TR6 Cam Timing

[colin3511]

Hi,

 

I have an original 1972 TR6 engine that I have just rebuilt. I want to use the original timing marks to line it all up. Looking at the internet the cam and cam gear dots are shown next to each other. Mine are there but the gear and cam dots are pretty much on the same PCD. Do I put the cam dot on the left or right of the bolt hole?

 

I hope that makes sense!

 

Any thoughts would be appreciated.

 

Thanks,

 

Colin

[john.r.davies]

From memory, the dots on crank cog a cam sprocket should be 'together' on the perimeters facing each other.

 

The two pairs of bolt holes aren't interchangeable. Triumph went to the trouble of offsetting the two pairs of bolt holes to allow the timing to be set more closely than one tooth,by using the other pair for half a tooth, or by turning the sprocket over, a quarter tooth either way. See the WSM!

 

John

[Tom Fremont]

or by turning the sprocket over

 

 

Not on a 6-pot TR engine! ( it's offset )

 

Cheers,

Tom

[Guest ntc]

You can flip it.The dot should be on the outer of the sprocket.

Edited December 15, 2017 by ntc

[colin3511]

Hi Neil,

 

That's the problem. The dot is on the cam but the dot on the cam gear is pretty much on the same PCD. I was hoping someone had seen this before and would know how to fit it.

 

Any suggestions or is it time for the DTI?

 

Thanks,

 

Colin

[john.r.davies]

Here's the page from the Brown Bible.

 

 

As Tom says, there is no mention of turning it over, but why else would Triumph have gone to the trouble of providing two pairs of bolt holes?

 

The picture is rather pale (so is the page) and difficult to read, so, "check that marks A and B [on camshaft end and sprocket] coincide" and punch marks C [on rim of sprocket and on crank cog] line up" [with the centres of the crank and camshaft] Your's on the sprocket, Colin, as you have found, is in an equivocal position, leaving you in doubt as to where it should coincide.

 

My suggestion is to use Equal Lift On Overlap to check the cam timing, as used on the other side of that page!

I'll scan that if you wish, Colin, but I hope you have, or will aquire, your own.

Best thing to buy, after your car, of course!

 

John

 

[DaveR]

I agree with John's feedback. The 1.6 and 2 Litre ST workshop manuals state the cam cog can be turned over to obtain more adjustment. This is a common process on all the six and small four cylinder engines.

As is rocking the cam either side over the peak to centraliser it.

 

Dave

Edited December 16, 2017 by DaveR

[colin3511]

Hi John.

 

Thanks for the info. Again I have this but it doesn't coincide with what I have. The photo I posted isn't that clear but hopefully you can just make out the dot on the cam and the dot on the sprocket. I am probably being a bit dim but can't work out if the photo shows it in the correct position or if I need to turn the sprocket.

 

Thanks,

 

Colin

[Guest ntc]

Colin

That dot should not be there,sombody else has done that,do you know if it is a std cam?

[TriumphV8]

Colin, you are on the safe side if both

valves lift on overlap TDC same height.

 

As you may not have TDC marked now

and miss the pulley maybe its now the

right moment to mark true TDC to align

marks on the cover with the pulley later.

This will also give more precision when

setting the ignition.

 

I always find and mark TDC on the flywheel and back plate.

Its mostly not correct what the pulley tells.

[BlueTR3A-5EKT]

I agree with John's feedback. The 1.6 and 2 Litre ST workshop manuals state the cam cog can be turned over to obtain more adjustment. This is a common process on all the six and small four cylinder engines.

As is rocking the cam either side over the peak to centraliser it.

 

Dave

You can flip the sprocket on the simplex or single row chain type installation ie 1600/2000 Vitesse GT6, Spitwad/Gerald/SC but not on the duplex or double row chain type installation, which TR5/6 use. NB - I have deliberately ignored TR250 here as the parts book suggest the TR250 had both simplex and duplex chain installation, but no given engine no change point.

 

The ability to flip the symetrically shaped single row chain wheel enables up to 8 possible different timing positions. [bleeddin' obvious I know]

The double row duplex type cam chainwheel of the TR5/6 is not symetrical, as one side is deeper recessed than the other. - Giving only 4 options for cam timing.

 

(Question - Is the TR5/6 crank chain wheel symetrical, could that be flipped to gain more timing options)

 

The wet liner 4 cyl TR engine has symetrically shaped double row timimg gear on the cam which does allow for flipping - perhaps that fact has got sucked into TR5/6 engine building myth.

 

Peter W

 

 

PS Flip means turn front to back.

