Hi , its my first time on here and could figure out a search in the forums so hopefully this hasn't been covered. I am rebuilding an aaz out of a mk3 jetta to put into a 1988 cabrio, I just replace the crankshaft bearings and when I torque them to the specs I found ( 48ft/lbs) the crank no longer free spins. everything was lubed with clean diesel oil and I torqued in a star pattern and gradually starting at 20, 35 then 48. At 48 it still turns freely although fairly stiff but the reference I am using says 48 plus 90 degrees and that makes it completely seize. Thanks for the help, this is my first engine rebuild, im an aircraft mechanic by trade in the RCAF but this is a whole other beast.
Are they the correct bearings? Did you get oversize by mistake? Any chance you've made a mistake on which cap goes in which location or flipped one or more around the wrong way? I would pull the crank and look for marks on the bearings to see where it is binding. You could plastigage the crank and bearings or pull the crank, install the caps with bearings, then use bore gauge and mics to see what the crank clearance actually is.
There are two types of AAZ main bearing bolts. The set that is threaded the whole length of the bolt are Torque-To-Yield (TTY) and should ALWAYS be replaced if they are ever loosened after being torqued. The bolts that are not threaded the entire length of the shaft are not TTY and can be reused. Main studs are a good idea in either case. I would *not* recommend reusing the AAZ TTY main bolts. They are known to fail when reused.
I removed the crank and made sure that all the bearings were set the right way etc. The bearings arent or shouldnt be oversized ( its not specified and the website is normally good at posting it) My bolts are threaded all the way so ill order more. I double verified everythign was installed correctly and still the same story, at 48 ft lbs I can still move the crank by hand but when I add that 1/4 turn it becomes too hard to move, tomorrow I may try with a wrench too see just how hard it is but I am concerned. Ill check my local stores for new bolts as german parts.ca isnt showing any.. After seeing the condition of the old ones I should have just left them alone but I figured while im there..
Ok, bearings were set the right way. Were the caps placed in the correct locations and are the caps flipped the right way?
The website you got the bearings from doesn't say whether or not they are oversize? What brand are the bearings? Where did you get them. An incorrect bearing happens every so often even with the best suppliers. In the last 15 years or so I have come across TWO incorrect bearings in sealed sets of high quality German-made bearings where all of the other bearings were correct, so it does happen. I wouldn't work too hard with a wrench and I'd measure instead.
Those main bolts are not readily available. Last time I got a set I got them from IDParts. Do all of your testing with the current bolts until you know everything is right and then install the new bolts for the final tightening.
Flip the bearings over and wipe them with a clean rag. You will likely see where they are pinching the crank. If there are not any visible marks, then as I mentioned before, you can use plastigage to over each of the journals and it will probably be obvious which one(s) is(are) too tight. Alternatively, as I mentioned before, you could pull the crank, remount the caps/bearings and use a bore gauge and mic to find the clearance on each. The bore gauge would likely tell you what was the issue.
Changing the main bearings 'because you're in there' is not usually at all beneficial and is usually, if anything, detrimental. The main bearings on these engines are usually within spec for new parts even after hundreds of thousands of miles (e.g. 200,000+ miles) unless oil changes were neglected. If they are within spec for new parts there is no benefit to changing them and you run the risk of actually causing additional wear to the crank when wearing in the new bearings.
If you still have the original bearings and have kept them in order for their locations, then I would replace them and plastigage them. If the clearance is within spec for new parts then reinstall the caps with the new bolts torqued to spec and consider it a learning experience.
sounds like a plan, ill get the plastigage, ive always wanted to try that. Ill chuck that to inexperience and hopefully the wasted 60$ ( 80 once ive bought new bolts ) serves as a reminder. I have the old ones but no longer paired or in order, ill use the plastigage on all caps and if the tolerance on one so too tight ill replace it with the one with the largest gap to see if I cant get it to fit. I definitely figured while I was that deep and spending 1000$ rebuilding that the extra 60$ bearings made sense, should have listened to the old "if it aint broke dont fix it" motto. Thanks for all the help. While were at it would you replace the rod end bearings then?
