MACDAD260

Finally got the new motor running tonight. A Gen V 502 Carb. Stock exhaust w/ Corsa Captain's Call. Had the distributor a tooth off but, once I figured that out it started right up. Ran it for 10 minutes at 1500 RPM to start the cam break-in. I monitored all the temps with an infrared temp gun. Everything looks good! I would have ran it more but my garden hose doesn't quite deliver enough water at that RPM to keep it cool. Final water temp was 182*. Also left one of the Y pipe hoses loose so I had a water leak but found it right away, no problem. Next step now is to pull the exhaust and valve covers off and re-torque the heads as advised by the engine builder. I'll do that this weekend.

I am using this engine as an upgrade to the original 7.4L. It ran good but, I wanted more power. I thought about hopping up the stocker but, while discussing this with an engine builder/customer he suggested that I just go with a 502. I said sure that sounds easy but I didn't want to spend that much. He said he knew of a guy that bought warranty take-outs from Mercury and could get me one that was guaranteed rebuildable. It was one of those "I know a guy who knows a guy" deals but I decided to give it a shot as my guy is very well known and respected. He rebuilds a lot of antique marine engines as well as a bunch of circle track stuff and everyuthing in between. You could eat off the floor of his shop. He is a boater, also.This was in November of '01. About the first of February, '02 the motor arrived. I paid $1900 for the 502 long block. Upon dissassembly we found that it had one broken piston and one scuffed. Probably got overheated and detonated. The bore and head were not damaged at all.

The rebuild consisted of 3 used stock size pistons, Hastings ductile iron rings, Clevite "H" series bearings, new lifters, new chain and gears, new oil pump, all cylinders honed to .005 clearance, block decked, heads shaved, rotating assembly balanced, crank polished, bowl port on the heads,(I did that myself) Fel-Pro Marine gaskets, & ARP head bolts. Resused the crank, rods, cam and 5 pistons. The price for this work and parts was $2000. Plus I bought a used flywheel and Performer RPM intake for $50 each.

I am using the stock Weber 750 carb for now as well as the stock oil cooler. I installed a Gaffrig Oil Temp gauge so I can monitor the oil temp to see if I need a larger cooler. I also upgraded the prop from a 21 Mirage to a 24 Bravo 1. My previous top speed was 55 on GPS in a 1993 Baja 260. I am hoping to pick up at least 6-7 mph.

The finall analysis of this project will be an on the water test after I break the motor in for 5-6 hours. The final cost is a little higher than I had planned for (Surprise, Surprise) but I like the fact that I now have a better than new engine for about a grand less than a new crate motor. I also still have the stock 7.4L to put back in the boat when I sell it. I'll still have a 502 to put in the next project or to sell. If I had put money in hopping up the stocker, I doubt if I would see any return on that when I sell the boat.

I did all the swap work myself plus a bunch of small upgrades to the boat while the engine was out. It was a ton of work but, hopfully well worth it. I'll update this post in a few weeks when I get some lake time on the boat.

See ya, Doug

fred

Doug, keep us informed on the improvement that the 502 makes in performance, what rpm were you running with the 21p mirage?.....going to a 24p 4 blade may be too much....but the water test will be the final determining test there, sounds like a good motor to upgrade over your last one.....Fred

Red Stripe

Sounds great Doug!! Congrats on getting it all back together!! Can't wait to see the Baja fly this year

Waterfoul

Hey Doug, if that Bravo 1 turns out to be too much prop for you, don't sell it quickly. I may need it!!!!!!

Wanna race?????

MACDAD260

Hi Fred and Red Stripe,

Hope to see you guys on the water this year. Fred, do you get over to Lake Michigan? I tried a 24 Bravo 1 last fall with the 7.4L in the boat. With the 21 I was turning about 4800-4900 rpm. With the 24 I was turning about 4300 rpm. Same top speed but what a hole shot! Plus it made the boat ride more level in the water. Didn't need the tabs at all in 1-2 footers. If I can turn about 5000 rpm with the 502 I should get the added speed I am looking for. Can't wait to find out.

See ya, Doug

MACDAD260

Hi Mike,

How's your motor coming? It's getting warm. Better hurry up! Did you buy a truck yet?

