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Old 06-13-2005, 11:05 PM   #15
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I did the 502 replacement in my '74 Argosy 24' about three years ago. The original 454 grenaded, leaving me little choice.

At that time the 502 was going for about $5000. Parts and labor to R&R totaled $2700 including trans rebuild, radiator recore, and a few needed odds and ends like new starter.

I've since added Howell port fuel injection and Banks exhaust for an additional large chunk of money, but the results are excellent. I tow about a 5-6000# race trailer and it does a great job. Last trip I averaged just under 8 mpg at 70 mph, pretty good considering that I used to get 11 with a Ford E350 TurboDiesel van towing the same trailer at the same speed.

As to towing that size load, I have no problems because my 24' has a very short frame extension welded on the back. There's lots of steel in the extension, and I check the integrity of the welds every few trips. Longer motorhomes with longer frame extensions are a different story. For those I'd probably stick close to the factory towing recommendations.

One recommendation: I have had further problems with my transmission. The torque converter apparently came apart and welded itself to the input shaft, trashing the whole transmission (the shop literally couldn't get it apart). I'm now using an Allison-type converter. As I understand it, the internals of this converter are brazed together, where the lighter-duty units use less-robust construction. So far, so good.

Bob
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Old 06-13-2005, 11:18 PM   #16
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One more 502 engine item: the oil cooler plumbing will have to be changed. The original 454 used a cooler adapter that won't fit on the newer engines. The 502 actually has connections built in for the oil cooler lines - there are two pipe plugs near the oil filter mount.

Here's an article I found about using these ports:

Tech Tip: "Oil Filter & Oil Cooler Bypass Valves"
Speed Reading by Wade Hajek of GM Performance Parts

"Gen V and Gen VI big-block crate engines come with two oil pressure bypass valves installed in the engine blocks. Both of these valves are rated at 11 psi pressure differential. One valve is for the oil filter and the other is for the production oil cooler. If you install an aftermarket oil cooler or remote oil filter that attaches to the oil filter pad on the engine block, you should be aware that you need to change the oil filter bypass valve in the engine block. The aftermarket oil lines add resistance which will cause the bypass valve to bypass the aftermarket oil cooler and/or oil filter all the time.

Obviously, if the cooler and filter are bypassed the oil will be dirty and hot. Your engine could run hotter and could be damaged by dirt in the oil. If you choose to use an aftermarket cooler or remote oil filter that attaches to the pad, you should change the bypass valve to one with a higher differential pressure rating. A good choice would be GM# 25161284 which is rated at 30 psi. Remove the valve that is closest to the crankshaft and replace it with the new valve. Press the new valve into the engine block and stake it in three places. You should note that the bypass valves don't need to be changed if you use a production oil cooler which uses the production holes in the engine block and you don't use a remote oil filter. Also, if you use an adapter that just angles the filter for clearance you don't need to change the bypass valves."

The replacement bypass valve can be bought from the GM Performance Parts Catalog through GM dealers.

Bob
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Old 06-15-2005, 08:58 PM   #17
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I checked with my local Chevy dealer today about replacing my 454 with a 502 and they wouldn't even touch it. Said it's too hard to remove the engine on an airstream and even if they could get it out without taking exterior panels off, putting the 502 in would void the warranty. I think these guys are either stupid or lazy or both.
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Old 06-16-2005, 08:46 AM   #18
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A little more Hx

The previous owners of my Argosy stated that they purchased it from a family of a man who had alzheimers and the Hx was not clear. They did know that the engine had been replaced but did not have any paperwork or know the approx. time. The people I purchased it from stated their mechanic thought it to be under 10k miles due to the motor being so clean. It was not a steam clean job. Even today the motor looks new with very little dirt or grime on it. It will be nice to have a "worry free" MH after done. But for around $8000.00 I should have that piece of mind. Thanks for all the posts you have made this a little easier to swallow. I will keep you updated. Thanks again. John

P.S. the local Workhorse dealer / shop will only put crate engines in any MH they work on. Had way too many probs with rebuilds and getting stuck with labor x2 and unhappy cust. Just some advice. Also I am putting all new oil / tranny coolers on and taking factory AC unit out.
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Old 07-02-2005, 11:38 PM   #19
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wtrdawg:

How is your project comming? Have been on pins and needles waiting to hear!

