: Internal Engine Questions!

04-19-11, 03:07 PM
Well after a blown radiator, blown heater core, having to replace all the hoses...and the water pump....(yeah, I'm a slow learner)...I finally figured out that I had a bad head gasket on my 97 STS with approx 210K miles. since it had so many miles, I decided to pick up a used engine "cheap" instead of studding the block. The engine is a 97 SLS motor that 'supposedly" has around 100K miles...the seller had a few parts left over from the car...to include an old, but intact radiator (hopefully a good sign). I know I know....fix my other engine...it's a "known quantity"....but I'm fixing the motor so a 16 YO new driver can go 2-3 miles to school every day...so if the quick swap get's another year out of the car, then it's a HUGE win. the engine turned smoothly with a breaker bar...and the plugs looked "ok"....since I HATE grease, the swap includes replacing most of the gaskets...and I needed to swap the intake cams out (to make it an STS again AND since the clown had broken the water pump drive off one of them)....what I found upon removing the front cover has me scratching my head....

This engine had NOT been disassembled recently...WAY too much evenly distributed grease...and the gaskets looked like the GM variety...not the bright blue felpro...but upon trying to put the engine at TDC, the dot on the crank did NOT line up with the upper drive gear.....off by about 45%...and one of the intake cams was off by one tooth....I counted teeth between the marks on both sides....just the one cam was off. As far as I can tell, all of the valves looked pretty good....none appear bent....so I think that one of two things happened....either this motor left the factory F'D up...or a dealer "fixed" a gasket....and made some major mistakes....ie it looks like they put the bottom end at TDC, (or just put the dot pointing up) and tried to align the cams without caring where the intermediate gear was...which I guess is "ok"....just makes me scratch my head...but the one intake came being a tooth off.....

Any idea just how much "accidentally indexing" a cam would have hurt performance?

BTW....the head bolts on the old engine were TIGHT!!!! I only found a couple "wet" / Bad ones...and they seemed tight, but did not have the enormous "pop"...looks like the cylinder closest to the water pump was the culprit!

04-19-11, 04:13 PM
crank and intermediate sprocket dots face each other. crank at 12, inter at 6. than all 4 cam sprockets are at "12" or perpendicular to head surface. at TDC, crank sprocket which is keyed, has to be right. or at 12. you say it is off by 45deg? now, will a mistimed motor cause bent valves? probably. and a broken cam WP extension is cause for concern.

04-19-11, 09:24 PM
I would be real leery of an engine with a broken waterpump shaft, I can't imagine how much force ot took, I would pass on this one.

04-21-11, 11:00 AM
Jim, the claim was he broke it off trying to remove a damaged waterpump drive pully.

I'm about to put the engine back in....wish me luck....

BTW, I haven't seen it mentioned here...but this is the first engine that I've ever seen where the timing marks on the crank an the intermediate sprocket don't line up on every turn....or ever other turn....so the marks qare there for the installation, but if you turn the engine a couple times after putting the tensioners back in....you have to turn it several times before all the marks line up again.

04-21-11, 02:00 PM
You must roll the engine an odd number of revolutions to get them ALL to line up again due to the odd number of teeth on the different sprockets. I believe the GM manual says 17 turns.

The sheer force involved to break off a hardened iron camshaft extension points directly to the use of a hammer, and a big one, to remove the drive pulley hub as opposed to a proper pump hub puller: nice and gentle. Pray that you don't have cam bearing saddle problems on that end of the front intake cam.

04-21-11, 05:34 PM
saddle and lifters looked good....had to swap out the cams anyway...used a generous amount of assembly lube on the lobes and lifters.

Thanks for the info on the number of turns! I guess I didn't read the manual that closely, and it was pretty strange when it didn't line up again after one or two turns!

04-22-11, 02:58 PM
valve covers and timing cover are on so you can't answer this question. if crank is at tdc and cam dots are at 12oclock, than turning crank 360 means all 4 cam dots will be at 6 now? its a 4 cycle motor. 1 crank turn is 1/2 cam turn. 2nd point. turn crank 720 and all cam dots are at 12 again.

04-24-11, 12:27 PM

The cams and crank line up appropriately, however, the marks on the intermediate gear do NOT on every turn.....so the crank will be at twelve, and the cams will be at 12 (or 6) and but the intermediate gear will be at some random angle

04-25-11, 10:11 AM
what is the purpose of the intermediate gear timing dot? you only care that the crank is at tdc and cam dots are at 12. inter gear dot could be pointed anywhere. been told engine must make 7 revs to get timing dots to line up. but back to the main point. crank is at tdc, cam dots are at 12 or 6.