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Rod Big End clearance problem??????

Posted By: DemonDust

Rod Big End clearance problem?????? - 08/16/09 09:32 PM

I got cylinders 1 and 2 in my block. On the radius side of the crank I have .020+ But I can't get a measurement between the rods. Why is this? The rods should be able to move over as there is clearance on both sides of the pin end.
Posted By: PC-CHARGER

Re: Rod Big End clearance problem?????? - 08/16/09 09:36 PM

If you have a radius ground crank instead of a factory one that has an undercut, you will need bearings that have a chamfer on them to clear the crank radius. The rods also have a chamfer on one side that goes to the crank radius as well.
Posted By: DemonDust

Re: Rod Big End clearance problem?????? - 08/16/09 09:49 PM

Yeah, the chamfers are out toward the radius.
Posted By: PC-CHARGER

Re: Rod Big End clearance problem?????? - 08/16/09 09:59 PM

Sounds like the radius is too large for the amount of chamfer on the bearings. The bearings are riding on the chamfer which pushes the rods together and giving you the exact problem you are seeing. There will be a clearance at the radius side of the rod but they are forced together and no clearance between them. Here's a crude drawing that shows what's going on.
Either you have to have the radius reduced by re-grinding or the bearings will have to be scraped to fit.

Attached picture 5421355-brg.jpg
Posted By: DemonDust

Re: Rod Big End clearance problem?????? - 08/16/09 10:12 PM

I Remeasured everything. My journals are 1.8270 wide. My rods are .8900 wide.

The bearings are narrower than the rod. I'll try to get some pics.

Give me a few mins
Posted By: DemonDust

Re: Rod Big End clearance problem?????? - 08/16/09 10:24 PM

Sorry for the poor pic quality.


Posted By: DemonDust

Re: Rod Big End clearance problem?????? - 08/16/09 10:30 PM

With the caps off everything fits perfect, the rod will sit tight against the journal no problem. Maybe there is only .001-.002 clearance between my rods. I need to get a new feeler gauge, mine only goes down to .004

I'm thinking I may have to machine a little off the unchamfered side of the rod?
Posted By: PC-CHARGER

Re: Rod Big End clearance problem?????? - 08/16/09 10:32 PM

The bearings are narrower than the rod as you have noted but it still appears the edge of the bearing is riding on the lower part of the crank radius. I would bet this is your problem and you may have to scrape the bearings slightly to make them work.
Posted By: galen

Re: Rod Big End clearance problem?????? - 08/16/09 10:33 PM

Looks like edge of bearing is on the radius, if I am seeing pic correctly You will probably see a shiny spot on edge of the bearing where it is riding. You can buy a narrow bearing shell clearanced for this or chamfer them yourself.
Posted By: DemonDust

Re: Rod Big End clearance problem?????? - 08/16/09 10:39 PM

What is the best way to narrow the bearings?
Posted By: PC-CHARGER

Re: Rod Big End clearance problem?????? - 08/16/09 10:47 PM

Your picture is pretty tough to see but it looks like there is very little that needs to be removed. The proper tool is a bearing scraper like this:

http://www.etoolcart.com/bearingscraper.aspx

But if you go slow and easy, a good sharp knife and some patience will work.
Posted By: MR_P_BODY

Re: Rod Big End clearance problem?????? - 08/16/09 10:47 PM

Quote:

What is the best way to narrow the bearings?



I've cut them with a knife to increase the chamfer
Posted By: DemonDust

Re: Rod Big End clearance problem?????? - 08/16/09 10:51 PM

Would a utility knife with a new blade do the trick?
Posted By: PC-CHARGER

Re: Rod Big End clearance problem?????? - 08/16/09 11:05 PM

Done carefully it will likely work. You just need to put a slight chamfer on the edge of the shell so that it clears the radius. Don't try to narrow the whole bearing.
Posted By: MR_P_BODY

Re: Rod Big End clearance problem?????? - 08/16/09 11:08 PM

Quote:

Would a utility knife with a new blade do the trick?



Yes... just light pressure.... your just scrapping it,
it scraps easy
Posted By: lowell66dart

Re: Rod Big End clearance problem?????? - 08/16/09 11:28 PM

Maybe practice with an old bearing first.
Posted By: dodgefarmer

Re: Rod Big End clearance problem?????? - 08/16/09 11:36 PM

Check to see if your bearings are marked upper and lower.

