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I have a 93 gmc with the 6.5L I found cracks on the #2 main bearing onthe block side. has anyone had this trouble too? My truck has just over 100,000 miles. Where can I find a new short or long block at a good price? Thanks
 

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Avant Salvage has a big diesel shop that sells core's and rebuilt HP motors
 

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due to lack of available blocks replacement blocks, I had mine repaired and had the splayed main cap mod done (talk to John Kennedy or Diesel Auto Services). No problems so far! (guesstimate 2 years??)
 

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The splayed main caps is not just for small GM's, it's for any motor. It will not weaken the block, unless done wrong somehow. I have not read of anyone having a splayed main cap fail. Where have you seen this or read about it?


Avant salvage, the place I mentioned has a massive rebuild facility that rebuilds all diesel motors, not just a guy slapping junk yard parts together.
 

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Well, to each his own, but I was to my knowledge one of the first to set up the splayed mains. I have never heard of a failure of one of the splayed main blocks. In terms of cracking, the stock blocks crack in the main web area, and up into the cylinder bores, NOT out in the pan rail. So, if the splayed main fix moves stress away from the area that we KNOW cracks all the time, it cant be a bad thing IMHO.





I would agree Avant has a good rep overall.
 

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Yeah, the block looks devoid of meat all right






By shifting the load off of the web itself and to the base of the web near the block skirt, we tie the block together with much more rigidity. The cracks that you found were likely at the outer main bolt holes where the stress is high, and the web is weakest...
 

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on a 6.5. Best blocks are the latest AM General versions.


I just had my 6.5 engine replaced..How is it you tell if you have the latest, as they claim it to be?


What block number and where do you look?


Thanks..
 

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My a/c compressor locked up and right after I replaced it the harmonic pulley lost its' polyureathane and started slipping. This also happened to a friends 6.5 in the same order of failure.
 

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Why not use a gear timing set? I don't want to hear a friend of a friend of my third cousin once knew an engineer who said X... I would like some quantifiable evidence from several reputable sources that it causes damage to our engines. Not even that - just show me a repeatable test with data, and describe your testing methodology (hopefully without emoticons). Then, if true, shouldn't you present this evidence and/or start a class action suit against the manufacturer? I am sure there have been plenty of gear drives sold, so you shouldn't have any problems tracking down victims.
 

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Show me the correlation between crank failures and gear drives using something other than anecdotal evidence. Citing people from the diesel page may appeal to some, but doesn't really support your case in my opinion.


If you are convinced that gear drives break cranks, and you can properly support that claim, then I think you have a duty to 1) present that evidence to the diesel community and 2) go after the manufacturers/suppliers providing the defective product.
 

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There is no reason to get defensive over a couple of questions. I basically want to look at the data you have and make a decision for myself. Over the years, I have researched gear drives for the 6.5 diesel and have found a few people on the net trying their hardest to stop people from buying the gear drive solution. These people present similar arguments to yours, but don't offer any real evidence, statistics or testing information. I only see anecdotal observations and attacks upon certain individuals and the products they offer or support - splayed caps being an example.


So, I am giving you a great opportunity to present the information you have. Show me those links to the articles on crank failure and how the gear drive is directly responsible. I just don't see how anyone can say without a doubt that gear drives are causing crank failures without capturing at least:
<UL>
<LI>Number of gear drives in service (miles driven and years in service)</LI>
<LI>Total number of crank failures within gear drive population</LI>
<LI>Total number of crank failures without gear drives </LI>
<LI>Condition of crank pulley and/or harmonic dampner in failed crank engines.</LI>[/list]


With this information you should be able to determine through statistical analysis if there is a correlation between crank failures and gear drives.


BTW, I am not pushing any products and do not represent any manufacturers or suppliers. Actually, I find it humorous that you think I do. If I happened to be pushing products, especially a questionable one, I don't think I would be so vigorous in trying to uncover the truth.
 

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to quote your favorite vendor "I have nothing to prove to anyone"

and my data is just that MY data, no need ot share it with you.

I stated facts and as you know many others agree and have evidence of their own.

as far the the links to the info on thedieselpage that site edits out that stuff quickly so they can keep peddling those products.

here are some topics i found in a quick search about gear drive harmonics and problems.

http://www.lonestarstangs.com/forum/showthread.php?s=5cfc4971faeb35d19842d57945f9075e&threadid=116

http://secondstreetspeed.com/articles/purpose bb part 1/purpose_built_bullet-p1.htm

http://www.automotiveforums.com/vbulletin/t58979.html

http://www.centuryperformance.com/forum/topic.asp?TOPIC_ID=77

http://www.eng-tips.com/gviewthread.cfm/lev2/6/lev3/35/pid/71/qid/61703

the 6.5 harmonc balancer is a weak link to begin with and fails prematurely, so adding unwanted harmonics only quickens that process, doesn't take much smarts to figure that out :p and a bad balncer can result in a broken crank, so again not much smarts needed to realize that. :p
 

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Diesel Pro,


As I was writing my long winded dissertation you were writing yours, Still no quantitative data only more opinion both pro and con.


1st string at lonestar minimal profile for experience plus new to the site that day did not like them no explanation why.