Edited December 16, 2017 by BlueTR3A-5EKT

[ed_h]

The replacement double row cam gear on my TR6 was flippable. It wasn't a special part--just a standard replacement from one of the big 3 (in the US).

 

Ed

Edited December 16, 2017 by ed_h

[Guest ntc]

Ed

Indeed

[DaveR]

I never trust the dots as I have found in the past they were out. So I always go back to basics and set-up the TDC, If this is out then re-mark it. The same with the cam, rock the cam and if it out re-mark it.

I spent a time in QA sorting out problems, it get in the blood!

 

Basically if you haven't checked the dots for yourself then don't trust them.

 

Dave

[BlueTR3A-5EKT]

The replacement double row cam gear on my TR6 was flippable. It wasn't a special part--just a standard replacement from one of the big 3 (in the US).

 

Ed

I must be remembering incorrectly

[john.r.davies]

I'm grateful to the Faculty of TRRU!

Some can be flipped, some can't.

 

Doesn't help Colin though, who has a weird sprocket.

Crank to TDC on No.1 (If the bellhousing is off, there may be TDC mark on the flywheel already.

Cam to equal lift on both valves on No.6. (See below)

Bolt up sprocket - if you need to, try either pair of holes, one may fit better, and 'flipping' if you can.

 

John

PS ELOO is best done with Dial indicators, but a very good approach is to put the cam shaft with both No.6 valves on the back of the cam, no lift at all.

Set the rockers so that there is a gap of 120 thou.

Now turn the camshaft until you see the exhaust falling at the same time as the inlet starts to rise (overlap).

adjust the camshaft until the gap at each is the same (equal lift)

That sets your cam timing.

[Guest ntc]

To be fair to Tom and Peter they are right,but? the old sprockets and chain will be worn out , always fit new best of both worlds.

[DaveR]

I agree fit new parts, as long as their not repro, and then start from square one.

 

Dave

[DaveR]

Peter, No flip option given in the PI handbook. I think you are right. I guess my memory is wrong.

 

Dave

[colin3511]

Really appreciate your replies. I am convinced the engine has never been touched from new. It has only completed 63,000 miles. Original bearings, piston etc. No need for rebore and only a crank polish fitting standard size bearings and TW's. The body and chassis were also totally original without a weld in sight. That reassures me that the timing marks are correct. I have lined all the marks up and it all fitted perfectly. The cam was reprofiled to give 280 degrees duration and 0.405 lift.

 

If everything is correct when would I see full lift on number 1 inlet? Head is off so I can clearly see the cam lobe. New chain and tensioner have been fitted.

 

I'd like to double check visually.

 

Thanks,

 

Colin

[John L]

This may help but is for the 4 cylinder TR engines and flipping the gear

https://www.bing.com/videos/search?q=cam+timing+for+triumph+tr4&view=detail&mid=E8651700B9C4567A17BCE8651700B9C4567A17BC&FORM=VIRE

[ed_h]

Come to think about it, there isn't even a need to flip the cam gear. Just using the alternate pair of mounting holes gives a 90 degree rotation, and thus a 1/2 tooth offset.

 

Ed

[Tom Fremont]

The duplex sprocket allows (2) positions, not (4) as having an even number of teeth (2X crank sprocket ) means the 180 degree positions are identical.

 

However... there are at least 3 degrees of slop in the holes so the adjustability is theoretically infinite . My habit is to wind them backwards when fitting, ensuring the chain is tight in the direction of rotation and set them 3 degrees advance of their nominal values to compensate for wear in use, which can amount to 6 degrees @ crankshaft on worn components if not more.

 

Another thing: the range of clamping from min <->max torque and degreased vs. oiled interface between the cam and sprocket is at least 2:1. We don't ever want the bolts to go into shear ( because they'll fail if they do ) so I degrease the interface, oil the bolt threads and tighten to the maximum recommended value.

 

Cheers,

Tom

[ed_h]

On my '74, the cam gear has 42 teeth, so each tooth represents about 8.6 degrees of rotation. Rotating the gear 90 degrees (by using the alternate pair of mounting holes) turns the gear by 10.5 teeth, or, since all teeth are identical, it effectively advances (or retards) the gear by 1/2 tooth. This means that we can theoretically only set cam timing in increments of 1/2 tooth, or about 4.3 degrees. In practice, there will be a little slop in the mounting holes as Tom mentioned. On my car the slop wasn't even close to 3 degrees, but whatever it is, it can offer a little additional flexibility in setting cam timing.

 

Ed

Edited December 16, 2017 by ed_h

[Guest ntc]

The cam was reprofiled to give 280 degrees duration and 0.405 lift.

 

 

Why? you had a Cp cam no?

Edited December 16, 2017 by ntc