6.2 L Block Stripped threads

[Bojangles]

I have a 6.2 l which has 2 maybe 3 stripped head bolt threads in the block.

Has anyone used recoil thread repair system in this application?

What method is recommended beside the above ?

Thanks

[DmaxMaverick]

You may get away with a thread repair if you use studs. Otherwise, you won't be able to torque them, successfully. There's not enough material to use full inserts (Lock 'n Stitch, etc.) without having other issues, sooner or later. One stripped head bolt thread usually spells doorstop. 2 or 3 is a real stretch.

[ronniejoe]

I ran into problems with stripped deck threads on a 6.5. I had five strip. I repaired 33 of the 34 holes with Helicoil inserts. On one, which was really bad, I used a solid threaded insert. I am using studs. There is plenty of material in the deck to use solid inserts if you need to as long as the insert isn't too large. I Loctite all of them in the deck so they don't move.

You must be very careful if you do this by hand yourself to maintain perpendicularity with the deck surface. I used an old head gasket as a guide to drill and then tap each hole as shown in the photo.5982

I have two performance engines in process right now that I am installing Helicoils in from the get-go so the problem doesn't happen again. On these blocks, I had the machine shop set them up in the mill and do them all at the same time. They are much better on perpendicularity that way. My engines run boost approaching 30 psi and make lots of power.

[ronniejoe]

Here is a photo of the solid insert after installation.

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[ronniejoe]

Otherwise, you won't be able to torque them, successfully.

If the insert, Helicoil or otherwise, is secured with Loctite, there is no reason that a standard head bolt cannot be used and successfully torqued. I have engineered Helicoils into gas turbine aerospace engine gearboxes to both repair threaded holes and as OEM application to protect threads in magnesium from stripping. Those applications have accumulated literally millions of flight hours by now. Installed correctly, the repaired hole is better than original when in softer materials (gray iron, magnesium, aluminum, etc.). This is because the threads in the parent material are larger which increases their contact area. The inserts are steel which is stronger. Therefore, the stresses in the parent material from the clamp load are lower than in an unrepaired hole.

[DmaxMaverick]

More power to ya. Torque conventional head bolts on a Heli-Coil, if you can. Then run them up to power with 30# boost, or 7 for that matter. If they're still holding on at that point, start the countdown. My comment regarding successful coil-type thread repairs was specific to using studs, which can work. I have zero confidence using coil-types and conventional head bolts.

I'm very familiar with hardened fastener thread applications in softer materials, such as aluminum and magnesium. I have a detailed experience working closely with Grumman and Vought during my military hitch, keeping near-obsolete airplanes flying with a diminishing core component supply. I've authored component reclamation and repair procedures, and CMM/IPB updates, primarily specific to flight controls and redundant systems. Much of it deeply involved fastener thread repair, and more specifically, corrosion abatement, primarily responsible for fastener thread failure, among others. None of my command level citations and commendations mentioned the (likely) tens or hundreds of millions of tax dollars my collaborated efforts saved you. The only practical difference between this, and automotive head bolt threads is the scale. The principals are exactly the same.

[ronniejoe]

My direct experience involves the Allison Model 250 turboshaft and turboprop family of engines, the Allison T56 family of engines, The Allison AE2100 family of engines, the Allison 601 industrial engine, and others. The 250, T56, and 2100 engines are all in service in military applications. These engines help to keep you free. I also put the first lines on paper for the LiftFan system for the current F35B Joint Strike Fighter. At the time that effort was heavily classified and required a Secret Special Access Required clearance. I'm currently part of a team reverse engineering a large 45 MW industrial gas turbine engine for an overhaul shop that wants to start making their own parts to support their operation. We could argue all day about experience.

My question to you is, have you ever repaired a head bolt hole in the deck of a 6.5 Diesel -- any engine for that matter? You gave some very authoritative sounding advice saying that it was impossible to do and shouldn't be attempted -- "doorstop" comes to mind. All I did is explain that I have actually repaired head bolt holes in 6.5 Diesel engines. I provided photographic proof that I did it. That engine is running fine. It runs high boost and makes high power. I stated that I use studs. I never said that it was safe to use factory bolts at those boost and power levels. I did say that there is no reason this gentleman couldn't execute the repair using standard bolts. If he is running high boost, I would not recommend it.

It's one thing to say, "You know, I've never tried it, but it doesn't seem wise to me." It's another thing entirely to have never tried it and say, "There's not enough material to use full inserts (Lock 'n Stitch, etc.) without having other issues, sooner or later. One stripped head bolt thread usually spells doorstop. 2 or 3 is a real stretch." There is enough material to use a full insert. I've done it. It works. I tried to provide a little background so that the fellow could know that I am not just whistling Dixie. I'm sorry that you're that sensitive. I didn't attack you or attempt to insult you. I just showed that it can be done, because I have done it.

