High Comp 120cc Build

[8ad-f85]

It would be pretty hard for a automotive hack to argue with a real machinist findings :twocents:

Yeah definitely!
You always offer a great bridge between both perspectives!
My last posts were more to familiarize with the crank grinding process and how things may be done differently depending on machines, and what types of problems slip right on by the customer ill-equipped to check such things.

 

[samIam]

Talked to the machine shop and they said the bolts were torqued to 110 for the line hone which is what I had it at when it had the tight spot. They said to double check that nothing was in the saddles or under the bearings and retry. When I was checking the back of the thrust bearing, I thought I felt something come off but didn't see anything. He also said that I could run some 1500 grit sand paper in the high spot if needed. Gonna mess with the motor again tonight and run some plastigauge to double check what my snap gauges are saying. Also want to do what y'all are saying by spinning the crank with only the outside bearings in to see if there is any runout in the #3 main.

 

[The Mad Cadder]

Make sure the plastigauge isn't out of date ..

Bear in mind it is just going to give you a general idea..

I would try to plastigauge it in the same spot you used the snappers

I hate plastigauge.. it must be done dry..

I would not sand the bearing :no:

BTW
Did you ask them what they torqued it to ?? or did you tell them you that you went 110 first

 

[samIam]

They tried to give me some old broken plasitgauge at first, it was in about 15 pieces in the paper. We went through it all and got the best one. I'll plastigauge all the bearings. I don't think I was gonna sand the bearing, sanding a high spot doesnt find the problem. I can't remember if I said 110 first or not but he said they do everything at the torque listed by the stud manufacture with manufacture recommended lube.

 

[8ad-f85]

Did it still have a tight spot after backing down the torque some?
Any shop rag lint, burrs or high spots behind the shells?
It only takes a little over .001" to find contact, a hair is nearly .003"
Where your caps are ground don't appear deburred.
Solvent and then compressed air should be the last things to touch the parts prior to oil.
Some brands of bearings in the last few years have been needing the backsides cleaned a bit better than normal.
I've found machining chips stuck to the backs from time to time, right in the packaging.
It's OK to very lightly hit the backsides of the bearings with fine stone or paper, but only to true up a high spot, burr or embedded particle.

Might want to measure the main's bores w/o the bearings and look for roundness.
Make sure and check where it corresponds to the contact to the bearings as well.
Caliper the bearing thickness where it makes contact in the front and towards the rear.
I would measure all over the crank and those bores.
If you do use a snap gauge, drag it all around on the same setting.
You're really going to need a dial bore gauge to see better. The inexpensive ones are fine.

Seems odd that you have contact on 4 of the 5 bearings, and only towards the front of each cap, except the front one.
The front one looks like something behind the shell.
You might have to ink them up for another go at it.

If it isn't an assembly problem then it appears there is taper from the hone job, crank grind, or both.
Both can easily happen and can be ongoing problems with either equipment or cutting unfamiliar blocks/cranks.
I'll comment on that IF found.
Is it possible the bearings hung up on a sharp edge left on the cap from the hone?

I'm also curious if they did both operations and if so, what specs they used?
Places dealing with performance know better than to simply "grind to -.010"" and "go nominal" on the bearing bores.
It's quite normal to use either to steer a clearance into the desired spec and should be discussed with the customer.

 

[samIam]

When you say solvent, you talking mineral spirits?

I'll get back to the rest of your post when I get back from the garage, still troubleshooting.

 

[8ad-f85]

Wasn't being specific. The emphasis is on getting the parts lint and grit free for assembly.
I liked Frankeregal's tip on nylons wiping the crank, as long as air touches it last.

 

[Member 3508]

If you have to do anything to the babbitt of the bearings, use a synthetic steel wool, like the 3M scuff pads. They remove material pretty slowly so you can sneak up on it.

Grit on the babbitts makes me nervous. That stuff is like clay bar. Once stuff gets into it, you're not likely to get it out.

 

[samIam]

So I used the plastigauge last night. They were a little more then .002 at all but the rear which was close to .003, maybe .0028-ish.

Also put it back together wet again and tried turning it at different torque values. The problem is this time I used a different assembly lube and can't turn the crank at all under human power at 110lbs, even after breakaway using a pry bar. I can turn it at 90 and 70. When turning it at 70 and 90lbs, it still has the the tight. Then I loosened up the thrust bearing and it turns smooth as butter, no tight spots.

Gotta go buy some nylons and some scuff pads. Babbitt of the bearings means the back, right?

Thanks again for all the help y'all. Not many forums would spend two pages with a guy trying to install a crank.

The Joe Gibbs stuff was a lot easier to turn then the Permatex.

