difference between ST and BT cam drive sprockets?

[matt dunn]

Is the cam drive wheel on the crank different between
a Silvertop 20V and a Blacktop 20V?

Here's what I found.

I line my engine up with the notch on the cam drive sprocket with the dimple on the oil pump housing like you are meant to do to do cam timing,
and the engine is not at TDC.

This is a Blacktop oil pump and a Silvertop cam drive.

With a Silvertop oil pump and a Silvertop cam drive,
the same marks line up and it is TDC.

The keyway is fine and in the correct place,
as when you fit the front pulley, the TDC marks on it are correct?

matt

[20v_rollaboy]

So with the BT oil pump, ST sprocket, and front cover fitted, the marks are correct on the cover? (with dimple and sprocket lined up)

Are the dimples on the oil pumps in the same place?

[matt dunn]

Are the dimples on the oil pumps in the same place?

I do not know, but I suspect it is not in the same place,
which would also mean the cam drive sprocket is marked in a different place in relation to the keyway,
meaning two different sprockets??

[20v_rollaboy]

Sorry I cant be of more help, Ive only ever dealt with ST's.

But I would say use the original sprocket and make sure the engine is at TDC by sticking something down the plug hole, and double checking on the sprocket cover.

[Mr Revhead]

i dont think matt is after help to time his engine

more trying to establish the exact difference between two parts

[matt dunn]

i dont think matt is after help to time his engine

more trying to establish the exact difference between two parts

Exactly,

So maybe Mr revhead can puch out some part numbers,

I dont have acess to a cam drive off a blacktop,
so want to know before I go and buy one,
if it will just be the same as the ST one,
or if it will in fact be slightly different.

Matt

[sergei]

From my experience with using ST sprocket on BT:
1) ST sprocket is skinnier (1 ~1.5mm thick washer seems to fix misalignment)
2) It is off by about half of tooth.

I assume it is off because of the difference in oil pumps.

I learnt it hard way as the performance was poor for no apparent reason, similar to blue-top, which the BT replaced, so after checking everything, I decided to do screwdriver test and figured that ST sprocket is off.
The reason why I used ST sprocket is that I have destroyed BT original sprocket in order to remove it to replace the seal (they have this habit of getting stuck big time), this all happened in weekend and needed car to be running ASAP so I resorted to ST sprocket.
Half of tooth makes huge difference in performance in those engines.

[Mr Revhead]

they are a different part number.

[85AW20v]

And aren't the timing belts different in length as well with the BT being 1 tooth longer?

[matt dunn]

And aren't the timing belts different in length as well with the BT being 1 tooth longer?

Yes, but that is in the tensioner location,
which is why i used a BT oil pump as it made the belt the right length,
where a ST one needed a little mod to get the belt right.

[slighty_sykotic]

Yes they are different.

I rebuilt a BT and like Sergi i had to use another pulley, as I destroyed my BT due to it being stuck.

Put a ST one on, lined up marks, put cam belt on. Engine started and idled ok, but it would rev really slowly. Like taking 3 or 4 seconds to hit high revs after going wide open throttle (just in neutral).

Put belt off and on a few times, until I decided to check the marks with a screwdriver, and sure enough, was a tooth or two out (can't exactly)

[matt dunn]

Mine ends up exactly 1/2 was between teeth.
Anyway, make enough power as is,
so adjustable cam wheels can be next seasons project.