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MG Midget and Sprite Technical - Camshaft timing, CONFUSED

Allright not much has happened in the last month but today I fitter the new adjustable camdrive to the 1275, I used a dial indicator clock to get the no 1 piston TDC (the head is off) then a pushrod and set the camshaft so that is has full lift TDC, or maybe I should say the maximum lift that the adjustable camgear allows me to set after lining up the dots. I used Vizards book as reference but I'm still confused. I don't know if I even got I right to begin with this far. I've got a kent 276 cam and they claim that no advance is required, but the book does not. So how do I go about setting the degrees? Do I fit the protractor on the crank loosen the bolts on the camdrive and retard the crank? Should I set the cam retard or advanced or just leave as is?

Please bear with me on this one, first engine rebuild and all.

Cheers
Alex
Alexander Sorby Wigstrom

I'm sure someone will be along with a much more complete sequence but basically.

Put protractor on Crank. Find TDC of No.1 Piston (with DTI)- set a pointer to read 0 degrees on the protractor.

Put a pushrod in and move the DTI to read the lift on the pushrod.

The CAM manufacturer should specify the timing required (kent 276 should be on the web somewhere). Rotate the crank in the in correct direction and adjust the cam gear until you get full lift at the specified timing setting (something like 110 degrees after TDC).

The setup should look something like this....

Mine was a fixed cam gear - and having done the dry build I ordered the right offset key to get the timing spot on. I could never see myself endlessly tweaking cam timing so didn't go for a full vernier cam drive.

Dean Smith ('73 RWA)

Importantly you use no#1 inlet pushrod...i.e. the 2nd hole.

A more detailed guide than I could ever hope to write! .....

http://dl.dropbox.com/u/19278540/pdf%20files/HowToTimeYourCamComplete.pdf

Dean Smith ('73 RWA)

Turn the engine in the direction of rotation only when you are measuring max cam lift as the slack in even a new chain will give a false reading if you turn the engine in both directions...

Cam max lift with a dial gauge can be found by identifying (say) 10 thou before max lift on the dial and 10 thou after, taking a reading on both, adding then dividing by 2, this is because cams tend to have a flattish nose profile and it is sometimes difficult to see exactly when you are on full lift...

JB
James Bilsland

Hi,
There are sonme good articles 'and step by step guides on the mini spares site.I will show the link,but if I mess that up it is in the articles section,Calvers Corner under Camshafts.
http://www.minispares.com/Articles.aspx?ty=alaid=0214title=Calvers%20Corner~Camshafts
On discovering I had a Kent camshaft I emailed them and they came straight back with the setting required for my camshaft

Regards

Mark
M Teal

Alex

If I understand your post correctly, are you trying to set max cam lift at TDC? Max inlet cam lift for the 276 is at 106 deg after TDC. You should:

Find TDC as you have done.
Fit the protactor to the crankshaft so that it reads zero.
Turn engine forwards till protractor reads 106 degrees.
Then adjust vernier to get full cam lift at this point.

Finally, check that you have it correct by turning the crank with a dial gauge on the pushrod and seeing if full lift is at 106 degrees as it should be. The method James outlines above is very good for that.
Paul Walbran

Thanks guys I think I now have it sorted, it'll be great to finally assemble the rest and slap some paint on it!

Alexander Sorby Wigstrom

I think Alexander is now happy so hopefully won't mind a slight (related) diversion of this thread.

I rebuilt my 1310 engine last year, upping the capacity to 1380 and getting the combustion chamber volumes balanced for a 10:1 CR. No other changes. I continued to use the 649+ cam and 15:1 roller rockers. In previous thread I had been advised by none other than Peter Burgess to set the cam timing 4 deg earlier i.e. 96 (becuae of the roller rockers), than the 100 specified by Pipers.

I did all this and on the rolling road (the same one used for earlier runs), I was getting a small (2-3BHP) increase in power and torque but at much lower revs - 5950 instead of 7100 previously.

Now that's a big drop in revs so I am wondering if retarding the cam 4 deg has caused this?

Any thoughts?

