R.White

'26 engine knock

Recommended Posts

On ‎8‎/‎13‎/‎2017 at 4:40 PM, cahartley said:

Having, within the last few days, got my 1932 Chevrolet Confederate engine running I can tell you da bois at the Vintage Chevrolet Collectors Association warn that .002" clearance on a  194 six banger which has 2" rod journals WILL knock!

My Dodge had more than that before I checked the shims and it didn't knock.

Both have nearly identical rod oiling systems.

Go figure........ <_<

The minimum clearance is the .002-00 thousandths on a 2" crank, or not over .000-50 more.

 

I will guess at 99% that the knocks were caused by the Rods being out of Alignment.

 

Twist, Bend, and Offset.

 

Herm.

Share this post


Link to post
Share on other sites
On ‎8‎/‎13‎/‎2017 at 4:55 PM, R.White said:

Go figure indeed.  I was always under the impression that engines that relied on splash feed should have sufficient clearance for the oil to just flow in and out under gravity and that the introduction of pressure fed systems meant that closer tolerances could be achieved safely.  There is a certain logic  to it and that the reason we can go for closer tolerances now is that if synthetic oil is used it is not just better but thinner than the old straight oils.  I am always prepared to accept that I may have got it wrong but none of the other big end bearings are tighter than 0.002"... and they don't knock.  Why just this one?

 

Ray.

 

Bloo.  The main bearings have been a nightmare.  In a previous post I related how I couldn't get them closer than 0.003" without binding.  As I say, I think this crankshaft has suffered trauma at some time. 

 

That it runs at all is probably something of a miracle.:huh:

 

Ray.

Did you have the crank checked for being sprung?

 

Herm.

Share this post


Link to post
Share on other sites
On ‎8‎/‎14‎/‎2017 at 4:40 PM, R.White said:

Hi Bob.  On my engine the shells are trapped by the shims so cannot move around.  They are dead flush with the bearing cap and are quite a tight fit so need to be prised out.  There are also notches on the back which locate them.  As I see it, the shells cannot move in the rod when the bearings are bolted up.  I will look at it again, though, because thinking about it that might just be what is causing the knock if all the other bearings are quiet at 0.002".

 

Ray.

Has your rods been changed over to inserts, other wise they were poured solid.

 

Herm.

Share this post


Link to post
Share on other sites
On ‎8‎/‎15‎/‎2017 at 7:26 PM, MikeC5 said:

Hi Ray, I do know that for Model T engines, when new babbit is poured the bearings are set up very tight.  A friend of mine had his engine rebuilt by a long-time Model T specialist who was close enough that we could deliver the engine to him.  He showed us a completed short block he had on stand and let us try to turn it over with a long breaker bar.  It took considerable force to get it moving.  Instructions for starting it the first time required towing the car since it was too tight to crank by hand (our only other choice).  After running for several minutes it did loosen up enough to hand crank.  I think I would try tightening up the clearance on the offending rod big and and see if it changes things.  If it helps I might be tempted to tighten up the others too.  

Setting up Babbitt bearings that you have to use a long bar on is not acceptable to any engine, if your looking for any longevity out of it

 

When a crank, or rods are set that way, and the engine has to be pulled to turn it, the first thing that happens, is the bearing surfaces will soften from the friction, not a good thing.

 

At this time there is NO room for oil, so if the bearing doesn't burn out, it often scars, and if there are any oil grooves, or oil wells, the smear will deposit in the grooves, and turns hard again. Then this smear of Babbitt starts breaking off and runs through the bearing as bad as sand.

 

Why set a bearing so tight it has to struggle, to get its self free to turn.

 

A Model T we set at from .001-25 to .001-75, and you don't need any bar, and the crank you can turn with one hand on the flywheel flange after broke loose with the other hand.

 

Sadly, there is way more misinformation on Babbitting  out there then truth.

 

Thanks,

 

Herm.

 

.

Share this post


Link to post
Share on other sites
2 hours ago, herm111 said:

The minimum clearance is the .002-00 thousandths on a 2" crank, or not over .000-50 more.

 

I will guess at 99% that the knocks were caused by the Rods being out of Alignment.

 

Twist, Bend, and Offset.

 

Herm.

 

From the 1932 Chevrolet Book of Specifications.

Rods.jpg

Share this post


Link to post
Share on other sites
On ‎8‎/‎15‎/‎2017 at 9:10 PM, Bloo said:

I remember reading on some period publication, probably Dyke's Encyclopedia or maybe Audel's, about a machine used to "burn in" newly cast babbit bearings. The machine would spin the fresh engine with an electric motor until it spun freely. Sounds risky. I would want it to turn freely, if only barely.

 

 

 

 

Your right, they burnt bearings out, instead of in.

Share this post


Link to post
Share on other sites
59 minutes ago, cahartley said:

 

From the 1932 Chevrolet Book of Specifications.

Rods.jpg

This is just what I was talking about. Most listings, in bearing books will list a bearing from .000-50  on the low side to .003, or .003-50 on the high side. That is why some people get into trouble setting bearings. Now nobody in the right mind would set a bearing to .000-50, on a 2" crank, but they do, and they say, " But It Is In The Book" you would burn the bearing out. .001-50 is better, but you will still smear, or soften the Babbitt surface. Why have  the bearing push its self free. T clearance should be .002-00 to .002-50.

 

The thing is, when the bearing is broke in, it will be bigger then that.

 

Most people don't think, that when a .002-00 inch crank gets hot, they swell about .002-00, and more. So what happens, No room for oil, so it either pushes out, or burns out.

 

Try it your self. Mic a crank that is in shade, then lay it out side in the sun on a hot day. Then Mic it again, see the difference.

 

Thanks Herm.

 

KohnkeRebabbittingService.com

 

 

Share this post


Link to post
Share on other sites

The Chevrolet engineers were working on new engines, not rebuilding worn, bent & misaligned blocks. Maybe that might explain their ideas and our different takes on the information. I would send my engine to Herm any day.

Edited by JFranklin (see edit history)

Share this post


Link to post
Share on other sites
19 hours ago, cahartley said:

Yes Herm.......I'm sure the Chevrolet engineers didn't know what they were talking about.

 

 

7 hours ago, JFranklin said:

The Chevrolet engineers were working on new engines, not rebuilding worn, bent & misaligned blocks. Maybe that might explain their ideas and our different takes on the information. I would send my engine to Herm any day.

Mr. Cahartley, 000-50 to .001-50 is a long way on a 2" crank, from where it is going to end up to at least .003-00 thousandths clearance.in 1932, as most of the car companies done was to run the engine in, either by its self, or the whole car to loosen it up under an outside source of power.

So from .000-50 thousandths to .003-00 is .002-50 thousandths, so where is .002-50 thousandths of bearing surface going that  could have been used. It will go through Mains, Rods, cam bearings, cylinders, ect.

 

In my business, we hear all the time, can't turn the engine over, had to pull it and the rear wheels would slide. About 4 years ago a man with a Model T trying to start a new rebuild, blew two new rear  tires out.  

 

That was 1932 technology, it is not done that way today. If an engine builder were to set that clearance on a Babbitt engine today, and send it out, he would be doing it over.

 

It is the same with new pistons. The paper work that comes with the pistons will say, .002-00 to .002-50 on about a 4" piston. At that size it would score right away. So we give a 4" pistion .004-00 clearance, that is .001-00 per inch, and that works.

 

Herm.  KohnkeRebabbittingService.com

Edited by herm111 (see edit history)

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now