[DmaxMaverick]

I have done it, mostly successful, on smaller engines, but would not on the larger, to include the 6.2 or 6.5. I have seen failures on much lesser applications. The math doesn't add up. Torque requirements are too great. I'm not questioning your competence or experience, and have no doubt you'll stand behind your workmanship. Just saying the practice is ill-advised, despite your success.

[ronniejoe]

The math doesn't add up. Torque requirements are too great.

That's funny. I can do math, too, and it does add up. I've analyzed the repairs, calculated the stresses, and put the repairs into practice.

A little historical tale: I worked for Allison from 1983 to 1998. When I first started, it was part of the Detroit Diesel Allison Division of General Motors (I was informed once by a person here that Detroit Diesel was not GM when the 6.2 L was designed. That is factually inaccurate. I worked for Detroit Diesel Allison in 1983, just a couple of years after the design effort for that engine and in its early production run.) Shortly after I started, GM reorganized and made the gas turbine operation a separate entity called Allison Gas Turbine Operations. A few years after that, we were elevated to full division status as Allison Gas Turbine Division. Around 1993, GM sold Allison Gas Turbine Division to a group of investors called Clayton Dubelier and Rice. The name became Allison Engine Company (a throwback to the early 20th century before GM acquired Allison). In 1995, Rolls-Royce bought Allison Engine Company and made it part of their North American Aerospace Group. The Allison Engine Company name was retained for about two years, then it became Rolls-Royce Corporation, a wholly owned subsidiary of Rolls-Royce Plc. In the mid to late 1980s, there was an engine demonstrator program called the Model 578-DX, which was flown on a McDonnell-Douglas MD-UHB PropFan demonstrator aircraft. Here is a picture of it in flight over the Sierra Nevada.

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This demonstrator engine used an Allison Model 571 core (XT701 in military parlance, which was developed for the Boeing Heavy Lift Helicopter program in the 1970s) which produced over 7000 hp. The thrust requirements for the counter rotating, advanced propfans dictated required power of about 13,000 hp at takeoff. To achieve these levels of power with the 571 core, a 3-stage boost compressor with variable geometry guide vanes was designed and manufactured for the engine. During testing of the boost compressor, Allison engineers explored the full range of operability of the variable geometry, closing the vanes to nearly 80%, which reduced the flow through the compressor. They found that power required to drive the compressor could be modulated down to under 50% of full open vanes. There were operational requirements for the test flight that required some power modulation (not the full amount tested) for the boost compressor. I don't remember all of the details because it has been 30+ years ago. However, this modulation capability was demonstrated in flight on the modified McDonnell-Douglas MD-80 in the photo above. It was conceived. It was designed. It was ground tested. It was demonstrated in flight. It worked. As a side note, I wrote my fifth year undergraduate thesis on the design of a new single helical gear train using ribbed cup tapered roller bearings for the gearbox for this engine.

Later in 1989 and 1990, I used the data collected from that boost compressor testing program during my work to do the preliminary design of the LiftFan clutch and fan itself. I was responsible for the fan mechanical design and for the clutch design at the beginning of that program. I also was responsible for pulling together the work other people did and getting it compiled into report documents, so I became very familiar with all of the engineering decisions that went into that PD work. I also concepted a vane box, thrust vectoring nozzle assembly for the LiftFan exhaust. The modulation capability was integral to my strategy for making the clutch package small and light enough to make the whole LiftFan concept work. We scaled the data from the 578 boost compressor to the 48" diameter size of the LiftFan. I had curves of power absorption, including inertia and windage, for the fan for varying speeds and variable geometry vane settings. By using the full closed data, we could reduce the power demand that the clutch had to reject as heat during an engagement by closing the variable geometry to modulate the flow and thereby modulate the power demand. I was shooting for an engagement time of roughly 10 s to accelerate the fan from stopped to about 60% speed with full closed VGV. At this point, a mechanical spline drive was engaged to relieve the load on the clutch and accelerate to full speed and power afterward. The energy dissipation during those engagements was huge, as I was rejecting about 2.5 hp/in^2 of friction interface area -- about 2.5 times the previously demonstrated capability. I ended up designing in Carbon-Carbon composite clutch disks that operated dry to be able to handle the heat rejection.

