4 replies to this topic

[DaveRob]

OK...... Timing cam in today.... 274 scatter pattern. Book says 108 degrees and got it measured at 106.25 degrees. Vizard says with a new chain set it at 1 degree retarded..... so do I set the vernier at 109 degrees or 107 degrees.... any other suggestions welcome.

Thanks in advance

Rob

[DaveRob]

Whilst waiting I found this nugget of info on the WWW.

When degreeing the cam, its possible that the cam may not always check out in the right place. For example, lets say you degree the cam in your engine and discover the intake centerline is actually installed at 112 degrees ATDC compared to the 106 degree specifications. This means the cam is retarded relative to the cam card spec. To position the cam at 106, the cam must be advanced 6 degrees. Conversely, if we found the cam at 103 degrees ATDC, this is advanced compared to the 106 centerline. Repositioning the intake centerline at 106 degrees ATDC would require retarding the cam 3 degrees.

Theirfore substituting my numbers in

if we found the cam at 106.25 degrees ATDC, this is advanced compared to the 108 centerline. Repositioning the intake centerline at 108 degrees ATDC would require retarding the cam 1.75 degrees PLUS visards 1 degree making a total of 2.75 retard. But taking the first part of the info

you degree this cam in your engine and discover the intake centerline is actually installed at 112 degrees ATDC compared to the 106 degree specifications. This means the cam is retarded relative to the cam card spec

I see that 112 ATDC is retarded value compared to 106... IE bigger degrees = retard.

Theirfore I should time for 109 Degrees........

I would appriceate someone confirming mty thoughts on this one tho

Thanks

Rob

[tommy13]

I've been puzzling over what you have said about Vizard's advice and it doesn't make sense until I had a look at my copy to find you have misread or misunderstood what he actually says.
" with a new chain, it is a good idea to set the valve timing 1 degree advanced, so as the chain wears it will soon become 1 Degree retarded."

In your case 1 degree advanced will be at 107 degrees ATDC. With a reading of 106.25 I would be inclined to leave it at that.

[DaveRob]

Durrr........ Thank you...... missread visard... after re reading all made sense.... got it to 107 degres now..... on with the build

Rob

[mini7boy]

OK...... Timing cam in today.... 274 scatter pattern. Book says 108 degrees and got it measured at 106.25 degrees. Vizard says with a new chain set it at 1 degree retarded..... so do I set the vernier at 109 degrees or 107 degrees.... any other suggestions welcome.

Thanks in advance

Rob

it doesn't make sense to me that Vizard would recommend that the cam be installed with retarded timing. The usual recommendation is for the cam to be installed with advanced timing so that a wearing/stretching timing chain will cause the timing to come to near spot-on. If you install it retarded, it will only become more retarded with chain stretch.

checking Vizard's TBASE, 3rd edition, page 337, rightmost column, Vizard recommends setting the timing one degree advanced and then says ".......because it won't take long for the chain to wear sufficiently to retard the cam by 1 degree".