Blooze Own: An F355 Six Speed N* Build Thread (Page 3/126) darkhorizon APR 27, 04:34 PM Northstar rebuild.... YIKES! Bloozberry APR 27, 05:21 PM I finally found the pictures of the cam lobes and followers in my digital "shoebox". First though, here’s a close up of the hot oil varnished cams. It’s hard to see anything problematic from this photo, although you’ll notice here how several cam-bearing cap bolts have been removed because I got curious after finding one of them loose! Now I doubt this is a common problem with Northstars, because I would’ve probably read about it given the volumes of info I researched before diving into this, but it is something you should check if planning on using a warmed-over Caddy engine. The one cap bolt was loose because it was broken(!) where the threaded portion met the shank, its weakest point. From the fracture site, the failure mode was obviously tensile loading and not shear, in other words, it broke after it was torqued and not during the tightening of the bolt. I'm guessing that someone didn’t have the torque specs for the bolts or didn’t use a torque wrench to tighten the caps at some point in the engine’s history. In any case, this one was torqued beyond the bolt’s yield point but not quite enough to break it. The loading of the bearing caps from operating forces on the cam were enough to tip the scales on it and break it in tension. Now have a look at the picture. The bolt on the left is an unused one, the one on the right is the broken one (duh), and the one in the middle is what four other cam-bearing cap bolts looked like on that head after I removed them. See anything a little off? The eagle-eyed among you will notice the “necking” or narrowing of the bolt diameter where the threads meet the shank… exactly where the other one broke. Someone clearly used the “it feels tight enough” approach on these caps. I couldn’t be certain of the condition of the remaining bolts, so I turfed them all. Here’s the picture of the exhaust cam lobe I promised earlier. All the lobes on both exhaust cams were like this. Clearly worn beyond reuse without reconditioning or replacement. And here’s what worn cam lobes do to cam followers. The one in the background is from an intake cam so it’s better, but at this stage there was no point in keeping any of the followers. And here’s what the exhaust valves looked like. Beyond grinding. Kaput. Cha-ching! More cash register sounds at my machine shop. By the way, this was supposed to be the low mileage engine. When I removed the valve covers off the high mileage engine, they looked about the same for wear and tear. But that’s OK because I probably would’ve replaced most of this stuff on spec anyways. No point in rebuilding an engine if you’re just going to throw the old parts back in it. pmbrunelle APR 27, 05:29 PM That's really a lot of cha-ching! Cha-ching times 32 valves and times 4 cams. Does the other engine have useable cams, tappets, valves? Did you disassemble that one? Bloozberry APR 27, 05:39 PM I didn't disassemble the heads on the other engine to the same degree, but I knew that engine had 250K kms on it. Even if it looked better after taking it apart, I would've replaced the moving parts anyways. 250K kms is just too much to just transplant into a car and hope for the best. White Spyder APR 27, 08:17 PM One day....one day......when I hit the lottery.......... Fiero Owner APR 27, 08:51 PM Very interesting. Will be keeping an eye on this. Nice to see a project like this close to home too. dratts APR 27, 08:52 PM My first thought was look around for another set of heads. Then I thought "I wonder what the rest of the engine is like." I hope it doesn't turn into a huge build and lots of dollars. I agree, I would pull any engine apart to check the cams valves bearings and crank, and to install time serts, but at the point you are I think it might be cheaper to source a good engine over a rebuild. Just an opinion. From what some of the storys I've heard you can throw money at these engines just like they're boats. Bloozberry APR 27, 08:54 PM Hey! Hantsport! Right on. Never noticed you were so close there Fiero Owner. Bloozberry APR 27, 09:48 PM quote Originally posted by dratts: I hope it doesn't turn into a huge build and lots of dollars. Thanks for your advice dratts... but I think if you want a reliable Northstar in the long term, there's no cheap way to do it. You either spend your money up front and buy a late model engine (and try to figure out the cam phasing), or buy a cheap early engine and spend your money rebuilding it. You have to expect (as I did) that a 10 to 15 year old engine is going to be worn close to the end of it's useful first life. One way or the other, you really really have to want one to be able to justify a N* financially because there are several engines out there that are cheaper and more powerful. Realistically, I think you have to set aside $5000-$6000 for this engine, in Canada anyways. More if you haven't got the space, time, skills or tools to do it yourself. dratts APR 27, 11:51 PM Well I shouldn't be giving "advice". If your posts didn't convince me that you probably know a lot more than me, your shop would. Still I remember when cadillac dealers didn't fix these engines, they just replaced them. There was a time when you could get a brand new N* for $2500 from an outfit I think was called speedway motors or something like that, but that was a while back. Anyway have fun it's gonna be a great engine.