Hi guys, spoke to Jeff this morning, what a helpful and knowledgeable chap, I'll no doubt be calling on his services before long.

 

Anyways, the upshot is that I think I have a cam timing issue. There is some confusing info on here regarding which marks to use when installing/timing up the belt etc which is why I'm having to ask this question. If I just go by the info in the manual, the passenger side cams are both retarded by a tooth, I haven't got around to removing the driver side and lower covers yet (it's raining :( ). This is assuming that the sprocket marks should align with the index marks on the backing plate.

 

I've attached pics (excuse the quality) of the intake and exhaust cam sprockets with the crank pulley set to 0 degrees. As an aside, you can see in the second pic how far advanced the CAS position is to get 15 deg BTDC - this is what started the alarm bells ringing.

 

If someone could clarify for me it would be much appreciated. I've always avoided touching cam belts but I suppose it was inevitable :(

 

 

you line up the marks on the cam belt only the marks on the back plate are for ref only

Jeff did a very good guide on here some where that explains it very simpley

I agree that all the info states to use the cam belt marks when installing a new belt but that's not what I'm currently doing, I'm trying to check whether the old belt is correctly fitted - hopefully without removing any more covers...

If the back plate marks are for reference, what reference are they for if not to confirm that the cams are correctly timed in relation to the crank ? (regardless of belt position).

Cheers

H

To correctly time up you will have to have the bottom crank mark lined up in its

correct postion this is vital as its so easy to put the belt on and don't notice that your one tooth out so if you want to check all the bottom cover needs to come off

How I would check would be top ref points bottom crank mark timing belt and if

it all lines up

 

Your pic shows your one tooth out but its the bottom mark that is most important in relation to how many teeth between each mark on the crank pully's

 

Im sure Jeff will be along some time soon

Ok, thanks. I've assumed that the 0 deg (TDC cyl #1) timing mark on the lower front belt cover, when lined up with the crank pulley index mark, will be the same as lining up the lower sprocket with its index mark - I can't see any logical reason for Nissan to not match this to TDC, but Nissan are full of surprises :-\

 

I guess this confirms that I need to go a bit further, pull the crank pulley and the remaining covers and start counting teeth etc... bah!

 

Cheers

H

Ok, thanks. I've assumed that the 0 deg (TDC cyl #1) timing mark on the lower front belt cover, when lined up with the crank pulley index mark, will be the same as lining up the lower sprocket with its index mark - I can't see any logical reason for Nissan to not match this to TDC, but Nissan are full of surprises :-\

 

I guess this confirms that I need to go a bit further, pull the crank pulley and the remaining covers and start counting teeth etc... bah!

 

Cheers

H

 

TDC marks are the same but if the belt is a tooth out you will not be at TDC

:no:

Also the timing marks on the belt will never line up again with the marks on the sprockets, could take several thousand revolutions, so best strip it and start again.

Not sure about that Andy, TDC is relative to the piston positions and fixed to the crank therefore belt and cam positions have no bearing on TDC. Unless I've misunderstood what you're saying.

Cheers

H

The timing marks do need to match up with the marks on the back plate on all 4 cams, assuming you do have it set at TDC

Not sure about that Andy, TDC is relative to the piston positions and fixed to the crank therefore belt and cam positions have no bearing on TDC. Unless I've misunderstood what you're saying.

Cheers

H

 

your forgetting the belt is the most importent thing to keep top and bottom

in sic so as I said the marks on the back plates are ref only the timing marks

on the belt are to keep cams and crank timed check out Jeffs write up with pics very easy step by step

 

If it was me I would get TDC on crank then take the belt off and set top end

not forgetting bottom crank can move if top sprocketts are not fixed I use as Jeff does small long nosed spring clamps so when the belt is moved the the belt can not move out of the groves but if your doing this check all tentioners

might as well do a comp sevice

There you go

 

http://www.300zx.co.uk/forums/showthread.php?t=135139&highlight=cam+belt

Ok, the belt was out by one tooth at the crank (i.e. all cams were 1 tooth retarded!). All back together and power delivery is much stronger, popping on the overrun has stopped and idle is steady.

 

The very odd thing is, having checkd the ignition timing the CAS is STILL at maximum adjustment to get 15 deg advance!? It was this that prompted me to check in the first place. Temperature doesn't go over 75 degrees either, I'm sure it used to reach about 82?! Anyway, Consult is expecting 15 degrees BTDC at that temperature so that isn't the issue...

 

There are a couple of other anomolies as well so I need to do a bit of investigation.

 

Cheers for the help

RobH

did you check timing with a strobe light or are you looking at what consult is showing ?

Yes, I use a strobe on cyl #1. I've got a spare CAS so I might put that on, I don't really see it as being a CAS problem but it's worth a try.

Cheers

H

Switched CAS with a spare one and it's much more central now, looks like a dodgy CAS.

 

Very strange that the temperature won't go above 75 though, after a long run it was reading 71 ?? Perhaps time to test the ECU temp sensor, it's only a few years old though and was working fine a few weeks ago.

 

Cheers

H