 

[8ad-f85]

Before you start scuffing your bearing, there's quite a few unanswered Q's.
Did the contact with the other bearings go away?
Can you orient the crank in the bind position and plastigage it, then again 180*, to see if the crank is off vs. the main line?
I think for diagnostic purposes, it might be simpler to ink up the previously contacted bearings with sharpie and use plain engine oil rather than final assembly lube.
Maybe put the top ones on dry until you get through this.
Even though there's been known issues with thrust bearings I wouldn't assume the main line alignment or crank grind are acceptable yet.

I seem to recall reading that some thrust bearings have too much crush or an interference with the flange portion that shows up under torque, locking the crank. (did Dave B. have this?)
The witness marks from contact still indicate that there may be issues with tapered machining, and that would be unacceptable.
I would not proceed with assembly until you can figure that out.

A shop near me was found to have been grinding cranks for years with the machine's chucks "off" of each other by .015", causing the cranks' mains to be out of alignment, by a few thou per journal...
It's also not unheard of to have to turn the block around during the line hone process to combat taper, esp. with makes they don't do many of. There's a learning curve for some makes and shops don't always like to take that kind of time to do this.

 

[The Mad Cadder]

That looks like less then .002

Something aint right!! If they machines it properly at 110 ft lbs
it wouldn't get thighter adding torque over 80 if anything should
make it looser..

At less it dosent have the same distortion to it as when it was
( supposedly ) honed.. I bet the hone was not cylindrical and
sagging at the rear main thus it is bigger !! So the bores are not
true

You should not have those issues and sanding
the bearing babbitt to make it work is a no go..
I

When i use plastigauge I put it at several locations on same journal
This gives a better idea of where the crank sits..

What does the shop have to say about your finding ??

 

[8ad-f85]

I'm also trying to think of what would change drastically from assembling one time and having a tight spot VS. a second time and locking the crank up tight.
The threads burnishing from a few more torque cycles increases the clamping force over when first done, but as Mad suggests...there's a serious problem!
Assembly lubes that are thick are intended for engines that sit a while or maybe don't get oil flow right away.
I don't use them, just motor oil. There shouldn't be much difference in break away torque, other than what you detect being able to turn the crank with your hand on the snout.

Please re read procedure on "setting" the thrust bearing cap during assembly.

 

[The Mad Cadder]

Did you check end play ??
That may be your trust bearing issue

I highly suspect they @$!#/ up your line hone.. this is kinda why Iam
leaning toward line bore.. Stones in the hone wear .. hones hanging 2 or 3
feet away from their mount make oval sagging bores.

8 suggested some flip the block 180* and hone from both ends.. this may be
a solution for you..at the same time have the other 4 opened to the same size
a the rear

I would take it back and make them check it in front of you

 

[Member 3508]

I meant to say the surface where the crank rides when i said babbitt.

For not being able to turn the crank, its pretty cold outside so the lube is going to be THICK, it probably doesnt want to flow. Not sure where you're doing your assembly, but if its like me, it was in a cold garage.

I had the same thing happen to me, it freaked me out. So i got some 0weight oil, heated it up in a pan where it felt warm to the touch, and tried it again. I also put a space heater on the block, and brought the crank indoors for a couple of hours to try and get everything to a summer-like temperature. Be careful if you bring the crank inside, spray some WD40 on the journals. Cold Crank + Warm Air = Condensation.

Tried it again, and i was able to get 3 or 4 revolutions out of the crank now if i gave it a spin with my hand once.

 

[samIam]

Talked to the machine shop and he will be stopping by this afternoon.

 

[one finger john]

That's something you hardly see is a machine shop owner coming to the customers home to see what the potential problem is. Like doctors making house calls. A rarity in this day & age.

John

 

[samIam]

It's pretty awesome. Two brothers that used to run a red rooster machine shop before it closed. This is motor 6 through them. All started with a small block Chevy...

He's on his way now, ill let you know what he says.

 

[dave brode]

The babbit layer on trimetal bearings is VERY thin, less than .001", I bet. I would be leery of any shop that recommended sanding the bearing surface that rides on the journals. :yikes:

You can try setting the thrust brg, but I bet that will have to sand it. I'm talking the flange. I like bimetal alum for cast cranks, but removing the babbit layer on the flange area is not an issue. Rub the flange on fine paper taped to glass.

Dave

 

[dave brode]

Fwiw;

I would take time to place plastic-gauge at 10 and 2 [call it 4 and 8 if you prefer] on all 5, all at the same time. IMO, it should not show tighter on one side than the other.

 

[samIam]

So.....caps on backwards! I thought the tabs were to go on opposite sides, they don't. Turns smooth now at 110lbs. I'll bet the clearances will match the rear cap that was on correctly and had .003" but haven't checked yet. He measured end play and saw it was too tight with the cap on but good with out it. Gonna get that where it should and check some other stuff that yall mentioned before I consider it good.

I'll also reply more in dept to your replies when I get to a computer, my phone doesn't like this forum as much as I do.