Blown Head Gasket - M38

[RonD2]

Thanks Wes. Yes, all above posted by you about the rear main seal previously noted when posted 1st time around. Emphasis acknowledged, and I'll be sure to point out to machinist! Thanks.

Your opinion: is that a rope seal or not?

Your opinion: is any backlash between crank and cam timing gears acceptable or advisable? (I couldn't find anything on it in the TM) I imagine the machinist can tell me as well.

The four crankshaft flywheel bolts fell out with fingers. The two tapered dowel studs are in there pretty tight (no amount of tapping I did with nuts on them broke them loose, but I didn't get crazy on them). The thread condition and apparent age of all 6 are questionable enough for me to replace all. I'll ask the machinist to take the two studs out and install a new pair. I'll replace the other 4 bolts myself. New nuts and lock washers all around.

The 5th sentence in my copy of TM9-1804A paragraph 81 on page 83 says: "Install the four bolts and two tapered studs in the flywheel flange on the crankshaft."

If your point was not to forget this step unless I want to remove and replace the crank more than once ---- thanks! Although I do have "half-heimers" (can't remember sh*t half the time) I've read plenty of threads about consequences of forgetting........I'll let you know how it goes.

[wesk]

If a guy learns to use the books when rebuilding his jeep and he learns to make notes in them when he learns more elsewhere than the book had told him and he underlines important stuff that if overlooked leads to a lot of re-doing, then he should fair well in this business called restoration.

Backlash should be minimal. There should always be a .001 or so for lubrication . If it allows the gear teeth to hammer each other causing a lot of wear then the fiber cam gear is probably worn excessively. It's common for there not to be a spec for this measurement and since common sense comes with experience, this experience comes two ways; book learning & OJT. If you would like to get a better understanding on the design aspects of gear backlash here's a easy to read short treatise on the topic:
https://www.machinedesign.com/motion-co ... r-backlash

Had you carefully reviewed my photo album and the manuals you would already know that your seal is not a rope seal.

[RonD2]

Delivered the disassembled motor (block, head, and all the guts) to the machine shop yesterday morning.

After a tailgate inspection and a 30 minute discussion, we unloaded it all --- a very good sign.

[RonD2]

Not much in the manuals on the oil strainer, except to say "clean thoroughly", which I did by soaking and sloshing it around in a bucket of diesel (which turned black). Is it really clean? Must be.

Nothing on disassembly except to pull the cotter pin and remove the support tube. No joy searching the forum on how to uncover the screen for a look-see.

The sheet metal cover over the screen has four clips holding it on (12-3-6-9 o'clock). It looked like if I carefully bent the one lone tab at 12 o'clock up a little, the other three would come free by tapping the cover to slide off in the opposite direction. Did that, careful not to deform the sheet metal any more than necessary. It popped right off --- and showed me 50 years of black gold....

I'm glad I looked.

[RonD2]

I can get a pair of replacement tapered dowel bolts to mate my crankshaft and flywheel for about the same cost as a pair of straight dowel bolts. Keeping the tapered bolts saves me from having to drill the flywheel for straight dowels.

I searched for the reason (and possible benefits) of "upgrading" to straight dowel bolts and it's not apparent to me. Better performance? Last longer? Maybe the straight dowels are just cheaper to make?

Am I missing something? If it's 6 of one and half-dozen of the other, I think I'd rather just stick with the early tapered bolts and not have to drill my 97-tooth flywheel.

Your advice appreciated as always!

[wesk]

97 tooth???? Interesting. No sense in trying to make it correct at this point! From an engineering standpoint "6 of one & a half dozen of the other" makes absolutely no sense. Had there not been an improvement that dictated the cost to change they would not have done it.

Anytime you have a tapered joint and start removing and re-installing wear will set in. This wear leads to loose tapered studs which by coming loose alone will cause some nasty damage.

[RonD2]

Thanks Wes (I think). Not sure why you pull out the guns every time I ask what I think is a reasonable question, from somebody who doesn't have anywhere near the experience that you do. No matter. Maybe it's me. Just wish I could get off your sh*t list once in a while.

