Adjustable timing sprockets

[miked]

I have the QED ones. Do you need to Loctite the little Allen stud threads that secure the timing position or just tighten them..??

Mike

[john.p.clegg]

Mike
Mine are just tightened and are still there after five years,,,

John

P.S.
Try not to drop either the allens or cup washers down the front cover,theye are a bugger to retrieve....

[miked]

Thanks John,

Know what you mean, I was paranoid when putting them in there. Very easy to drop.

Mike

[martinbrowning]

Mike,
Do these make an appreciable improvement to the running of a standard road twincam? I know that Miles Wilkins doesn't mention them and just wondered whether they were a worthwhile investment. By the way, how much were they?

regards

Martin B

[john.p.clegg]

Martin
Sorry to but in but they make timing the cams a lot easier and if you wish you can then play with adjusting the cam timing to suit you..

John

[martinbrowning]

John,
No apology needed- please butt in! You see so much about adjustable cam sprockets and I welcome your thoughts.

Martin

[miked]

Martin,

John is right. When I built the last engine I did the off set dowels. First for me!
It is a fiddle when lining up the PCD of the dowel. Also have to claculate and order dowels and wait. For a part timer like me the adjustable sprockets are great. I think they are about ?90.

Regarding the benefits. Others on here will be able to say better than me. All I know is that I want the best I can get. Have had everything balanced and the head reworked etc. I want the valve timing dead right for maximum performance. Wilkin's book mentions little point on a standard motor but of more benefit on tuned motors.

Mike

[rgh0]

Maximum cam timing error possible without using offset dowels or adjustable sprockets is 10 crankshaft degrees, if more than 10 degrees you can get closer by swapping to the next tooth on the sprocket.

Loss of power on a standard big valve sprint spec engine at this degree of error is approximately

Inlet
+10 degrees (advanced) = minus 11 hp
- 10 degrees (retarded) = minus 3 hp

Exhaust
+10 degrees ( advanced) = minus 6 hp
- 10 degrees ( retarded) = minus 2 hp

If exhaust and inlet both +10 degrees (advance) = minus 13 hp
Losses are aproximately linear with increasing error

These are based on my twin cam simulation in the Dynosim program which gives good results on cam timing and design changes. If you have an error in timing keep it on the retarded side as this minimises the losses.

13 hp is about a 10% loss and says using offset dowels or adjustable sprockets warranted in a road engine if your at the worst case timing error of 10 degrees advanced from the 110 degrees MOP standard spec.

Most engines these days are well away from the standard cam timing if using straight dowels in the standard sprockets due to worn chains, worn sprockets, skimming of heads, varying gasket thickness and line bored blocks so doing it by the lines on the sprockets is more hope than science.

regards
Rohan

[john.p.clegg]

Just a stab in the dark here as I'm no expert (not even close) but I'm sure i read somewhere of altering the cam timing a little to increase the power,or was it torque,or was it move the power,or was it torque......

...Told you I was no expert...

John

[rgh0]

Reducing cam overlap by advancing the exhaust and / or retarding the inlet cam will generally increase mid range torque at the expense of top end power. The size of the change depends on the cam profile and recommended overlap you are starting with. Normally only considered for competition cams with a longer duration and large overlap specification that were aimed at maximum power at high revs and where you are trying to get a better wider power band to suit a particular application. Makes little difference for the standard sprint cam as overlap is relatively small to begin with.

cheers
Rohan

[john.p.clegg]

Nice one Rohan,I knew someone would come up with the goods...

John

[Midlife]

I reckon the verniers the way to go... whilst waiting for my dial gauge I took the cam cover off and checked the marks lined up on the cam sprockets at TDC, and they didn?t... the inlet was retarded by one complete "tooth". so I lined them up and re-tensioned the chain. There was a noticeable, in fact big difference in all areas... pick up, torque and revs better/higher. So I will definitely be getting vernier sprockets and timing the whole lot in?

[JATLAN4]

The usual problem with adjustable spockets is where can you get good quality ones? No decent quality in UK - any suggestions. But unless you are regularly changing camshafts is it simpler and more reliable to use off set dowels ? Any thoughts?
John

[john.p.clegg]

QED are O.K. by me

John

[rgh0]

I have always used offset dowels. I bought a set from Dave Bean about 20 years ago with 2 dowels each at 1 degree intervals up to 10 degrees. Relatively cheap and suffiicent to keep my 3 assembled twin cams in the right cam timing over the years.

The timing with off set dowels is a bit harder to set up versus a adjustable sprocket set and you cant change timing at the track quickly and easily as you can with adjustable sprockets but those disadvantages are minor.

A friend recently got a set of Burton adjustable sprockets which have performed OK in his car for the last couple of year.

cheers
Rohan