90 engine rebuild

johnny928 · Post by **johnny928** » Tue Jan 03, 2006 6:12 pm

I am in the middle of an engine rebuild right now. I had the block and crank speced at a machine shop. I installed the new main bearings and put the main caps on. Everything has been pre lubed as well. When turning the crank by hand it turns smoothly but once I stop turning it and try to turn it again it takes a good push to get it to start turning again. Is that normal??

bscutt · Post by **bscutt** » Tue Jan 03, 2006 6:49 pm

I would say yes that's probably normal. I've never rebuilt a VW diesel engine but have rebuilt plenty of engines from 1959 Jeep 4 cylinder up to big block Pontiacs, including my 1941 Chevy motor. If at all in doubt, loosen each main cap bolt a quarter turn and go back through the torque sequence with a good calibrated torque wrench. You can also go get plastigages of the appropropriate clearance specs and double check the tolerance with those. I've never used them but I'm sure someone on here has. You should be able to rotate it with some resistance but not have to use a wrench (assuming you have a pulley or flywheel to turn)

sideburns · Post by **sideburns** » Tue Jan 03, 2006 8:20 pm

Turn the engine with a ratchet on the crank pully, turn it around 2 complete turns (CW) and feel for the compression, and after it goes past compression it will turn very easily, then get hard again, as another cylinder comes up on compression. i would say that is likely what you encountered, if it is not this, then i would check the mains and rod cap bearing clearances, as described above, make sure not to turn the crank while your plastiguage is in there or it will ruin your results. make sure all of your bearing caps were replaced in the correct orientation as they came off, if even one is put on the wrong way, it could result in problems

VW cat · Post by **VW cat** » Tue Jan 03, 2006 8:51 pm

Without pistons, a crankshaft once turning should continue to turn for a short distance on it's own when you let go of it; unless it's cold in your garage and you have some very thick grease on the bearings. It pays to buy the engine assembly grease, I think. If the crank stops the instant you let go, you may have an alignment problem or your thrust bearing is not properly seated. Removing the new bearings and looking at the surface, show if there is a high spot. They have a soft coating when new. If it's an align-bore problem, it's sometimes caused by a previous spun main bearing. I think it's good advice above to pull one cap off and it's bearing, at a time, and see if it makes a difference. If in doubt a machine shop foreman would quickly check it for you. As noted above the caps have to be on the right way in the right spot.

johnny928 · Post by **johnny928** » Wed Jan 04, 2006 1:22 pm

Thanks for the replys. I don't have the pistons in there yet. I seated the bearings in there and put white grease and oil on the bearings. I put the crank in there and attached the bearing caps. I can turn it by hand smoothly but if I try to give it a spin it dosen't spin freely. Is it because of the grease?? I took the caps off to inspect the bearings again and there is one spot on one of the bearings like were it looks like a bit of wear but I don't know if that is normal. When I am spining it by hand it doesn't bind or anything. It is just a little sticky when trying to spin it the first time from a stand still. Any other ideas? I got the block and crank checked at a machine shop and they said everything was ok spec wise and I put brand new bearings in. Bearing #3 came with the shoulder attached to it and it meets the spec for lateral movment of the crank.

VW cat · Post by **VW cat** » Wed Jan 04, 2006 7:09 pm

I don't think you have anything to worry about. If your old bearings looked fine, your laughing. Let us know how she runs.

johnny928 · Post by **johnny928** » Thu Jan 05, 2006 10:35 am

Thanks for the help guys. The old bearings looked fine so I will just install the new bearings and then put her together. I will put the pistons in tonight. Quick question about the pistons, The block was honed and it checked out ok. Once the pistons are in how easy should they be to be moved up and down when not attached to the crank?

libbybapa · Post by **libbybapa** » Thu Jan 05, 2006 1:38 pm

They are not very easy to move up and down due to the friction of the rings against the freshly honed cylinders.