Bob
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Old 07-03-2005, 11:29 AM   #20
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the saving grace is you are putting money into a real Classic that will hopefully keep appreciating in the market as more and more folks realize they are out there, and your own enjoyment will be so much increased.
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Old 07-03-2005, 02:01 PM   #21
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John, what are your plans for exhaust? As the big blocks are notorious for leaks around the ex. manifolds at both the block and the donut ends I've used Headman ceramic coated headers on both my previous P30 and now the new A/S. Just got the unit out of the shop Friday night after header install. It's actually quieter now than when I got it with the donuts leaking.

The heat dissipation of these headers is great. Cooler doghouse temps. More power. Bit better fuel economy. $269 from Summit Racing.
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Old 07-06-2005, 07:16 AM   #22
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502 ugrade update

Well it's been 1 month and as of last week still not done. The problem was finding a 502 since GM back ordered the one I ordered. Found one in CA. Arrived my mechanic last Thurs. and with the holiday weekend I should have it back by the end of this week. I sure hope so. As for the exhaust I am going to talk with my mechanic and see what came off mine and make a decision then. As soon as I get any info I will pass it on. Thanks for your support.

John
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Old 07-28-2005, 03:27 PM   #23
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I have been waiting with baited breath to hear how this upgrade turned out.

Do you have any news for us?
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Old 08-01-2005, 04:52 PM   #24
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Upgrade progress

Well what are we now 10 weeks into this and I have to report this has been a very emotionally draining experience. I got my R.V. back 2 weeks ago and am now on my third return trip to another shop in town to deal with a vapor locking problem. My original instal mechanic returned it to me with a dieseling problem and stated I needed to run the 87 octane gas out then he would adjust and set the timing. Well if his performance on the original install was any indication, I took it to another shop. This shop in town is the Workhorse dealer and they said I needed a new carb and my timing reset. Done and ran great just a little pinging from the low octane but otherwise ran great. Now when the temps outside are around 95 the engine is running around 180 or so and after starting cold and running down the interstate for around 20 minutes I stall and die. Let it cool for a while and starts up and runs good till the engine temp goes above 180 or so. I had the original 195 thermostat changed to a 165 on the dealers recommendation, and it still runs too hot. Kinda like my temper when I died with 4 adults and 3 small children on the side of the interstate. But anyway, I took it back into the dealer and they are now heat shielding the exhaust and the fuel lines. I don't know what else to do but I am tired of feeling like I am being shined on by these so called professionals. They sure have fun playing with my wallet. So far I am $8800.00 and 10 weeks without my MH. I would advise that if you are doing this, make sure you know your shop and you set deadlines for the rig to be done or they will drag their feet and not get it done. My mechanic kept giving me excuses when he had the motor in his shop for 2 weeks. It is a major undertaking and I think he bit off more than he could chew. My bad. However, as for performance, 60-65mph while turning 2600-2700 rpm. not bad and a noticable improvement of power. I will be able to report more once the vapor locking issue is resolved. If anyone has any suggestions please let me know. Thanks....John

P.S. They replaced the carb with a Holley and an adapter plate that raised the air cleaner so high you can barely get the filter in. I hope it all works out so I can give a positive recommendation. AAARRRRGGG!
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Old 08-02-2005, 07:11 AM   #25
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$$$$$$$

John:

Thanks so much for sharing your engine change-out adventure with us.

This is a theme very near and dear to all of us who own antique or near antique Motor Homes – it (the “change of engine”) is not a question of “IF”, only “WHEN”.

Most of us have discussed and have anguished about what to do when our own beasties do exactly what yours did in the Rhubarb. There are many emotional choices to be made when a power plant suddenly has to be replaced. Having thought out alternatives early on enables a clear rational decision on what to do about the engine and jewelry much easier. A good approximation of total cost involved is important in this assessment, and your sharing the actual figures is appreciated.