I'm not building the perfect M38. Can't afford it right now. Yes, 97-tooth flywheel. Not a crime. Remember my post about having an early bell housing? So long as what I have meets spec I'm inclined to use it. A lot involved in changing flywheel tooth count. I'll go there when I have to.

I don't think there's enough wear in my crankshaft flange where these bolts mount to be concerned about. As I also previously mentioned, I couldn't get them out (didn't want to wail on them) so I asked the machine shop to punch them for me. I'm pretty sure removing and replacing them once or twice in my lifetime won't wear out anything.

"6 of one and half dozen of the other" makes absolutely no sense? Really?

Thanks for the advice. I'll think I'll stick with tapers for the time being.

[RonD2]

Sometimes this forum reminds me of this other classic:

https://www.youtube.com/watch?v=2A-SOVQvPyg

Probably get a ticket for not putting this in the humor forum.

[wesk]

Whining is not becoming of you Ron.

The reference to your comment "6 of one and a half dozen of the other" was meant to inform you that your current issue with the two choices was not a "6 of one and a half dozen of the other" comparison. Factories do not deliberately spend a lot of money on tooling and parts when the two parts are just as good as the other. They spend the money to tool up and replace a part because it is a financially solid need to do so. Meaning that the old part was UNRELIABLE and they needed a new part to cut down on warranty claims. Try to use your head for a moment here: Tapered studs are forced in to hold two parts tightly so they can not move against each other. Each time you drive them in you remove material from all 3 surfaces. Each time you drive them out you remove material from all 3 surfaces. There are no simple ways or simple tools to measure the fits after several replacements to ensure both studs are retaining the crank and flywheel tightly at both holes. That is why the engineers went to a more closely machined system using very close tolerance shoulder bolts. They are not damaged on each R&R like the tapered studs.

The above 150 word explanation is why we experienced mechanics prefer to offer advice to folks that take the time to carefully read our advice and act appropriately on it. I can only hope you paid better attention this time. I would feel bad if you let a fixed attitude issue cripple your ability to grasp this advice and use it to your advantage.\

Have a wonderful day Troop!

[RonD2]

Thanks for your patience Wes!

Ok, that's the nugget! They switched from tapered to straight dowels because the tapered bolts are UNRELIABLE. I can understand and appreciate that. Although I'm sure it happened to somebody somewhere, all my rookie research so far in this and other forums didn't show one instance of a flywheel (or dowel, bolt, or nut) coming off in operation and causing the catastrophic damage that would obviously result. I agree, even if that failure isn't common, it would only have to happen once to matter.

What I'm struggling to understand is this:

I read and study the manuals like you taught me. The TM9-1804A paragraph 74 (pg. 83) and paragraph 85 (pg. 89) say that drilling the crankshaft flange and flywheel for straight dowel bolts is necessary only when using either a NEW crankshaft or a NEW flywheel. It even says the straight dowel bolts are supplied with the new crankshaft and/or flywheel. The TM says nothing about the change being necessary when using the original crankshaft and flywheel. That tells me that if everything is otherwise serviceable they can be safely used with tapered dowel bolts. Am I reading it wrong?

Did I read this wrong too? http://willysmjeeps.com/v2/modules.php? ... ght=dowell

It seems to me that if this was a reliability (and safety?) issue, then the TM would REQUIRE replacement of all tapered dowels for straight dowels --- without exception. Thinking maybe my manual doesn't have all the changes, I searched for change pages and MWO's and could find nothing making it mandatory. Maybe I missed it?

Assuming my crankshaft and flywheel otherwise pass inspection at the machine shop, I'll ask them the cost to change-over to straight dowels. In for a penny, in for a pound....

[wesk]

I wouldn't do any assuming until I had all the evidence Ron.

