Engine Bearing Failure

[Trevor]

Originally Posted by TomsSVX

Assuming the bolts that have seen thousands of heat cycles are equally different from their OEM specs... Not to mention the stock rods are heavier than they could be and their weights I am sure are not quite as equal as many would prefer. it would be who of whomever is building an engine to simply replace them with better ones. Tom

I was assuming that here an engine build in preparation for power modifications is involved, in which case surely new bolts would be fitted. You have not got the point.

When a bolt is not stretched adequately, room is left for further stretching under load. This results in continuous movement and hence fatigue. Manufacturers tolerances can often be too conservative.

My source of information, the late Bruce McLaren, as a result of a conversation relative to his experience gained through his company's successful racing in the US and Europe. He was describing a specific fix for what had become a serious problem.

[TomsSVX]

Originally Posted by Trevor

I was assuming that here an engine build in preparation for power modifications is involved, in which case surely new bolts would be fitted. You have not got the point.

When a bolt is not stretched adequately, room is left for further stretching under load. This results in continuous movement and hence fatigue. Manufacturers tolerances can often be too conservative.

My source of information, the late Bruce McLaren, as a result of a conversation relative to his experience gained through his company's successful racing in the US and Europe. He was describing a specific fix for what had become a serious problem.

The point missed is that the rod bolts are not serviced separately by Subaru. in which case aftermarket fasteners would need to be installed. At this point, an engine built for power, it is my recommendation not to bother fitting new hardware to an old rod, rather install better rods which come with better fasteners.

Tom

[NeedForSpeed]

Originally Posted by TomsSVX

The point missed is that the rod bolts are not serviced separately by Subaru. in which case aftermarket fasteners would need to be installed. At this point, an engine built for power, it is my recommendation not to bother fitting new hardware to an old rod, rather install better rods which come with better fasteners.

Tom

Point well taken, also, installing new bolts in old rods, especially bolts from another manufacturer, distorts the rod housing, the rods would require resizing to insure roundness.

[Trevor]

Originally Posted by NeedForSpeed

Point well taken, also, installing new bolts in old rods, especially bolts from another manufacturer, distorts the rod housing, the rods would require resizing to insure roundness.

Provided the exactly correct sized bolts are installed in old rods without any other alteration, in no way can this alter the angle or relative degree of compression exerted between the two sections involved and as a result cause any new form of distortion.

The point made within my posts has now been completely misconstrued.

[NeedForSpeed]

Originally Posted by Trevor

Provided the exactly correct sized bolts are installed in old rods without any other alteration, in no way can this alter the angle or relative degree of compression exerted between the two sections involved and as a result cause any new form of distortion.

The point made within my posts has now been completely misconstrued.

I have remanufactured thousands, yes thousands of connecting rods. The only 'exactly' correct bolt with an exact 'press' fit is the OEM, if you are lucky. My experience is that aftermarket bolts often vary, many requiring a great deal of force via press to install. Granted, not much harm in that area of the rod bearing, and likely all would be okay, but a perfectionist I am. If I changed bolts, I would carefully measure the rod, before, and after.

I was not responding to your posts, only to Tom's last post mentioning the fact that buying new rods was a better deal in the long run than purchasing better bolts for a stock rod. thanks

[Trevor]

Originally Posted by NeedForSpeed

I have remanufactured thousands, yes thousands of connecting rods. The only 'exactly' correct bolt with an exact 'press' fit is the OEM, if you are lucky. My experience is that aftermarket bolts often vary, many requiring a great deal of force via press to install. Granted, not much harm in that area of the rod bearing, and likely all would be okay, but a perfectionist I am. If I changed bolts, I would carefully measure the rod, before, and after.

I have to say that in view of your experience, I am concerned that you would under any circumstances, consider forcing a bolt into a restrictive space as there will be immediate distortion, with extra occurring at operating temperature.

I was not responding to your posts, only to Tom's last post mentioning the fact that buying new rods was a better deal in the long run than purchasing better bolts for a stock rod. thanks

Sorry if I inferred that you had caused this problem. This was not intended.

[NeedForSpeed]

Originally Posted by Trevor

I have to say that in view of your experience, I am concerned that you would under any circumstances, consider forcing a bolt into a restrictive space as there will be immediate distortion, with extra occurring at operating temperature.

This is exactly the point, rod bolts typically have knurled shanks, a press fit is intended, into a 'restrictive space'.

When new bolts are driven in, due to interference fit, when the rod cap is installed and torqued to specs, the rod can be distorted compared to the original production. The rod housing may not be perfectly round or measure to spec dimensionally as desired. If you understand the distortion, you should grasp the reason I gave to have the rod re-machined.