2nd was talk about cars using nitrous and hard core race machines no quanitative negative or positive on gears but said belts were best to minimize harmonics, agree but not practical for the 6.5


3rd string another newbie & limited profile did not like them but no explanation of why


At century performance ADMIN obviously did not like them.


At last one engine tips; it went both ways pro and con but most interesting was this from a NHRA person http://www.nhra.com/dragster/1999/issue16/speed.html look for this paragraph:


One school of thought contends that a gear drive transmits undesirable crankshaft harmonics to the valvetrain. I tend to discount this theory. With the high-strength materials now being used in cam cores and the increase in the size of the camshaft journals, I think the effects of crankshaft torsional vibrations on valvetrain stability are almost nonexistent if you use an adequate torsional damper.


I look at profiles, some don't want to add personal info, or it could all be made up but looking at experience lends to credibility of posters ability.


From what you have offered thus far for me, is still in realm of opinion not fact, BTW I think the gear equipped power project truck at D page has 220K since install on those gears.


On the issue of gears vs chain; replacing with either over an old worn chain will show marked gains. A hi quality chain should give overhaul to overhaul service, maybe more stretch in it's latter days or when putting a high power demand on it, you would not have that with gears.


But I don't think there is enough data out there that says the gears in themselves cause failure. If they were really problem inducers, the liability to repair gear caused damage I'm fairly confident would cause them to be pulled off the shelf.


Those broken gear drive cranks you know of, that happen on Joe Average drivers truck, or somebody hammering the mess out of the truck, in that scenario a chain could do the same thing was the damper bad as well, chicken or egg scenario there.


Harmonic damper fails are somewhat common but you forgot to add that oil on the rubber insert makes it happen at higher frequency rate. Recommendation I've seen even chain equipped, is check at every oil change if you don't have cracks in the rubber you are good to go, but 100K is a good time to change, what are your thoughts on that one.


Edited by: Turbine Doc
 

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Harmonics hey,


Harmonics seems like a measurable factor. I would think the right scope could capture a 2D + time picture of a geardrive's harmonic signature. disharmonics, or incongrous waves would be visable markers. After having replaced one harmonic pulley for another GM one, I would like to hear if there are other manufactures making harmonic pulleys for the 6.5.


-------------------------------------------------------------------


'93 L65 '94L65 EFI '96 L65
 

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QM,


I exchanged an email with a guy from Fluidampr and he indicated they may entering the performance diesel market. I posted a feeler earlier, but didn't get any responses. I think a modern racing HD would be a great addition to the market.


TD,


I think you hit the nail on the head. I am genuinely interested if this is an issue or not. HD/pulley failures are documented, but the contribution of the gear drive to the failure is not. I have read a lot of articles discussing the pros and cons of gear drives, and two things are evident. First, very little info has been produced specifically on the 6.5 and gear drives. The articles I have found have been mostly positive. Second, gear drives destroying a crankshaft, either diesel or gas applications, typically isn't listed as an issue.


I should have identified the pattern earlier.
 

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QM,


If you got the time and equipment you could do that, but I bet it's already been studied by gear mfrs designers/engineering team. One thing I've found over the years dealing with Engineers they tend to go conservative for the long haul, which is why we can be so successful in unleashing the extra potential of the 6.5 if done smartly. Corporations design for and give extra margin for longest avg. service life.


In todays ever litigation happy world, if imminent failure were result tied to a defective product install, somebody would own that company or they would fold. There was a extensive test and monitoring of a gear install at D page, as above I think that is now a 220K install, no problems have been caused, many others are running and report good results.


Notable to the 220K one is that it has been periodically pulled down and inspected no adverse wear or stress reported, photos and written articles for all to read are available, while not a scientific disertation or detailed Engineering investigation, one can read and see very thourough thought has been given to a "real world" test of the product in use.


Help, anybody know how to use spell check on this forum, I ain't dumb, and recognize typos but get tired trying to undo and edit mistakes attributable to my poor typing skills, or thinking faster than I can type.
Edited by: PostModerator
 

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TD,


This was the kind of discussion I was hoping to get. I agree with your assessment on engineers and the products they market. In addition, I too have read the DP project updates that confirm my initial thoughts on the subject. Granted, it wasn't the purely scientific data I was requesting from DieselPro, but I think that if you are out to discredit a product or manufatcurer, you better have convincing data.
 

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Any "harmonics" generated will come from the crank and if a gear drive passes them on to the cam, it sure is taking it well, because the same gear train up top drives the pump...





The elastomer in harmonic balancers fail from heat, oil, hydrocarbons and ozone as well as vibration. The crank pulley is dampened because the crank "harmonics" can be hard on belts.





To believe that a gear drive hurts the crank is ridiculous... Edited by: Kennedy
 

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I have been thinking about what TD said earlier about how the engineers would have tested the harmonics of the gear driveset.


My point is this:


I have little faith in what I havn't seen for myself. I would imagine that the gear drive set is cnc machined to strict tolerences, but this means nothing when speaking of harmonics. Harmonic tuning would require testing every set for it's sinewave and determining what was exceptable. not every violin is a strataverious.
 

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Where did you see it? That would help
 
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