CMax03

iTrader: (3)

I'm having some issues with my built VG30 eating timing belts.....The first failure was more less a bent tensioner stud that wasn't properly torqued to spec causing the tensioner to bend the stud and walk off toward the block and pop!!! Well just yesterday coming home from work my car 's timing belt popped and of course bent some valves.....I'm running Isky Cams with .425" of lift and maybe the cams are stressing out the belt causing premature failure....I'll be rechecking the end play of the crank and cams as well as the trueness of the sprockets to each other....any suggestions guys? I found this site that might have a remedy for my problem.....Any other Cammed VG's out there?

http://www.importpartspro.com/poensustiivg.html

ajm8127

iTrader: (8)

This is precisely why I like timing chains. Higher lift cams would compress the springs more and that takes more force. I've read that the net effect is zero, however, due to some valves opening and some closing. It is a net effect, so in a DOHC engine, there would be an imbalance of force between intake and exhaust sprockets on a given head.

I think checking the end play and sprockets are a good starting point. I'd also look at the belt. Is it a clean break, like the max tensile strength of the belt was exceeded? In the end, the stronger belt looks like it might be the way to go.

SteveB123

iTrader: (2)

Check for coil bind.

CMax03

iTrader: (3)

Well guys I've been busy with an occupational change and not alot of free time to do anything with my 1990 Maxima and it's 2nd timing belt failure...I removed the timing cover today/yesterday and found a section of about 4-6" of cogs missing on my belt....The alignment was good...looks like during moderate acceleration the engine sheared the timing belt cogs right off.....MAYBE I wasn't tight enough which I measured the tension in accordance to the Maintenance manual.....It was a brand new NAPA belt.....Maybe I'll go and upgrade to a 93-94 VG30 cam sprocket/crank sprocket design (round) and belt which is stronger than the 89-92 VG30 designs....Maybe the extra power and torque just cut the cogs right off!

Chris Gregg

iTrader: (59)

I have Schneider cams 280-70H set; aggressive grind. Gives my turbo a nice little lope at idle! Also have their valve spring set.
Cmax, if it was anyone else I'd say it was a bad install. But you're too OCD and have a good understanding of these cars.
Before your last post I was going to ask. Which sprockets you are running. I swapped mine over to the round tooth. Much more confident and have no concerns revving into the 7k+ rpm range. Definately right direction in your situation. BTW, which valve springs you running?

Chris Gregg

iTrader: (59)

Just to share some knowledge, the FSM dictates how many teeth on the belt should be between each cog. I've rotated my crank after timing belt changes to discover the belt on the crank to begin trying to skip a tooth. I found this seemed to only happen when the number of teeth are off, just by one.
I say this as something else us OCD guys can be mindful of. Also because this is the only other scenario I can imagine at this hour which might ultimately rip teeth off a belt.
Believe it or not, I've seen cam sprockets rip the alignment nipple right off the cam and crack the end of the cam. And yes, I have pics.

Matt93SE

iTrader: (44)

I'd hate to point fingers at random crap, but what's the quality of a NAPA belt? Only timing belt I'd trust is OEM or Gates. but that's just me.

also, were there any 'compounds' used when assembling the belt? i.e. did you spray anti-sieze or brake cleaner or anything like that onto a cam sprocket or anything? I wonder if a fluid of some sort might have attacked the belt chemically so that it failed in that section. (The FSM mentions to not even get antifreeze on the belt..)

as for the timing 'trying to be off a tooth', I'm not sure how that's an issue since all of these sprockets and gears rotate independently of each other. maybe at TDC with all of the springs seated as much as they're going to seat, they're 1/2 tooth apart.. I've seen that before, especially with high lift cams.
But once you get the belt on and properly tensioned, they stay in place just fine. when the engine is running, there is ALWAYS some drag on the belt so that issue is again moot.

vernk

could it be possible that you tighten it to much causing the belt to stretch to much??

CMax03

iTrader: (3)

No I'm sure I used a spring scale to set my tension/allowed play as per the manual....Normally belts that are too tight moan like hell and this was quiet and running awesome....My timing was quadruple checked by hand with 3 x 720 degree revolutions before firing....I thought that the NAPA belt were GATES! But I 'll switch over too the round tooth sprocket design and their more durable designed timming built with kelvar composite compounds....No Matt I didn't spray the belt with anything...Normally after I spray I blow everything off anyway.....I think I got a bad belt this time and I'll try it again ....I'll upgrade to some JWT Hi rev springs and ARP headstuds while I'm in there again! Thx for all your suggestions guys!