowing lol!
I once casually remarked to the Leader of the Opposition that I wished the dishwasher had a glass door like the washing machine as I was quite interested to know what was going on in there. I've been mocked unmercifully for it ever since!
Greybeard

Grey, if you "wanted to know what was going on in there" you could have read the label. I think there is a clue in the name. Dishwasher? - bit if a giveaway, - no?
GuyW

And there it is. Again with the mocking...
Hahaha!
Greybeard

The cam belt on my Peugeot 405 went when I lifted off for the roundabout outside the Gaydon Land Rover plant after cruising at a steady speed on the old A41. The RAC guy who picked me up said it's not unusual for belts to go due to backlash in a sudden transition from drive to over-run. I'm not sure exactly what failed as one look under the cam cover was enough to say it was scrap but I suspect the idler wasn't changed along with the belt and it took the opportunity to seize. After that I generally de-clutched before easing off the throttle, giving a much gentler approach to junctions and similar situations. Now I just ease off gently and enjoy watching the consumption readout drop to 0 as it goes onto over-run.

Talking of Volvos and cam failures, in the early '70s, our neighbours set off to tour Scotland with his brother and wife in the brother's brand new Volvo. Somewhere around Edinburgh it lost all power and was clearly sick so they took it to the main dealer. The camshaft was completely shot, but, even though it was a brand new model, they were back on the road the next day. Volvo had discovered that a batch of camshafts hadn't had the proper heat treatment or some such, but they didn't know where the affected camshafts had gone to. They knew the duff engines would be turning up pretty soon so they had sent out batches of replacement shafts to all their dealers to be ahead of the game.
C Mee

This thread was discussed between 29/01/2015 and 04/05/2020

MG Midget and Sprite Technical index

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