: 2005 Bonneville GXP Northstar jumped time

11-19-13, 07:01 PM
Just snagged up a 2005 Bonneville GXP for a very good price, previous owner only had it for three weeks, he bought it thinking he could fix it but decided to sell it instead. Long story short it died and nobody bothered to really look into it, just sell it instead. I picked it up with the belief the engine was shot and likely part the car out, but figured I would investigate first.

I found that the front timing chain tensioner had broke allowing the timing to jump at least on the intake cam, possibly the exhaust cam as well. On the intake cam all eight cam followers actually popped right out of their normal place and were just laying around in the head.

My question is likely self explanatory, but I am curious as to just how much the timing can be off before causing damage from the valves hitting the pistons? I don't have the front timing cover plate off, but I did look up and see that the cam dots should be facing up 90* from the surface of the head, looks like one cam or the other is maybe two or three teeth off. I dont' see any dead giveaway for bent valves and I can't just slide the followers back in place.

I just want to make sure that this is for sure a dead engine that can't be fixed with a new tensioner and resetting the timing before I part out this car which is otherwise in very good shape.... I can triple or quadruple my money by parting it out, but I would rather fix and drive it.


11-19-13, 08:37 PM
You could stick a mechanic cam down the spark plug hole and look to see if the piston show signs of contact with the valves.

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11-19-13, 08:52 PM
Can't answer your question, but that's a very odd failure for a Northstar.

11-20-13, 09:34 AM
Not good. Use a borescope to see if the piston tops have been hit by valve(s). If any of those cam follower buckets looks dished or has a definite circular wear pattern that is not mirror-smooth, replace them. next to go is one or more cams.

Consider running a HD fleet or marine 10W-30 oil with its heavier anti-scuff additive package.

Here's your chain/timing mark setup. That crank pulley (serpentine belt) MUST be torqued to 37 lb/ft PLUS 120 degrees of tight. It drives the oil pump through clamping friction: Improper tightening sequence = no oil pressure.

11-20-13, 04:58 PM
An 05 gxp is a $8k car. Would be nice to fix motor. Or part it out. Not my car

11-21-13, 08:16 AM
#6 on that diagram is what broke, seems the tensioner would be able to take up the slack though, maybe that failed as well. I paid $1,600 for the car, $50 to rent a dolly to pick it up, $75 in gas and a roughly five hour total trip. It has 190,000 miles on it but most of it is in very good shape. I swapped a Northstar in an 04 GXP I picked up last summer and it was a terrible job in this car, absolutely no room anywhere. I would love to swap in a good engine just don't have that time to dedicate to it right now. My wife and I are actually tossing around the idea of taking the drivetrain out of her 03 SSEi and swapping that into the GXP, going to go over both bodies today to see if the GXP is much nicer then the SSEi and if it is the L67 swap would more then likely happen. The SSEi has 252,000 miles on it but the engine is solid as a rock and the trans was new (not rebuilt) 80,000 miles ago. The body is in amazing shape overall for the miles so it will be a hard sell lol.

11-21-13, 09:52 AM
Lots of HP info on grandprix websites. The 4t65 is $$$ to build up. Some have started swapping in the 4t80 into grandprixs and using the Buick V6. A few members have worked backwards and start with a bonneville since engine bay is bigger. Looks odd to see v6 mated to 4t80. Mostly cuz there is no NS style coolant crossover above trans bell housing.

11-22-13, 12:07 AM
If it were to happen it would have been an entire drivetrain swap, subframe and all, it has been done and documented at least once that I know of. Either way though, it wasn't meant to be. The GXP body just isn't in good enough shape / better enough shape then my SSEi to warrant a drivetrain swap. The GXP will be parted out and the parts will live on in other cars, including the wheels and doors on my SSEi.

11-22-13, 01:08 PM
A mistimed motor can damage all kinds of parts. And NS heads are not cheap

11-23-13, 10:11 AM
I am well aware of the damage that can come with an interference motor, I just wasn't sure how much slack there was as far as the timing being off before the valves hit. Doesn't matter anyway now, parting the car out. It is worth $4,000 - $5,000 just in parts and even in running condition only about $4,000 to sell it. I already have many parts stripped off it and cleaned up / polished to as close to new condition as you can get for some of them.

12-12-13, 04:46 PM
come to Canada that car is worth about 10-12 provided in good condition and milage isnt too high


PS we carry Brand new heads, send me a message for a quote