MG MGB and MGB GT Tech Talk
I'm helping a buddy assemble a 5-main engine. He installed the crank and it was pretty hard to turn. All indications are the thrust bearings. Crank and bearings are standard. With the rods and pistons in, it's naturally quite a bit tighter, but can still be turned. Plenty of assembly lube used. Question: will the bearing "settle" during run-in, or is there danger of galling a surface? How tight is too tight?? Thanks.
You certainly have asked a subjective question. Did you mic' everything first?
With only the crank installed it should turn with minor effort, but not spin freely at release. With pistons in, quite a bit more effort is needed and may vary depending on the piston fit and the grit and finish of the bore.
Brad
What is the crank end float? Should turn freely if assembled with oil, a bit harder if you used "grease". Crank will feel a bit tight until caps are torqued and bearings "crushed".
If end float is ok, at least .003" then spin the crank with a drill motor for a minute or two, then check the bearings for shiny spots to see where and why it's tight.
Did you solvent wipe the bearings to remove shipping oil?
If you loosen the center cap and it frees up it is probably the thrust.
If it's rings/bore finish it will turn much harder at piston mid-way travel.
ABSOLUTELY the first thing to do is check that the main bearing caps are in the correct positions and facing the correct way. Hopefully someone number stamped them BEFORE removal. Next: Plastigage the bearing clearances? If the clearances are correct the crank will turn freely. Do one bearing at a time and after determining it is OK remove the plastigage material, retorque the cap and make sure the crank turns OK. Leave it torqued and go to the next bearing and repeat. Do this with the thrust bearings out. You should be able to turn it easily by hand after torquing each bearing. If it still doesn't return to step one. Then put the thrust bearings back in and check for a few thousand's end float or play. Never seen thrust bearings cause the crank to turn hard. I've had folks in the past just remove the bearing caps and throw them in a box without marking them. It took a VERY intense magnifying glass and a lot of time to line up the machining marks on each cap to get them back to the correct positions.
Good luck.
Tom
My vote is for the thrust bearings. I had a new set that bound up the crank & ended up reusing the originals. Don't rely on it "breaking in" . If there isn't enough clearance for oil, it will eat the brgs and crank.
yup...must be the thrust washers....with the crank in and the main caps torqued..it should spin freely. If not, check the end float...then remove the cap and take out the thrust washers. Measure them..it they are too thick replace one side with the new ones (the rear side of the cap, the thrust side) and use the old ones on the front side of the cap. That might do it...if not, use all 4 old ones.
FWIW, every MGB engine I have rebuilt has needed to be line bored to make them feel "right" after assembly. I'd suggest you get someone who knows how to mike the bearing bores before you call it good. Hap is right about the thrust bearings being too thick-just went through that with an engine I'm building now.
Great advice, guys! Since this was a pretty low-mile engine, it just needed cylinders honed, crank polished. We're trying to go on the cheap- but certainly want it to last. I don't know what bearings he got, but there is NO end-play in the crank, which, again points to thrust bearings. I think we'll go with the consensus and start pulling main caps, checking each in turn. Thanks again...will return with more questions, I'm sure.
MY procedure ,,first the plastigage after satisfied ,,i rotate the crank immediately
after each bearing is tourqued ..
dont wait until all torqued ,,and then check ??