You are currently bantering with 71 year old professional mechanic who bought his first jeep in 1972 and has owned more than 10 since and currently own 5. That being said it stand's to reason I have a ton more evidence at my disposal than you do. The bulk of my research from 1972 thru 1995 was the old fashion way buying manuals, joining clubs, the school of hard knocks, calling on an ancient style phone jeep parts dealers and stopping people with jeeps that I saw on the road to ask questions.

So when you ask me what you should do in a certain situation I take that ton of data and in a few short moments I type a couple of sentences to answer your request. Yes they were only a few short sentences and lack a detailed explanation of how they were arrived at. But that detailed explanation of each segment of my advice takes a significant piece of my day. Again I remind you that I am 71 years old. I don't have a lot of days left. So I leave it up to you to do your share of the research when you have the time after you have followed the wise advice and still have the time to enjoy your jeep!

Back to your reply:

The TM says nothing about the change being necessary when using the original crankshaft and flywheel. That tells me that if everything is otherwise serviceable they can be safely used with tapered dowel bolts. Am I reading it wrong?

Wrong. You are making assumptions again. The manual TM 9-1804A is not a user manual. It is an ordnance technicians manual. That manual assumes the person using it is a trained professional Ordnance technician. That trained Ordnance technician would follow the rules and procedures he was taught and learned both at school and on the job. Most Army motor pools seldom rebuilt an engine. They installed a depot rebuilt engine and moved right along. The troubled engine would get crated and shipped to an Army Repair depot where it would be overhauled. That depot would as a routine apply any known factory improvements to this engine during it's rebuild. That includes updating the crank from tapered dowel pins to straight machined dowel bolts. This is a factory update based on the factory's experience with the reliability of the old parts. The Army would not waste money in the field making this improvement unless there was an obvious issue with a worn or loose tapered pin or hole. It does not take a rocket scientist to figure out that each engine overhaul would prove much more cost effective and experience a much longer life spam with the new upgrades that have been developed since the original parts introduction. This is what the Depot would do.

So, why should you follow the same guidelines? Because you only have a 50/50 chance of not having to rework your engine for the upgrades you ignored just a short time after you decided to press on without them. It is always the best approach when rebuilding anything to incorporate as many of the improvement items as possible to prevent an early re-visit and increasing the cost & workload later.

[RonD2]

I much appreciate you taking the time to explain "the rest of the story" --- stuff a 63-year-old rookie wannabe mechanic like me can't get from reading between the lines in a TM. Good stuff, worth its weight in gold!

Yes, I made a note in my TM that the swap is mandatory, and changed my engine overhaul parts buy-list from tapered to straight dowel bolts. I'll ask the machine shop to drill the two holes for me.

I think you can rest easy that by taking the time to type the detailed explanation like you just did --- a good part of your knowledge, experience, and expertise will live on (in this forum and other where) for many years to come!

Thanks again Wes!

[wesk]

But I prefer not to write a book every time Ron's asks what he should do in a particular situation.

[RonD2]

Understood Wes. Your patience is only surpassed by your generosity, knowledge, expertise, and experience! I could be mistaken, but doubt it's just me that benefits when you give extended answers to us boots.

Would you rather I moved in next door?

As for writing a book (of nuggets like the M38 Reference Guide) --- I think it could use a companion volume for the maintenance side of the house. Things you learned the hard way, take for granted, and from those that taught you. Throw in a few sea-stories too. Have you considered it? I'm pretty sure it'd sell like hot cakes! Heck, even if you just cut and paste your photo albums and edit some of these posts down to the technical stuff you'd have a best-seller. Searching through 65,000+ posts from 5,000+ members (including the mis-spelled variations) gets a little challenging......with a book out there you wouldn't have to repeat yourself so much, and us dumb bells would have something to study when you have better things to do....

Without getting mushy, we love you Man! And I kid you not.

[wesk]

Well, Thank you Ron. Appreciate your candor! If you guys shop a wee little bit there are already a few dozen books out there that cover the areas you have mentioned.

https://www.amazon.com/s?k=classic+car+ ... f=sr_adv_b