Burtz Block

[Terry Burtz Calif]

Quote:
Originally Posted by BRENT in 10-uh-C View Post
So allow me ask a question regarding thicknesses, ....would you rather buy a new set of tires that has 10/32" of tread depth, -or tires with 3/32" of tread depth?? It seems like someone would get 3X more mileage when they start with the 10/32" depth tires.

So if the same thought was applied to Model-A engine bearings, wouldn't someone get 3X more longevity out of a babbitted engine over a inserted engine if the same quality of bearing materials was used, and all mechanical parts were of equal specification and condition??




No. The thicker the Babbitt the more compressable it is, the more it compresses the more it fatigues and starts cracking and falling out.
That is why High performance and race engines use Tri-metal bearings.
Tri-metal bearings have a steel back , copper underlay to support the thin layer of Tin/Babbitt. The copper underlay is not nearly as compressable as Babbitt and as a result less fatigue and longer bearing life.
Bill

PS Read up on Clevite 77 bearings.




Bill,

Your answer to Brent's question is correct. Thank you.

The new engine uses 12 pairs of Clevite CB-745P standard size tri-metal bearings.

For those that want to learn about modern bearings, please see: Clevite “Light Vehicle Engine Bearings” catalog EB-20-18 (https://www.mahle-aftermarket.com/m...s-and-literature/engine-bearings/eb-20-18.pdf)

 

[BRENT in 10-uh-C]

No. The thicker the Babbitt the more compressable it is, the more it compresses the more it fatigues and starts cracking and falling out.
That is why High performance and race engines use Tri-metal bearings.
Tri-metal bearings have a steel back , copper underlay to support the thin layer of Tin/Babbitt. The copper underlay is not nearly as compressable as Babbitt and as a result less fatigue and longer bearing life.

Terry, to an extent what you are saying is correct, ...and generally this issue as you are describing is found when improper methods are performed in the casting & machining process by rebuilders.

Most rebuilders today use WAY more shims (-i.e.: thickness) than what Ford used originally, and many rebuilders fail to peen the freshly cast metal for the purpose of compacting it simply because they don't know to do that, -or it is an effort to save time. Burnishing also falls into this category. As you correctly stated, this often causes fatigue & cracks in the bearing. When the proper composition of babbitt is used, and when process is done correctly, the additional compaction, fatigue, and cracking is not seen. As we have discussed above, engines with nearly triple the compression ratios have utilized poured and cast bearings with many years of great service to their credit. In the scenario of using an insert bearing that has the same compaction as the cast bearing, the wear should be the same with little to no difference between the two types of bearings, HOWEVER when the babbitt on the insert shell has worn 0.002", that bearing is reached the end of its' life cycle whereas the cast bearing has the ability to remove one or both shims and continue many more miles.

 

[bbrocksr]

Terry, to an extent what you are saying is correct, ...and generally this issue as you are describing is found when improper methods are performed in the casting & machining process by rebuilders.

Most rebuilders today use WAY more shims (-i.e.: thickness) than what Ford used originally, and many rebuilders fail to peen the freshly cast metal for the purpose of compacting it simply because they don't know to do that, -or it is an effort to save time. Burnishing also falls into this category. As you correctly stated, this often causes fatigue & cracks in the bearing. When the proper composition of babbitt is used, and when process is done correctly, the additional compaction, fatigue, and cracking is not seen. As we have discussed above, engines with nearly triple the compression ratios have utilized poured and cast bearings with many years of great service to their credit. In the scenario of using an insert bearing that has the same compaction as the cast bearing, the wear should be the same with little to no difference between the two types of bearings, HOWEVER when the babbitt on the insert shell has worn 0.002", that bearing is reached the end of its' life cycle whereas the cast bearing has the ability to remove one or both shims and continue many more miles.

Hey Brent, Terry didn't say that , I did and Terry agreed.
Bill

 

[nkaminar]

From the reference listed by Terry above, Bearing life versus Babbett thickness. Even though the bearing life is maximum at minimum thickness, some thickness is needed for various reasons.