I think you already know the answer to your last question.

See ya, 502 Doug

tomcat

Sounds like a great deal. Were the crank and rod journals okay? Some of the early 502s had oiling problems. Check the two oil bypass valves in the block. I got my engines the same way you did, and found they only had 11 psi valves not 30 psi. Depending on how you plumb the oil cooler you need to replace both valves with 30 psi or one 30 and remove the other one. This is because the remote oil filter, cooler, lines and fittings create back pressure that tricks the 11 psi bypass valve into opening at higher RPM.

The result is the oil doesn't get filtered or cooled and goes directly back to the engine. After WOT for a few minutes the oil is so hot that you have low pressure when you return to idle. The valves are cheap, but a difficult to change with the engine in the boat. I had to pull mine back out to change them. While you're at it, make sure your oil lines are big enough and don't use 90 degree fittings. This also helps reduce back pressure.

By the way, plumbing the oil cooler in series with the oil filter remote housing allows you to remove the bypass valve in the center hole of the oil filter pad on the engine. This eliminates three 90 degree turns inside the block that are only there to route oil to the oil cooler fitting holes on the block.

Good Luck!

MACDAD260

Hi tomcat,

The crank and rod journals were in good shape. Just a few small scratches that polished out. Used stock size bearings. Clearance were all good. I don't know the exact numbers, though.

I'm glad you brought up the oil bypass valve issue. The motor was delivered without a bypass valve in the intake side of the filter pad (off-center of the threaded part). I just went to the local Chevy dealer and bought what the parts book called for and installed it. How do you tell what the psi is? This one did not take much pressure by hand to open. Where did you get the 30 psi valves? I am concerned about this. I want this engine to last a long time and I am willing to do what it takes to make it right. Are the 30 psi valves a GM part? Do you have a part number for them?

My oil cooler is plumbed in line after the filter. The hoses are number 8 AN. There are 2 45 degree fittings on the cooler, all other fittings are straight. My main concern is that most of the oil is going through the filter and cooler. I have the sending unit for the temp gauge installed in the remote oil filter housing on the opposite end of the intake line. With an infrared temp gun the readings on the filter were consistent with the gauge so I think that location should be OK as long as I am getting good flow from the engine.

Any help regarding your experience will be appreciated.

Thanks, Doug

Mr Gadgets

Macdad260,
Congrats on your new motor.. sounds like a very rewarding project!! I am sure you will have many years of fun with that torque monster.
The oiling issue.. I believe you need at least #10 lines to pass enough oil. That would be 5/8" ID on the line. If you need to make 90's or 45's use the tube type AN fittings. They do not have near as much restriction as the cast and drilled fittings. My feeling on the bypass valve is to plug it, that forces all the oil thru the filter. There are problems with this too. I have heard of filters plugging up and stopping oil flow all together. So the 30psi bypass is at least a must. It has been several years since I worked on the Gen V block, but I did remove one valve and plugged the other. Did a little compressed air on it to decide which way the oil flowed in the block. I believe I removed the one in the center of the pad and plugged the other one.. but dont trust my memory.. cause I dont.. LOL.
With your temp gauge in the filter pad, after the cooler, you can set your sights on a higher temp. I have been trying to find a spot after the cooler to see how much "cool down" the cooler gives.. just havent found one. I would be conservative on the temps untill you get a feel for the motor and get some time on it. I would change out the lines and dont use the block fittings to plumb the the remote filter. Get a remote pad adapter that bolts to the pad on the block. Did you use the one from your previous motor or was it a Gen IV motor? After market units are ok as well as the stock Merc units..
If you have any other questions.. you can email me or post.. I dont know what part numbers are the 30psi bypass valves, but maybe the Hi Perf catalog will tell you. Or have the Chevy dealer call in for the info or Tomcat may have the numbers. Good luck and if you do have to pull the motor out again, to check/change it.. it is not as bad as pulling it out to replace bearings and a crank.. And the second and third and forth times it gets so easy.. believe me I know.. *S*

Dick

HighPriority

Good luck with your new engine, sounds like you did everything the right way.
If you find that the 24 bravo 1 is a little to much I have a very nice 22 bravo 1 that is in new con. and is labbed by Hill props.

Warren
High Priority Offshore