So that is the status of the LiftFan project when Rolls-Royce bought the company in 1995 (I did my work from 1989 - 1991 on the project. I had moved on to the Model 250 program by the time they bought the company.). The very arrogant British engineers from Rolls came in and reviewed our design, which had already been reviewed and accepted by Lockheed, and promptly told us that we couldn't do the power modulation with variable geometry vanes that we were designing around. Our compressor design guys pulled out all of the test data and showed the Rolls guys the work we did and the data we collected and showed them video of the flight testing. The Rolls engineers said it was impossible. They said that our data collection was bad and that we didn't know what we were talking about. Again, we said, "It flew". They literally said, "No, it didn't". I knew right then that I needed to leave Rolls-Royce. I left in 1998 and went to work for Caterpillar.

See if you can draw any parallels from this story to current events.

[ronniejoe]

...but would not on the larger, to include the 6.2 or 6.5.

So, the answer to my question is no, you haven't repaired a 6.5 deck thread. OK. I guess it can't be done, then. I must have been dreaming, just like I dreamed about that boost compressor test data.

[DmaxMaverick]

So, the answer to my question is no, you haven't repaired a 6.5 deck thread. OK. I guess it can't be done, then. I must have been dreaming, just like I dreamed about that boost compressor test data.

I have never repaired a 6.5 deck thread with a heli-coil, because I wouldn't. I've repaired plenty of others with them, and have seen a good number of failures. I may have been mistaken about full inserts, but the material thickness doesn't appear sufficient, at least in much of the block. More than one on a cylinder increases the odds of failure. Using studs changes a lot of that, which is what you say you are using. Using a coil insert and conventional head bolts is a recipe for failure, and I'll stand on that. I've seen it, and done it, on much lesser applications. Sometimes it worked. Sometimes it didn't.

[ronniejoe]

I have never repaired a 6.5 deck thread with a heli-coil, because I wouldn't. I've repaired plenty of others with them, and have seen a good number of failures. I may have been mistaken about full inserts, but the material thickness doesn't appear sufficient, at least in much of the block. More than one on a cylinder increases the odds of failure. Using studs changes a lot of that, which is what you say you are using. Using a coil insert and conventional head bolts is a recipe for failure, and I'll stand on that. I've seen it, and done it, on much lesser applications. Sometimes it worked. Sometimes it didn't.

OK, so you wouldn't. You would simply throw away a block that you had invested thousands of dollars into. Glad to know. Did you even look at the picture I posted? Since my repairs have not experienced the catastrophic failures that you predict, I think I will stand by my decision to do it. If I were you, the engine that I use in my truck every day would be in the scrap yard right now. It is not. It is running in my truck and working very well. But with the British mentality, I guess it really isn't and I am dreaming again. I did it. It works, but you say it doesn't, so I guess I didn't. I'm sure that I've done lots of things with machines that you wouldn't. Maybe you haven't been performing the repairs properly if you have such a high incidence of failure.

I really enjoy doing things mechanically that other people say cannot be done. It's how I make my living. But maybe I don't. I don't know. Now I'm confused. There is a lot of gas-lighting going on everywhere these days on lots of subjects.

[ronniejoe]

Here's another historical tale: After I left Caterpillar and went into business for myself as an engineering consultant, Caterpillar hired me under contract to work on several projects. One was an attempt to break into the on-road transmission market for applications like motorhomes, trash trucks, medium duty box trucks, fire engines, etc. That market is dominated by Allison Transmission. I was hired to help analyze the Allison and offer expertise on helping them get a competitive transmission to market. They were starting with their articulated dump truck transmission as the baseline. They had procured four or five Allison 3000 series transmissions for evaluation, disassembly, and comparison. I was standing with a group of Caterpillar engineers on the floor in Building KK in East Peoria in late summer 2004 with their ATD transmission and an Allison on the table in front of us. They had weighed the transmissions and the comment was made, "We need to go on a diet. Our transmission is significantly heavier than the Allison. Does anyone have suggestions on where to start?" I spoke up and said, "Well, your housing is made from cast iron. You should redesign it to be made from cast aluminum." There were a bunch of dumbfounded looks for several seconds. Finally, one of their engineers spoke up and said, "You can't make a transmission housing out of aluminum!" I looked equally dumbfounded and reached up and flicked the housing of the Allison with my finger and said, "Allison figured out how to do it. That's what this housing is made from." The reply was, "Well, we​ wouldn't do that." Needless to say, their project failed after they wasted a lot of money trying but refusing to listen.

[Robyn]

Hmmmmm

Was the engineer who said "We woudn't do that" (Using aluminum) an old fart with a serious attitude ????

Gawd....Aluminum has been used as an auto tranny case material for decades and decades and by nearly every manufacture on the planet.....

Somebody was just being obstinate me thinks.....

[Bojangles]

Thanks for all your comments/advice.
From what I can understand the best way is to use solid inserts and studs. Or solid inserts and bolts.