Regards

John
John Turner (Midget & MGB)

That's what the theory suggests from advancing the cam - peak power occurs earlier and torque improved.
Paul Walbran

I would have thought peak power should be about 5900 for that setup, 7100 seems way too high, also remember you now have a larger engine and peak torque and bhp gas velcoities will occur earlier, or did you mean the power figures are for 1380 b4 and after cam timing difference? Did you do anything with the tappet clearances to suit higher ratio rockers?

Can you post the two power curves so we can see?

Also CR might be better at 11/11.5 to 1 (13 to 1 for competition).


Peter
Peter Burgess Tuning

Peter

Thanks for responding. Power runs were for the 1310 with the 649 set to 100 deg and then the 1380 with the same cam set to 96 deg. The 7100 (actually 7021 I see now, for the 1310) is in the range quoted by Piper for the 649+

Regarding tappet clearances, this is another area where I have received apparently conflicting info. My dyno man (used to A series say they 'like em loose' approx. 19 thou but I have seen tighter clearnces mentioned elsewhere - what would you suggest?

Will scan and upload before and after runs ASAP

John
John Turner (Midget & MGB)

Hi John
Peak at 7000 is very high imo, it may depend on the dyno sampling.

All things being equal it may be the case the peak bhp port gas velocity is directly related to difference in engine size ie (1380/1310) x 5900 = 6200 for peak bhp with 1310 cc which may be more realistic.

Tappets settings go for quoted setting x (new ratio/old ratio) 17% more gap if 1.28 to 1.5 ratio.

Did the CR remain the same for both engines?

Peter
Peter Burgess Tuning

Peter,

This is the 1380 dyno curve.

The cr was increased with the 1380 upgrade - I asked for 11:1. Don't know what it was withthe 1310

Thanks for the guidance on tappet clearance - will try 1.17 x stock clearance

John

PS Low top end speed is due to a 4.5 diff





John Turner (Midget & MGB)

Did you have the same diff with the 1310? What gear did they do the pull?

Peter
Peter Burgess Tuning

Peter

Same 4.5 diff with the 1310

Curve uploaded

I think the rpm is correct as my tacho was calibrated and it was running up to 7000 easily with the 1310 engine

John

John Turner (Midget & MGB)

Hi John

I still feel the peak at 7 is high, if you are ever up our way I would love to give it a run to see how it goes on our rollers. We are in the midst of refreshing a 1380 full race engine, it will be interesting to see what that peaks at.

Peter
Peter Burgess Tuning

Just noticed an oddity. You are pulling 13.25 per thousand with 1310 but 14.83 per thousand with 1380. Any reason why?

Peter
Peter Burgess Tuning

Umh? Checked back to the car spec of the dyno run with the 1310 and I was running the 4.5 diff then, as with the 1380.

Now makes me wonder if the 7000 rpm was correct although my tacho seems to corroborate that.

Although the dyno was the same for both runs it had been physically relocated although I was assured that it had been correctly 'calibrated'

John
John Turner (Midget & MGB)

could different tyres or pressures account for the difference?
David Smith

problem could be running one in 3rd gear and t'other in 4th gear? 3rd gear runs tend to show higher power than 4th gear runs but lower power losses.

You cannot compare 3rd and 4th gear runs. However I am still suspicious of your first curve peaking at 7000.

Peter
Peter Burgess Tuning

Tyres would have been the same but can't say if pressure were.

Also I don't know what gear the runs were done in - I wasn't present.

With the 1380, whilst I was initially dissapointed with the power increase (and the lower revs as I was well impressed with 7000rpm!), the improvement in torque was significant and for a sprint/hill climb car very useful

The car is in the garage awaiting repairs to some 'unintentional body modifications' but once back on the road I will try to see PB and have a run on his dyno

Thanks again to all for your input

John


John Turner (Midget & MGB)

Hi John

You are most welcome to watch and join in while we dyno your car, we prefer it if customers are with us, after all it is your car.

Peter
Peter Burgess Tuning

This thread was discussed between 06/01/2012 and 12/01/2012

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