What the graph shows is that an insert bearing will last 10 times as long as poured bearings (250 vs. 25). (Depending on how you read the graph it could be 8 times as long, but still longer.) Also, based on my experience on various engines, when the insert bearings need replacing, the journal is normally still good and new insert bearings can just be installed.

What the reference also says, in so many words, is that an oil filter is important to have. And that proper assembly is very important.

 

[Terry Burtz Calif]

Terry, to an extent what you are saying is correct, ...and generally this issue as you are describing is found when improper methods are performed in the casting & machining process by rebuilders.

Most rebuilders today use WAY more shims (-i.e.: thickness) than what Ford used originally, and many rebuilders fail to peen the freshly cast metal for the purpose of compacting it simply because they don't know to do that, -or it is an effort to save time. Burnishing also falls into this category. As you correctly stated, this often causes fatigue & cracks in the bearing. When the proper composition of babbitt is used, and when process is done correctly, the additional compaction, fatigue, and cracking is not seen. As we have discussed above, engines with nearly triple the compression ratios have utilized poured and cast bearings with many years of great service to their credit. In the scenario of using an insert bearing that has the same compaction as the cast bearing, the wear should be the same with little to no difference between the two types of bearings, HOWEVER when the babbitt on the insert shell has worn 0.002", that bearing is reached the end of its' life cycle whereas the cast bearing has the ability to remove one or both shims and continue many more miles.

Brent,

I agree with some of what you say, but believe that your reply is directed to the comments made by Bill, not me.

Please keep in mind that the inherent design problem in a Model A engine is the flexible and under-supported crankshaft.

Insert bearings are not new. The Dodge "Fast 4" engine built in 1927 and 1928 was a 4 cylinder, 5 main bearing design that used Federal-Mogul insert 6345B for the connecting rods and Federal-Mogul main bearing set 277M.

Terry Burtz

 

[Terry Burtz Calif]

From the reference listed by Terry above, Bearing life versus Babbett thickness. Even though the bearing life is maximum at minimum thickness, some thickness is needed for various reasons.

What the graph shows is that an insert bearing will last 10 times as long as poured bearings (250 vs. 25). (Depending on how you read the graph it could be 8 times as long, but still longer.) Also, based on my experience on various engines, when the insert bearings need replacing, the journal is normally still good and new insert bearings can just be installed.

What the reference also says, in so many words, is that an oil filter is important to have. And that proper assembly is very important.

Neil,

Thanks for looking at the Clevite catalog and displaying the graph.

Sometimes thicker is not better and results in a shorter life.

 

[Synchro909]

Ok. Maybe others will chime in, but all of the 7:1 heads I have messed with have a lowered roof in the combustion chamber simply because you cannot take enough off of a 5.5 head without getting piston interference. If the 'squish' area over the piston is minimal, it is my experience this will cause detonation issues where setting for optimum timing is a struggle as you have suggested.

As I'm sure you, and most others will agree, using a compression gauge to determine the ratio is rarely accurate. To confirm this, think about when you are taking the reading. Most will crank the engine over a minimum of 4-5 times while obtaining the reading, and each time the piston makes a cycle, the gauge reading gets higher and higher. The first time the piston comes up is more likely the closest correct reading on the gauge. The only accurate way for most people to determine a C/R is to CC the chamber and calculate gasket areas, etc.

I get no piston interference - yet but I don't know how many times I can flatten the head. I'm sure a lot of the increased CR is due to the over sized bores. (0.060" over)
Agreed on your comments re compression readings. The figure I quoted was after your 4 or so cycles so maybe the true number is not so high.

On another matter, have you had experience with the rear (inserted) main bearing starving for oil? I have seen a couple of examples of the insert being pretty chewed up. Fortunately, the journal was OK and a new insert was all it took. Before fitting them, I cut a spiral groove in he top insert to get oil towards the back of the bearing. I stopped the groove about 10mm (3/8") from the edge of it. I run 20w50 grade oil and I'm thinking that something like 15w40 might be better. Watchya reckon?