Randy
Posted By: PC-CHARGER

Re: Rod Big End clearance problem?????? - 08/17/09 12:16 AM

The measurements you gave for rod width and the width of the journal equates to.047 rod side clearance for that journal and pair of rods. Once you have the bearings scraped and you actually measure the side clearance, it will be .047. Anything less and the bearings likely need to be scraped a bit more. If you use this method to check the remaing throws, don't assume the same rod width and journal width. Measure them individually.
Posted By: Anonymous

Re: Rod Big End clearance problem?????? - 08/17/09 12:18 AM

Quote:

Check to see if your bearings are marked upper and lower.

Randy



same thing i was thinking. might have one or both in the wrong place.
Posted By: thecarfarmer

Re: Rod Big End clearance problem?????? - 08/17/09 01:02 AM

You might want to throw a mic on the crank to make sure there's no taper on the journals. I had one that 'greew' .0015 (yes, one and a helf thousandths) from the oil hole to where the radius started.

Just something to look out for.

-Bill
Posted By: DemonDust

Re: Rod Big End clearance problem?????? - 08/17/09 01:37 AM

Yeah I checked for upper and lower one of the first things I thought of. I shaved the edge off the bearing and gained tons of clearance by taking a very tiny bit off. Thanks guys for the tips. I've never had this happen before, then again I've never built an engine like this before...

Thanks for all your input..
Posted By: MR_P_BODY

Re: Rod Big End clearance problem?????? - 08/17/09 01:41 AM

Quote:

Yeah I checked for upper and lower one of the first things I thought of. I shaved the edge off the bearing and gained tons of clearance by taking a very tiny bit off. Thanks guys for the tips. I've never had this happen before, then again I've never built an engine like this before...

Thanks for all your input..



Does the rod touch the crank now (side)
Posted By: DemonDust

Re: Rod Big End clearance problem?????? - 08/17/09 03:38 AM

If I push them over and hold them I still have about .013 clearance. Keep in mind before I couldn't even move them a .001. They seem to want to go back to the middle when I rotate the engine. The journals are square. Do I need to take more off the bearing?
Posted By: MR_P_BODY

Re: Rod Big End clearance problem?????? - 08/17/09 04:10 AM

Quote:

If I push them over and hold them I still have about .013 clearance. Keep in mind before I couldn't even move them a .001. They seem to want to go back to the middle when I rotate the engine. The journals are square. Do I need to take more off the bearing?



Yep
Posted By: DemonDust

Re: Rod Big End clearance problem?????? - 08/17/09 04:16 AM

Ok, I'll get to it first thing in the morning. I'll let you know how it goes. Do they keep going back to center because there isn't enough chamfer on the bearing?
Posted By: MR_P_BODY

Re: Rod Big End clearance problem?????? - 08/17/09 04:26 AM

Quote:

Ok, I'll get to it first thing in the morning. I'll let you know how it goes. Do they keep going back to center because there isn't enough chamfer on the bearing?



Hard to say but you shouldnt have to push on them,
should slide to the wall of the crank
Posted By: DemonDust

Re: Rod Big End clearance problem?????? - 08/17/09 02:36 PM

I made a call down to South Carolina this morning and had sent a few emails to the nascar engine shops I'm in contact with. They told me the same thing to chamfer the bearings. When I told one of them I was scraping the bearing he laughed and said are you crazy???? Use a dremel with a small metal bit. You'll be scraping forever to get enough clearance. Another said they use their lathes to turn them down. Not sure how that works.

But anyway I got my air dremel tool out and put my small metal bit in I use for porting and lightly went over the bearing edge. It does a much smoother job than scraping and it turned out very well. Almost looks machined.

Thanks Mr. P for all the tech help, it's greatly appreciated

Now when I rotate the assembly all the rods go to the radius instead of the center of the crank. I have .040+ clearance between the rods now.
Posted By: DemonDust

Re: Rod Big End clearance problem?????? - 08/17/09 02:37 PM

I forgot to say, they go tight up against the radius side of the crank now.
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