Cam timing question

[stuartgb100]

Dave,

A question..........

If building the engine from scratch, why cannot the cams be statically timed correctly from a timing disk on the crank (eg) before the engine/dyno testing ?

Is the dyno engineer trying to improve on the cam manufacturer's settings when he seeks to change the timing to achieve more power, or corect the engine builder's settings?

Regards,
Stuart.

[tdafforn]

Welcome Dave,
I think Dave's comment in the previous message sort of explains. In general you would aim to get the cam timing correct on a rebuild. However you often need the use of adjustable sprockets or offset dowels. In this case (and correct me if I am making a fool of myself, I usually do!) these were not an option, hence the non-opitimal timing. eventually one of the rolling road guys tried to adjust the timing by modifying the sprocket, but it is obviously a sight more difficult when the engine is in the car!
Cheers
Tim

[SimonH]

You would, ordinarily, set the cam MOP correctly while the engine is in build. It the correct way to do it and gives the most consistant results if done properly. I have done loads of cam timings this way when I was a powertrain tech building engines and running engine dynos. It is the best way as far as I am concerned.

The lift at tdc method is a more convenient way of doing things when you cant get a direct veiw on the front pulley area, ie. when the engine is in the car.

If you try to set the cams by MOP and you are at too much of an angle there is little chance of getting it correct. The lift method cancels this out.

The dyno operator will be trying slightly different settings to give tweaks to the engines output by changing the overlap etc. Although the settings at MOP will be correct there may be a slight advantage to be had by adjusting the settings depending on the overall spec of the engine.

As Rohan has said rolling roads are fraught with errors due the varying conditions in the test area. They are great as tuning tools so you can see gains and losses but I wouldnt take the numbers provided as gospel. They are a good indicator but thats about it.

[types26/36]

You would, ordinarily, set the cam MOP correctly while the engine is in build. It the correct way to do it and gives the most consistant results if done properly. The lift at tdc method is a more convenient way of doing things when you cant get a direct veiw on the front pulley area, ie. when the engine is in the car.Although the settings at MOP will be correct there may be a slight advantage to be had by adjusting the settings depending on the overall spec of the engine.

I agree with Simon and this is the way I have always done it but can see the that under cirtain conditions the TDC lift method would have its avantages partically for the dyno operator.
As for the saga of the rebuild there are always two sides to a story and I'm glad that Dave has put his side forward.
I echo Stuarts comment, stick around Dave we really are'nt such a bad lot.

[stuartgb100]

Okay,

The question I was trying to solve was:

With the engine out out of the car, being totally rebuilt, with some new and some refurbished parts being used ............ why could the cams not be set up correctly ?

Personally, have never used vernier sprockets. Just order in the offsets required.............. Not happy at all about filing away at existing dowels either. WTF ?

Am in the building trade (sad).

Have to say that best recent laugh was the sight of a van with the sign:

"Bodget & Scarper" ( that's their spelling of "Bodget"")

Regards,
Stuart.

[stuartgb100]

Okay,

The question I was trying to solve was:

With the engine out out of the car, being totally rebuilt, with some new and some refurbished parts being used ............ why could the cams not be set up correctly ?

Personally, have never used vernier sprockets. Just order in the offsets required.............. Not happy at all about filing away at existing dowels either. WTF ?

Am in the building trade (sad).

Have to say that best recent laugh was the sight of a van with the sign:

"Bodget & Scarper" ( that's their spelling of "Bodget"")

Regards,
Stuart.

[types26/36]

Stuart, when I said "echo" I didn't mean it literally

[stuartgb100]

Brian,

Let's hope Dave will go with the echo...........

Regards,
Stuart.

[john.p.clegg]

Dave
Many thanks for the reply,but two things bother me....

1) I honestly can't recall ever seeing TDC figures for any cams ( not being in the trade I may be showing my ignorance)

2) without knowing exactly which cam you are dealing with ie an engine turns up with cams in it,how do you know the TDC lift?