 

[Hipopinto]

Guys this is giving me tons of info I really appreciate all of this

Thanks again
Dave

 

[jack backer]

Terry is your engine fully pressurized?

 

[Terry Burtz Calif]

Terry is your engine fully pressurized?

Jack,

Yes, the "New Engine" has 17 pressure-fed bearings and all oil passages are drilled in cast iron bosses. There are no fittings or loose oil tubes.

The 17 pressurized bearings include 5 main bearings, 5 camshaft bearings, the rear main thrust bearing, 4 connecting rod bearings, the camshaft thrust bearing at the front of the cylinder block, and the camshaft plunger thrust surface.

More details can be found at www.modelaengine.com, www.burtzblock.com, and https://www.facebook.com/groups/1123377268114692

This thread has opened a can of worms with those that believe in the original thick-poured Babbitt bearing design with a flexible crankshaft and those that understand modern engine design.

 

[HotRodHell]

Jack,

Yes, the "New Engine" has 17 pressure-fed bearings and all oil passages are drilled in cast iron bosses. There are no fittings or loose oil tubes.

The 17 pressurized bearings include 5 main bearings, 5 camshaft bearings, the rear main thrust bearing, 4 connecting rod bearings, the camshaft thrust bearing at the front of the cylinder block, and the camshaft plunger thrust surface.

More details can be found at www.modelaengine.com, www.burtzblock.com, and https://www.facebook.com/groups/1123377268114692

This thread has opened a can of worms with those that believe in the original thick-poured Babbitt bearing design with a flexible crankshaft and those that understand modern engine design.

I sold my last model A about 8 years ago and recently became interested in having a Model A again. Doing a little research i came across your improved engine. I then became real serious about an A or B car. I even put a 600hp car on the market.
I believe in the superiority of your block and internal improvements.

 

[4bangerbob]

I get no piston interference - yet but I don't know how many times I can flatten the head. I'm sure a lot of the increased CR is due to the over sized bores. (0.060" over)
Agreed on your comments re compression readings. The figure I quoted was after your 4 or so cycles so maybe the true number is not so high.

On another matter, have you had experience with the rear (inserted) main bearing starving for oil? I have seen a couple of examples of the insert being pretty chewed up. Fortunately, the journal was OK and a new insert was all it took. Before fitting them, I cut a spiral groove in he top insert to get oil towards the back of the bearing. I stopped the groove about 10mm (3/8") from the edge of it. I run 20w50 grade oil and I'm thinking that something like 15w40 might be better. Watchya reckon?

Increasing the Bore size increases the compression ratio, A standard bore engine verses a bored cylinder bore has a smaller volume then oversized bores and will result in a lower compression ratio. A standard bore model A engine with a 6 to 1 cylinder head will produce a compression ration of approximately 6.38 on an engine bore .125" oversize.

 

[Dodge]

I don't know how many babbitt motors have gone 400,000 miles but I know of several
insert bearing motors that have....

 

[Synchro909]

I don't know how many babbitt motors have gone 400,000 miles but I know of several
insert bearing motors that have....

400,000 miles would be a modern motor with hardened bores, thin rings and al the other things engineers have done to extend their life. I bet NO model A engines, inserts or no will have gone close.
That said, 400,000 miles is chicken feed for a decent truck engine many of which have (as has been said) Babbit bearings.

 

[jack backer]

Full pressurization is the key for insert bearings, it keeps them clean and cool.My observations about insert and babbit bearings was predicated on the stock A splash and gravity method of lubricating rod and main bearings.

 

[nkaminar]

Synchro, Just curious. What modern truck engines have poured bearings? I assume you meant poured bearings. Or do you mean antique truck engines? I know modern Diesel engines can go a million miles or more and I assume they are all insert bearings. Please contribute to my education.

By the way, there were some photos of cars in the 60's in Australia Surfer's Paradise recently in The Old Motor. https://theoldmotor.com/?p=191760