Duplex chain end float

[tysonn]

Undoubtedly.

[philthehill]

bmc
Whilst you may be able to do the timing with a set of feeler gauges and a chopstick I prefer to use a dial gauge to determine TDC and another dial gauge to determine max lift of the cam and a timing disc to determine what degrees those positions are in relation to the crankshaft.
Then with it all worked out I set and lock off my vernier adjustable cam gear and then after turning the engine over several time set about checking it all again to confirm the setting.
That is where the infinite patience comes in.
With a high lift and long period cam, a decked block, a skimmed head and 1.5 to 1 ratio rockers I cannot afford to get it wrong.
And to make doubly sure that when fitting a new cam for the first time that I have adequate clearance between valve and piston I put a strip of plasticine on the top of the piston assemble the top of the engine (with an old head gasket) turn the engine over, then take the head off and check the thickness of the plasticine. You cannot be too careful about working clearances.
The above processes have served me well over many years of BMC 'A' series engine building and modification.

[alexmcguffie]

Philthehill, a good description of how to do a propper job

[philthehill]

Alex
There is great satisfaction in doing a job properly
Phil

[bmcecosse]

For a competition engine - undoubtedly the way to do it..and I have done so in the past. Although I still argue that unless you check the power result on a dyno - you are setting 'blind' . To check the cam timing on an ordinary A series - the feelers do the job very well indeed.

[tysonn]

I'm just off to read Janet and John go up the hill.

[les]

There must have been many engineering shortcuts over the years, wonder how many have paid off though?

[philthehill]

Mick
Unless you are into engine tuning I would suggest that Janet and John is the better bet
Phil

[mowogg]

I have just been having another look tonight. i have reversed the thrust plate (which was slightly worn) and reassembled for comparison (note you can only get two bolts in as its drilled offset to ensure it is fitted the correct way around)

anyway this has removed about 50 % of the movement, but i still think its the collar on the timing gear which is not correct. the movement is not as large as i first though but it is still way too much .

[bmcecosse]

Have you tried without the key? And the securing nut is tightened right up ? If you are SURE the problem lies with the sprocket boss - you can carefully file it down till it's right - but check first how that will affect the chain alignment with the crank sprocket.

[philthehill]

I have just checked the max depth of the centre boss of the camshaft gear on a after market duplex set and a high quality Kent Cams duplex set and they are both 19.4mm. Both sets of cam gears have been used but have completed very few engine hours; they have given no problems at all and fit correctly as expected.
The raised ring that fits against the cam shaft bearing face on the after market gear is 2.8mm high and on the Kent Cams gear 3.0mm high.
Both raised rings are 21.5mm O.D.
Placing a straight edge across the raised ring and measuring the gap between the straight edge and rim of the gear is 6.5mm on both cam gears.
If the cam gear fitted to your engine gives the same measurements then there is nothing wrong with your cam gear and you will need to look else where for what you consider excessive for and aft (lateral) play.
Attached is a picture of the Kent Cams camshaft gear (camshaft face) for comparison.[frame][/frame]

[alexmcguffie]

Mowogg,
I'm assuming you have the oil pump fitted while you are fchecking the cam gear?

[bmcecosse]

The oil pump makes no difference - the cam doesn't bear against it. The cam is locked between the triangular plate and the extended spigot hub of the drive sprocket.

[philthehill]

bmc is correct.
If you look at the sectional drawing taken from the BMC wksp manual you can see that the oil pump is not bearing on the end of the camshaft. This will be the same for the slot or star drive.
The front of the cam shaft is held by the location plate which is sandwiched between the camshaft front bearing face and the camshaft driving gear/sprocket.
When the engine is rotating the thrust on the camshaft is forward (towards the locating plate) and mainly caused by the turning resistance exerted by the distributer drive spindle/shaft (Pt No: 12G4499). The cam followers in theory should not exert any lateral forces on the camshaft. Because of this forward thrust on the camshaft the thrust side of the locating plate is or should be a white metal bearing surface similar to that of the con rod/big end bearings. That is why it is important to have the bearing surface towards the cam thrust face. The camshaft face of the camshaft driving gear/sprocket is not a thrust face and that is why it is left as a semi-machined face and does not and should not come into contact with the camshaft locating plate but must butt up against the camshaft thrust face.[frame][/frame]

[MarkyB]

the camshaft the thrust side of the locating plate is or should be a white metal bearing surface

Oh dear, I wasn't aware of this and I'm pretty sure I turned the plate to present an unworn surface to the cam
I've never seen any evidence of white metal on this plate but never looked carfully either.
As the car isn't running points I'm hoping the thrust on the cam will be much reduced.

[les]

It isn't that obvious, so I bet many people have assembled it wrong. You ought to rectify it though.

[MarkyB]

I've had a look in the workshop manual and it makes no mention of the plate having a bearing surface, I'd expect the plate to have an F stamped on it to suggest the correct fitment.
I don't remember seeing one but my memory isn't that reliable these days

[les]

Well it does have white metal side. I say that because mine has! Makes sense as the cam face is in contact with it.

[mowogg]

I don't think its possible to get the plate on the wrong way around. The screws are offset which only allow for it to go the right way up in one position.

Phil -thanks for the measurements. Mine is somewhat different. The boss centre is 18.55mm (compared to 19.4mm) and the ring face is 2.5mm vs 2.8 mm.

I think this brings me back to where i started, in that the part is not machined correctly.....

Any recommendations via PM of one which fit with the correct tolerance?

[bmcecosse]

The plate can indeed only go on the right way round. If you are SURE the endfloat is 3mm or so (check WITHOUT the key fitted.) .. - then you must carefully file the spigot boss on the sprocket till it fits in snugly with the right amount of float Just take your time -it's not difficult! But then you must check the alignment of the chain with the lower crank sprocket. As an aside - have you countersunk the two holes and fitted countersunk screws on the front plate ?