Many thanks

John

[davewalker]

Major cam manufacturers quote cam timing figures both ways, ie "full lift @ *** degrees" and "lift @ TDC" - the latter for the benefit of the rolling road tuner. As I stated previously see Kent, Piper etc cam data info.

Cam timing adjustments can make significant changes to the characteristics of an engine, particularly DOHC types. QED, for example quote different cam timing figures for some of their cams to suit different applications. Good dyno operators will swing cams to optimise performance characteristics to suit the application.

When Lotus built Chris Hewitts TC, they didn't time in the cams. When I rebuilt it I didn't - please go back and read my original post.

Whenever I fit hotter cams in TC engines I use vernier pulleys (I hate offset dowels, OK in X'Flows but not for me in TC's). From now on, all my TC rebuilds will get verniers, too hell with the cost if this is the response you get. Read my original posting - and note the cost.

PS, I am starting to get bored!

[redskatejbf]

Davewalker....... Dont get bored, with you and Rohan posting this site will be absolute magic. I`am sure very few people on this site were aware of checking cam timing at T.D.C. A lot of owners will now be asking there suppliers for that data including me.
Please keep posting.
Regards John

[kenny]

Thicko question coming up. On an old 40 year old twink who would give you the figures of what lift the cams should have at TDC?. I bet if you checked similar spec cars each and every reading would be different.
The modern cams I've used on K and Vauxhall applications do indeed give these figures..........but a 40 year old engine with 2 foot skimmed of its head and using whatever cams old Chapman had in stock is a struggle.

As I said, if my SE motor after my rebuild were to give 85 @ wheels I'd get truly pissed and hoover up for the Mrs for a week.

Kenny

[tower of strength]

Welcome to Elan Net Dave, what would you charge to convert a standard valve head to unleaded?

regards

Mark

[rgh0]

Kent Cams quote lift at TDC for their CPL2 camshaft which is the same timing and lift as a orginal sprint camshaft at 1.80mm (0.071inch)inlet and 1.72mm ( .068 inch) exhaust. The difference in the lift at TDC is due to the different valve clearances on the inlet and exhaust cams. The .065 inch setting measured is close enough for a road car with a standard setup and should have the cam timing correct to what possible without verniers or offset dowels of a few degrees.

While you can set the cams at TDC using this method and its OK for a quick check for gross errors with the engine in the car it is not as precise at setting it at maximum lift point. This is because small changes in valve clearance affect the reading plus the cam is ramping up fairly rapidly at this point and small errors in cam grinding and in doing the lift measurement also can have a signficant affect on the setting.

I have made myself small diameter timing wheels that fit on the cams so i can do a more accurate timing check and adjustment with the engine in the car.

Building a twin cam that works well on a tight budget is a trying experience for both the builder and the owner as you have to make many hard decisions on what you do and dont do. Its easy in once sense to build a $15000 race engine as you just do everything and dont worry about the cost. Doing a road engine is actually harder as you invariably have to make some compromises.

The aim of this forum is to understand and help people with their problems, sometimes this raises questions about the quality of work done or approach taken by an owner in getting it done but we should all be careful to focus on the problem not the people - just my 2 cents worth

Rohan

[JJDraper]

As an 'amateur' engine builder, I have limited experience of the finer ponits of a build. However, I have done a couple of head gasket replacements. The last but one major head rebuild involved new cams, guides, buckets, unleaded seats etc etc. The cams are QED Q360 cams, and I was reasonably pleased with the performance compared to the old anonymous cams. After 35k miles, the head gasket went (+60 pistons mean there is a weakness there) and I fitted a new one. This time round the engine is a completely different, rev happy beast. The only thing I can think is different is getting the sprockets lined up correctly this time round. Performance is up, but fuel consumption got worse! Not sure if this is because I push harder now or whether the previous valve timing was more economical. Just goes to show that a slight difference in build variation makes a big difference in 'go'.

Jeremy