It’s good to have a plan up front prior to the actual demise of the engine. I think you made an excellent choice with the crate 502 truck/motorhome version of the big block Chevy engine. As hard as it is to part with an additional couple of grand (or more) during this time is still makes sense to change out ALL of the peripherals (carb, starter, distributor, alternator, wiring, belts, pumps, etc.) while the engine is out – everything has to come off anyway – no additional labor charge to refresh everything under the doghouse.

On your run 20 minutes and die problem – a common problem with the longer Airstreams is the fuel feed from the tank to the engine. A cheap fix to try would be to install an in-line electric fuel pump close to the tank – a fuel pressure gauge to monitor pressure just as the gasoline enters the carb may also be beneficial in diagnosing the problem.

It could also be electric – in the past I have driven several cars in which some portion of the ignition system was “temperature sensitive” for whatever reason.

Good luck and thanks again for sharing your costings. Be sure to let the Forum know the outcome of the troubleshooting and your pinging problem….
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Old 08-02-2005, 08:09 AM   #26
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If I were putting in a new engine I would most definitely look into putting at least a throttle body injection onto the new engine. This will take care of any fuel vapor lock problems on your motor homes. It will also compensate for running at low/high altitudes. They system I have is made by customefis.com. Howell is also supposed to make a good system. Do a google search and you will find many vendors where you can purchase an off the shelf bolt-on unit. I actually have a GM throttle body on an AMC engine. All of my carb problems are gone and it runs like a modern automobile. It took about a weekend to install and I was back on the road. I would definitely loose the carburetor if I had the choice.
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Old 08-02-2005, 08:35 AM   #27
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Question Down with carbs!

I must agree fully with Crispyboy in post #26. Modern upgrades to cars, trucks, motor homes etc… should include fuel injection. The carburetor is “state of the art 1960” . Even lawn mowers have fuel injection these days. The “computer” scares a lot of folks but it should not! As does 65-90 pounds of fuel pressure compared to 7-9 pounds. When I was a kid most cars were carbureted and they sucked , get in the car in the winter and begin the pumping of the gas until life would begin under the hood, keep nursing the throttle until the thing warmed up and so on. Heat was another issue all together. Now we expect “everything” from our automobiles – start every time, never overheat, get good mileage, etc… - this has all been made possible by the computer controlled fuel injection. For around $2000-$3000 a nice fuel injection system can be had complete. Most will integrate with a lap top computer for tuning. Additionally, the Edelbrock Pro Flo system is designed to work off of a stand alone terminal, thus no lap top is required for this system. I have had excellent luck with the Edelbrock kit on a 454 Chevrolet and if you PM me I will happily share more. I do not work at, nor am I affiliated with, Edelbrock Corp.



Regards,

Henry



PS: OK you old timers – this was not intended to be a carburetor bashing session. I used Holley’s for years with relative success – but you cannot beat the fuel injection for reliability or smoothness and I think that this is the goal of the engine replacement project.
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Old 08-02-2005, 09:24 AM   #28
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87MH, you brought to mind a similar problem I had in my '78 Suburban 454. Brand new it had a problem that was heat related. Dealer "fixed it" and I proceeded on my way to Florida.... the longest trip. It was fine all the way from London Ontartio to the Atlanta area. As we got into more heat it would just die as I drove along. Cool down go till it heated up again. Had lots of folks scratch their heads as I was running later and later.
Finally made it to Ft. Lauderdale and a friend told me of his mechanic.... forget the dealers and warranty I just wanted my new truck to run.
What he found was an over tightened ignition module in the distributor. If you overtighten you can crack the contact point. When it heats up the crack becomes wide enough to break the connection. It was an easy fix to a very exasperating problem.
So the question that begs to be asked, "do you really think it's fuel or are us loosing ignition?"
Let us know what solves the problem please.... we all learn from these things.
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