Loose Rod
 

I am re assembling an engine that has been rebuilt and I have a problem. After applying 50 pounds of torque, the rod is still loose on the crankshaft. This is with new rods and insert bearings. No shims. Was the crankshaft ground too far?

Re: Loose Rod
 

If you don't have measuring tools Use aluminum foil--- figure how many layers lock it up--try the rod and bearing on a different journal see if it fits different -

Guess I should have asked which way it is "loose", it should move side to side a little--- but if it rattles around in every direction--- and check the bearing inserts for the size or other numbers and look at the others to see if the same

Re: Loose Rod
 

Whats the clearance ? Thats a must know.

Re: Loose Rod
 

I was having too much rotational play on the crankshaft. I took the rod off of #1 and switched it with #4, and now it fits better on that one. But I tried the rest of them out and they have the opposite problem of being too tight. Guess I have to get shims now for the other three?

Re: Loose Rod
 

Why are you into this block? What is the rebuilders opinion? Is not 50# on the rod nuts a bit much?

Re: Loose Rod
 

Why would you have shims with inserted bearings??


Bob

Re: Loose Rod
 

I should not have said rebuilt. I had the block machined and parts purchased. Reccommended torque on the rods is 45 pounds.

How else can I loosen a rod up?

Re: Loose Rod
 

You have a problem there. Insert bearings are available in standard and plus sizes to fit known crankshaft crank pin journal diameters. The crank pin journals need to be measured with a micrometer to see if they are close to some standard or oversize diameter. The bearings inserts should be of a known inside diameter and fit snug to the con rod big end with the locking tabs in their respective grooves. Plastigauge can be used to check clearances. Bearing shells should be marked for part number and size on the back of each shell. Check all this yourself or contact the shop that did the work for help.

The crankshaft may need some time in a crank grinding machine if the sizes don't match up. Only a poured babbitt block & connecting rods need shims.

Re: Loose Rod
 

When they machined the block did they have the parts to gauge?

Re: Loose Rod
 

Yes they had all of the parts. They are a pretty reputable shop around here, they know Model A's. Which is why it is odd to me. So my inserts for the rods might be too large?

Re: Loose Rod
 

Hydrodynamic principal is .001 clearance for each inch of shaft diameter..on a model a engine the correct oil clearance is .0015,regardless of the bearing used,insert or poured.Fit your connecting rods to this standard.Shortcuts are not the formula for bearing life.

Re: Loose Rod
 

If a crankshaft has been ground, the journals and therefore the bearings will be undersize. This is the opposite to the bores which end up larger after a rebore and therefore, pitons would be oversize.
This is a common and puzzling error made in parts catalogues and repair manuals that I have seen.

Re: Loose Rod
 

I have assembled upwards of 180 engines with inserted rods supplied by Antique Engine Rebuilding (AER) and of those, I have run about 100 of them on an engine dyno to break them in. What I have learned from this work is that rod clearances need to be between .0015" and .0018" based on the methods I use to check assembly clearances. Much over .0018" and a slight rod knock may start after 2 hours of running/break-in. With over .002" clearance it is most likely to develop a knock during the break-in. I have not tried less than .0015" during assembly and at that clearance, I have not had a bearing failure due to lack of oil clearance at a rod bearing.

The suggested final rod bolt torque is 35# for AER and Snyder's insert bearing rods. If torquing to 45# there is a risk of twisting/distorting the rod cap. This twisted condition may also cause a rod knock.

When checking rod journal diameter during assembly, I find that a mid-range journal size within the rod and bearing manufacturer's stated spec. provides the clearances I am looking for.

For loosening the fit on the tight rods, I suggest taking the crankshaft to a crankshaft grinder and have them polish the journals until you obtain the proper fit. Most shops will have a motor driven abrasive belt polisher to complete this adjustment. I have had this process done a couple times prior to purchasing equipment for my Sunnen precision pin hone to adjust the fit. I hope it all works out well for you.
Good Day!

Re: Loose Rod
 

https://i.imgur.com/fzfsoKQ.jpg?1

Hydrodynamic lubrication is used on all types of machinery,its the basis for lubricating internal combustion engine shafts,pressurized or gravity system,insert or poured bearings,high or low compression just about every engine runs on a thin film of oil. Whats interesting to me is its a standard measurement,.001 clearance per inch of shaft diameter..run a 10 inch crankshaft journal? its hydrodynamically supported by .010 film of oil.This is where folks get confused with journals and bearing sizes and all kinds of hoohah about engine oil...get .0015 with a model a rod and it will live a long life,use an engine oil with high load and shear characteristics to protect the film.Diesel grade engine oils have these additives.

If the bore is cut correctly and the crankshaft and bearings are fit to .0015 on your rods you are golden.If you can shim your insert bearings to achieve .0015 youre golden...yep,the golden rule doesnt change..fire your machinist? maybe but you can make a tight insert work with fitted shims

Re: Loose Rod
 

Chris,
One problem I have had with inserts are interference with the radius ground on the crank journal. It is pretty easy to identify when you are looking for it.
If this is the case, a bearing scraper can be used to relieve the edge where it is riding on the radius.

It also sounds like the crank may have been ground with different size journals.
While this may sound like a hack job, it may have just been repair work over its life. Do you have a tool, (caliper or micrometer) to measure the journals?

J

Re: Loose Rod
 

Have you talked to the shop that did the work??
Paul in CT

Re: Loose Rod
 

I do need to bring out the micrometers and do some measuring. Discovered the bearings are .030, and this is on new AER rods.

I have not talked to the shop yet. I want to try and solve this on my own, but it is looking like maybe not. I have some shims coming on the way as an option.

Re: Loose Rod
 

Are you getting tapered shims like these?
http://deckwartaperedshims.com/main-...oduct-info.php




Bob

Re: Loose Rod
 

I bought laminated shims from Brattons.
https://www.brattons.com/brass-conne...rod-shims.html

Re: Loose Rod
 

Chris,

one of the factors to making inserted bearing work properly is the deterministic nature of the design. The rod, or block bore is to a specific size and round within tolerance. This is done to make the insert pair conform and crush for proper retention, and resistance to spinning. By adding shims, you are in effect distorting the bore and more than likely will cause problems. I am quite certain that the AER rods are precision machined and sized for the bearing inserts. It is probably best to contact AER and get the bearing size information and then determine the course of action.

As I mentioned earlier, checking the radius clearance is paramount and not hard to do.

John