Cam sprocket hole alignment

[alan_thomas]

Just replacing chains after rebuilding engine and with the No2 piston at TDC (measuring with DTI and know it to be correct) and cam correctly aligned the cam sprocket mounting holes are out.
The heads have had a light skim which should change this by a small amount and as far as I can see it makes no difference to the alignment which way around either the Camshaft or Crankshaft sprockets are fitted as they are symetrical. Both sets of sprockets are new and could be drilled incorrectly compared to the position of the teeth.

I have the equipment to accurately redrill the sprocket holes to match my timing but I wondered is this a problem everyone faces and do rebuilders accept the cam timing is out by a few degrees? or do what I am probably doing to do, remove the sprocket and redrill a pair of holes that correct the timing. Alan

.DSCN3164.jpg

[V Mad]

I have not come across this Alan. It looks a long way off from the picture. Have you compared the new sprocket with an old one just to check that holes are wrong and its not something else? I cant understand why they would make something that inaccurate.

[DJT]

Hi Alan,

Check the alignment of the bolt holes with the teeth. Correctly drilled sprockets have the holes aligned with the point of a tooth. There are some about with the holes aligned with the valley between two teeth.

This is illustrated on the LDparts website: http://www.ldparts.co.uk/shop/shop.p...6860d6260ea912

If you have the gear to re-drill, it may be worth doing.

Dave

[alan_thomas]

Dave I was aware of the holes lining up to the top of the tooth and check both the new sprockets and they do point to the top of the tooth and not the root so its a pity I haven't got the 'incorrect one' as half a tooth would be spot on. Have rechecked everything and its still the same way out so it looks like I will have to redrill. - Alan

Hi Alan,

Check the alignment of the bolt holes with the teeth. Correctly drilled sprockets have the holes aligned with the point of a tooth. There are some about with the holes aligned with the valley between two teeth.

This is illustrated on the LDparts website: http://www.ldparts.co.uk/shop/shop.p...6860d6260ea912

If you have the gear to re-drill, it may be worth doing.

Dave

[martin]

Just a thought Alan, have you got the chain slack on the wrong side ? Martin.

[alan_thomas]

Just a thought Alan, have you got the chain slack on the wrong side ? Martin.

Martin I always keep my chain tight on the right side! Chain tight on straight run with a 1mm gap behind the tensioner - Alan

[StagnJag]

I seem to recall 'Flying Farmer' Neil coming across this before, so it isn't unheard of.

Rgds

Dave

[Stagdad]

I seem to recall 'Flying Farmer' Neil coming across this before, so it isn't unheard of.

Rgds

Dave

I was thinking I saw it from Neil a while back.

Cheers Steve

[flying farmer]

This is a regular problem if you are careful with measurement when rebuilding an engine. From the look of the alignment on that photo, it looks more or less half a tooth out.
The best way to do this is to redrill the holes at more or less 90 degrees to the old ones so you are using the undrilled section of the sprocket, rather than oval the existing holes. To ensure everything lines up try mounting a pair of sprockets on a drill shank, I think it is half inch
When you decide just how much movement is needed rotate the sprockets the correct amount, ie if you need half a tooth, put the tooth of one sprocket so it lines up with the valley of the other, then you can use the holes in one sprocket to give an aiming point for a dot punch. This way you will get the holes in the right place.
Be carefull if you want one third of a tooth because it is very easy to go the wrong way and end up with two thirds of a tooth instead, and turning it back to front doesn't help. No prizes for guessing how I found this out!
I always try to set the timing one or two degrees advanced so that as the chains wear and stretch the timing becomes more accurate. IIRC one tooth is 9 degrees
Head skimming and chain wear both retard the timing, and I have rebuilt more than one engine where the cam timing has been one tooth out, probably because the engine builder has simply aimed for the nearest hole in the sprocket
I am glad you have used a dial gauge for finding TDC as I have found one engine to be 4 degrees out compared to the timing marks.
I really ought to trawl my photos and post something in the technical section
Neil

[stagmuffin]

this is what you want ,

http://www.ebay.co.uk/itm/250905385605?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

[Bob Heritage]

this is what you want ,
http://www.ebay.co.uk/itm/2509053856...84.m1423.l2649

There you go- only £141.80 each, cheap as chips

[alan_thomas]

Just come back from the garage, just the inlet manifold to go. In the end I redrilled the sprockets and got everything spot on. On just reading Neil's post I did it in a similiar way, used the bolt/shaft that normally goes thru the sprocket to locate it onto the cam to bolt 2 sprockets together and offset them by the amount I needed then driled thru with a 7mm slot drill on my mill. This has the advantage that using the hole from one sprocket to locate the correct place the slot drill doesn't need a centre.

Steve, at £143 each I thought hard and a split second later thought new holes would be cheaper!
- Alan

[stagmuffin]

Just come back from the garage, just the inlet manifold to go. In the end I redrilled the sprockets and got everything spot on. On just reading Neil's post I did it in a similiar way, used the bolt/shaft that normally goes thru the sprocket to locate it onto the cam to bolt 2 sprockets together and offset them by the amount I needed the driled thru with a 7mm slot drill on my mill. This has the advantage that using the hole from one sprocket to locate the correct place the slot drill doesn't need a centre.

Steve, at £143 each I thought hard and a split second later thought new holes would be cheaper!
- Alan

well done al
steve

[dasadrew]

Does Peter at LD sell the holes?

[KOY 23]

Does Peter at LD sell the holes?

Yes but unlike drills the bigger ones are cheaper.