crank resistance

[427scr]

Originally Posted by Stu J

During building the rv8 up from scratch today I put in the main bearings, then the crank and then started the con rods with new rings on the pistons too.

After putting in all the pistons and tightening all caps to spec torque I couldn't help but think the crank was a little hard to turn. The front pulley was put on temp just to help but it showed some tight resistance with that... is this normal?
I removed all the pistons just to see if there was any dirt etc but all seemed normal, the crank and big ends are all standard size and oiled accordingly.

I am aware resistance should be there, but this much? without heads on too.

The only real answer is to remove the crank, thoroughly clean it and using a quality micrometer, check the journal sizes to make sure that they are in tolerance.

I speak from bitter experience, having once rebuilt a 1275 mini engine that the engineering company machined the journals too big for the bearings by a few thou. The engine wouldn't turn over by hand and being 16, and being stupid, I thought that was normal. The car wouldn't start on the starter and we should have suspected somthing then. We ended up tow starting it and it lasted 300 miles before it blew up!!!!!!!!!!!! You have been warned.

[Paul B]

There is a difference between firm and solid. When I rebuilt mine this winter I found that one bearing caps "nipped"up when torqued down. On inspection you could see rough marks on the underside of the cap where the bolt goes through and was told this is a result of the torque being released during the normal running of the engine prior to being stripped down, and the cap moves very slightly giving fretting marks.

With careful tapping with a rubber mallet and gentle increases in the torque on the bolts, I was able to get to the final specified torque value without it nipping up. HOWEVER, once all the mains were tightened, I found that the crankshaft needed quite a lot of force to get it turning and much less to keep it moving.

Unless everything is brand new, you will have small compromises such as the bearing cap but I am confident that it will be ok.

As I said, if it is solid, then stop, if firm then you will have to use your judgement.

HTH

Paul

[Stu J]

Now the engine is in and running after the rebuild here is a "before and after" look, I am quite pleased with the results.

[adricar2]

STU
just a thought,
are the bearings Clevite?
anyway check them all i have know an oversize bearing be supplied wrongly in a bearing set. You can measure each one to check if the stampings on the shells are correct.

[tonym]

Looking good Stu, try and keep an eye on your inlet ducting as I've known it collapse at high revs due to the suction

[mylesdw]

In the very wonderful David Vizard book about rebuilding the SBC he gives actual torque figures to expect for turning the crank when installed and then after each pair of pistons are installed. I can't see why it would be much different for an RV8.

[Stu J]

Thanks for the late replies, I should have continued the conclusion in the post when all was sorted instead of posting completed pics.

When I stripped the crank back down to itself it rotated freely so the fault lay with the con rods, each individually placed with all recommended torque settings and gaps/side play calculated.

It had not changed and was still in my opinion too tight, so I moved a couple of endcaps for tight sideways movement and swapped them over to see if it made any difference. This WAS the cause of the stiff rotate, I must have accidently put them in the wrong order on removal, or it was them bl**dy gremlins....

[wilf]

So pleased you stopped to double check and rectify at this stage! Is what good engine building is all about.