Andrew

johnny928 · Post by **johnny928** » Thu Jan 05, 2006 1:42 pm

Thanks for the info. I will post back here once I have made some more progress.

sideburns · Post by **sideburns** » Thu Jan 05, 2006 5:18 pm

just as a note, dont use synthetic oil when breaking in your engine, it isnt sticky enough and your rings wont seat properly.

johnny928 · Post by **johnny928** » Fri Jan 06, 2006 10:46 am

Ok so I found the problem. I ended up trying another crank and i got the same results. The bearings in #2,3,4,5 all looked good but the bearing in the cap of #1 had a bit of wear from turning the crank manually. The wear amount was the width of the bearing and about 1 cm up from the end. So it looks like it is a little tight there. My question is, should I get that looked into or should it be ok if I ran it like that? I know it isn't the crank because I got the same result from 2 cranks that were both checked at a machine shop. The bearings are new so it is most likely something with the block being a little out.

libbybapa · Post by **libbybapa** » Fri Jan 06, 2006 2:54 pm

You should remove the bearings from the cap and saddle. Make sure that there is nothing (piece of dirt) between the bearing and the cap/saddle). Try turning the crank with just that bearing removed, but all others in place. There should not be a significant difference in turning force required with just one bearing removed. There should be an oil clearance betwen the crank and bearing. If there is not, you very well might have a problem. I would recommend getting plastigage and checking the oil clearances of each and making sure they are all within spec. You could also try placing that bearing in another saddle and seeing if the problem moves with the bearing. If it does, then get the set replaced. I have twice received stes of VW bearings that had one bearing of the wrong size in the set. Is the crank ground? Case align bored? If it was and the problem persists at the same bearing location, despite moving the bearing to another location, then use plastigage for sure, and then get the machine shop to do it right this time. Doublecheck their work afterwards considering they didn't get it right the first time.

Andrew

johnny928 · Post by **johnny928** » Fri Jan 06, 2006 3:12 pm

I will try removing the bearing and moving it around to different spots tonight. I just have a bad feeling that there is something outta whack. I might have to take it back to the machine shop to get it rechecked. I just thought that if they checked the block and the pistons and the crankand they said that everything was ok that I wouldn't run into anything like this. Oh well, I will post results after moving the bearings around

libbybapa · Post by **libbybapa** » Fri Jan 06, 2006 6:19 pm

I guess in an ideal world...

Triple check, quadruple check. Plastigage is available at the counter of any auto parts store for very cheap. Be sure you know what the clearance is that you will be check as it comes in various color coded sizes. I'm pretty sure you need the red, but it's been several months since I did crank and rods of a vw diesel. It is a thin "wire" of very accurately sized squishable plastic. You place a small section between the shaft and the bearing and then crank the cap down without rotating the bearing. The plastigage will squish. You then remove the cap and measure the width of the squished plastic using the gauge printed on the packaging. It is a very easy and inexpensive way that you can very accurately measure the clearance between parts and check to see if it is in spec for new parts. Even the Best machine shop makes mistakes that they don't catch, and very, very few are the best... I would highly recommend using plastigage on rods and crank prior to any engine assembly especially if you get parts machined. Even if just swapping bearings it is a good idea, as you can catch the errant bad new bearing. As I previously mentioned I have caught a couple.

As far as your specific dilema. If a bearing is "tight" then it is obviously one of four things. Either the crank journal is large, the saddle/cap circle is too small, the bearing is too fat or there is crud somewhere causing the interference. Regardless you want to get it right. Good luck.

Andrew

Post by **Fatmobile** » Sat Jan 07, 2006 2:07 am

The plastigauge will stick to the bearings after it is squished. Don't scrap it off. Use carb cleaner or brake cleaner because it is petro soluable.
I sometimes have a hard time getting it to stay in place so I stick it there with a little silicone dielectric compound ... non-petro grease.
Yeah, no matter what the shop says, plastigauge it as you put it together.