Why Does My Engine Insist On Re-tuning Itself??

[tas_ae71]

hey guys,

 

having 2 issues at the moment, car is 4ac kesev.

 

1. my cam timing seems to keep jumping a tooth (or two).

-belt is always kept adjusted tight has the spring on there and i leaver the bearing tensioner on a little more when nipping the bolt up to make it even tighter (not over tight).

-belt is probaly 40,000km's old and doesnt show signs of wear

-cam wheel and crank pulley don't really look worn. if they where then they would be chewing the belt out.

-valve springs are stock, cam isnt.

-belt appears to run true when motor is running and cam isnt bent or anything silly

-not 100% sure but may only be happening when i give it a heap of revs (i regularly give it some stick haha)

 

 

ANY IDEAS??

 

 

2. my tappets, or perhaps only one or two are noisey, i have adjusted them a few times now to the correct gap specifed under the bonnet.

-when i start the car after being adjusted they are relatively quiet. after being driven (perhaps revved hard).

-that one or two tappets will be quiet noisey as they are again at the moment. it almost sounds like a spun bearing at the moment (its not as if i adjust them it will go away)

-I'm probaly doing them on the tighter side of things when i adjust them.

-also i have a reground cam but do not know 100% what the clearance is supposed to be for the cam so i just do them at what the standard clearance is.

 

ta

[Taz_Rx]

Your cam is like 270* or something isn't it?

You will need to have a slightly bigger valve clearnce for these, maybe chuck an extra 10-15% in.

Also remeber that most listed valve clearnaces are a HOT setting.

[styler]

hmmm sounds interesting... not sure but heres a few ideas

 

belt might be stretched or stuffed even if its only 40k

 

tensioner may be stuffed or not run properly when running

 

teeth on cam wheel/crank pully probably unlikely to be worn too much

 

valve springs stock could be a problem if the cam is much more aggressive than

stock, you may be getting some sort of valve float causing a slack in the timing system

which may allow the belt enough slack or shock to jump a tooth or two.

 

the bigger your cam the more problems you would have with it too, especially if reground

with a reduced base circle instead of hardfacing and reground but that probably affects

direct cam lobe drive on bucket setup more than a indirect cam on rocker arm setup.

 

belt running true / cam straight also sounds fine.

 

heap of revs = valve float, especially with stock springs even more with old factory ones

as they lose their tension over the years, with a cam a bit more aggressive i would at least

use new standard springs and a with a cam a lot more aggressive i would use new stiffer springs.

 

tappets i would say old valve springs will sag / reduce tension especially after heated operation may

stay a bit lower than when been sitting cold??

 

id call the cam place you got it from for clearance advice or any cam place really for some sort of direction on it.

Edited August 10, 2009 by styler

[tas_ae71]

i do the tappet adjustemnt hot as its ment to be done..

 

i did not buy the cam new, also it had done very little work, no signs or wear at all. so i cannot confirm the exact specs of it.

 

he said he thought it was 290 degrees, but he also told me it was a 35/73 (3500~7500rpm power range) which would surgest to me that its not quite that big in the duration..

 

as for the actual lift, i dummy fitted it to a old broken head to see how much extra lift it had compared to the standard cam, i gfound the standard inlet lobe has a fair bit of lift but the exhaust had FECK all. the reground cam has a fair bit extra lift in the exhaust and about the same on the inlet (no dial gauge to measure properly). taking to be tested on a cam doctor (if someone still have one in launceston?) isnt practical either.

 

 

so valve float is where when the cam is on the down ramp and the valve is closing, the soft tention of the spring means that the ramp falls faster then the valve spring can re-coil making the rocker go slack instead of keeping it tight against the cam lobe as it should????? thats what came to mind by what you said :lolcry:

 

as i said the belt doesnt show signs of wear and it quite tight, altho you maybe onto something with the bearing, i did notice that the face of the belt contact is a bit discoloured which means is been heating up and has picked up small spots of rubber off the belt. so you maybe onto something there...

 

ill go and check to see how free spinning the bearing is. but it must be fairly shagged to cause enough resistance to make the belt slip, the 4ac has a lot of teeth/wheel contact.

[tas_ae71]

have had to adjust timing twice since i made this thread!

 

i think I'm going to grab a new belt, i did not when i first start the motor and its cold, it sounds like its got a "mew". similar to that of a supercharger/gilmor belt drive.. after a few mins it goes away. could be coming from soemthing else other then the timing belt. perhaps from incorrectly toqued cam caps :P