Any time a fastener that secures a housing, the housing should be re-measured and re-machined accordingly. The intent of aftermarket rod bolts is more clamp load, could that have an effect on the housing? Of course it does.

A round and true-to-spec rod is necessary for bearing life. Sometimes the focus is only on measuring the crankpin and the rod bearings. The rod housing has a spec that is carefully measured by professional engine builders.

[TomsSVX]

Every conn rod stud, and I do mean stud not bolt, is pressed into the rod. All of them...

Only conn rod bolts are not, and even then they use a wave type design to align the two halves.. that is unless they use dowels of some sort built into the rods themselves like the STi rod and Eagle's method of hollow alignment shells.

This again, one of many reasons NOT to use stock con rods in a built motor... So why try to state a case to the contrary?

Tom

[Trevor]

Originally Posted by NeedForSpeed

This is exactly the point, rod bolts typically have knurled shanks, a press fit is intended, into a 'restrictive space'.

When new bolts are driven in, due to interference fit, when the rod cap is installed and torqued to specs, the rod can be distorted compared to the original production. The rod housing may not be perfectly round or measure to spec dimensionally as desired. If you understand the distortion, you should grasp the reason I gave to have the rod re-machined.

This has turned up some information that will be of general interest and it is therefore worth continuing as there are several doing engine rebuilds on a hobby basis.

I now note that the typical rod bolts are knurled and a press fit is intended. OK if the knurling is such that there is no significant forced expansion, but to a degree requiring a power pressed fit appears stupid. The mind boggles at the sense of this and indeed the actual purpose or need for the knurling and an interference fit, which can distort the rod. What exactly is the manufacturers reasoning?

I exactly understand “distortion” and therefore ask, why accept that there will be distortion and re-machine the rod to compensate? In circumstances where no other bolt is obtainable, why not remove the knurling so that the bolt is free floating and all is correct? Raised knurling can have had no beneficial effect in respect of bolt strength. Surely no one uses these bolts in a modified engine.

[Trevor]

Originally Posted by TomsSVX

Every conn rod stud, and I do mean stud not bolt, is pressed into the rod. All of them...

Only conn rod bolts are not, and even then they use a wave type design to align the two halves.. that is unless they use dowels of some sort built into the rods themselves like the STi rod and Eagle's method of hollow alignment shells.

This again, one of many reasons NOT to use stock con rods in a built motor... So why try to state a case to the contrary?

Tom

There has previously been no previous mention of a conn rod stud.

Furthermore none of this has anything to do with my original post and comments, which remain valid and accurate. This discussion is for the birds, I leave you to it.

[Cam]

I was advised to reuse my stock rods, and NOT use tri metal bearings. I used bearings supplied to me by LAN. So we shall see whether or not the stock rods hold up in a build. 11:1 compression ought to figure it out real quick...

When the number 5 bearing fails in our engine, I have a feeling it is an oiling issue. Possibly the Rod in Desertrunners engine can be carefully inspected and ultrasound-inspected to look for any abnormalities in the material of the rod. I would think that there should be a non-destructive way to find out if the rod or the fasteners themselves were distorted. I think it would be worth the money to find out if possible.

[TomsSVX]

Originally Posted by Trevor

There has previously been no previous mention of a conn rod stud.

Furthermore none of this has anything to do with my original post and comments, which remain valid and accurate. This discussion is for the birds, I leave you to it.

We are talking about the EG33 which is equipped with conn rod studs... WTH are you going on about??

Simply admitt, if you were building a high revving engine, you would as soon switch to a better rod than fiddling with inferior bits for no good reason other to make an argument and maybe save $300 on a multi-thousand dollar engine... Making sense anytime soon would be who of you

Tom

[TomsSVX]

Originally Posted by Cam

I was advised to reuse my stock rods, and NOT use tri metal bearings. I used bearings supplied to me by LAN. So we shall see whether or not the stock rods hold up in a build. 11:1 compression ought to figure it out real quick...

When the number 5 bearing fails in our engine, I have a feeling it is an oiling issue. Possibly the Rod in Desertrunners engine can be carefully inspected and ultrasound-inspected to look for any abnormalities in the material of the rod. I would think that there should be a non-destructive way to find out if the rod or the fasteners themselves were distorted. I think it would be worth the money to find out if possible.

I know what you were advised. Different strokes for different folks.

Tom

[Cam]

It is important I point out that my engine will go to 7k rpm max. Any higher and there is no question I would have gone with Eagle Rods. I do not like how others have had so many cooling problems and bearing failures when they push the rotating speeds.

[TomsSVX]

Nature of the modifying beast I guess... One thing to take into consideration as well... You are not going to push more horses out of these engines and expect them to run 100k trouble free... Its less about picking the parts that will last the longest and more about the parts that will do the job the best.

Tom