vacuum test results 1991 454

Before I fogged the engines for the winter I took some readings with a new OTC Vacuum gauge and extracted oil from the dipstick.

Port:
15 @ 600 *
17 @ 1000
20 @ 2500 - 3500

Starboard
16 @ 600 **
18 @ 1000
20 @ 2500 - 3500

* needle shake and ruff low idle
** some but less needle shake

When doing the quick acceleration test I drop only to reading of 10 and then up to 25.
At a faster idle about 900-1000 the needle is solid and engines sound good.
I have trouble seeing whats what since I'm new to vacuum testing.
After reviewing link below I wish I had more time to play with timing and mixtures.
I always seem rich but better late then early.
I dont see a flicker at low idles I see more a swing but not 13-17 as the test#15 shows. I only swing 14-16 if that.

http://www.secondchancegarage.com/public/186.cfm

I think I might have a mix of top getting worn, and not being able to get carbs adjusted and timing optimized.

Does anyone know a good machine shop on Long Island NY for my heads? What would be a ball park for rebuilding heads?

With 1290 hours I think it would be a good idea now. I will wait for the Blackstone results before anything, to rule out obvious bottom half issues.


Comments and sugestions welcome.

Thanks,
Scott

Scott,

It ain't Long Island BUt.....Eddies Valve Grinding did my heads in Sayreville, NJ and I don't know how I got lucky but choosing them to do my heads turned out to be an excellent choice. My guess is that they are track enthusiasts and they know performance and other significant elements of head work. He knew all about the Crusader blocks and marine heads. He replaced a few guides and valves, the finished work looked so nice it seemed a crime to bolt it back on and hide the beautiful clean fly cut as well. He tested the valve sealing and flow, and it ran about $475 for both sides on one block. Time was not a critical demand but they were done within 24 hours. This was about 3 years ago and IF I had to do it again...not even a second guess, I'm going back there......AL

kimcrwbr1,

On the hg tests:
If you look at #4 "poor rings" it shows steady at 17 hg. According to the link "normal" #1 is 21 hg. Are boats different?
Also, for the acceleration test I only drop to 10 hg on the low. Is there something to that?

http://www.therangerstation.com/Magazine/Summer2003/VacuumLeaks.htm


On the compression/leakdown:
I think I maybe able to do this even though I fogged? So this test
tells be piston and ring wear? How to tell whats what with cam and crank
and bearings? I hope the blackstone oil test can shed some light.


Thanks,
Scott

Scott,

The oil analysis will be a strong indicator of several things. What got me when I first started is how to discern which comes from what. I can do a more than expected amount of work on my engines but I am not a pro or senior diagnostician. Mine was easy as Blackstone listed a source of where the "contaminents" came from and the antifreeze was the big culprit which I kinda knew anyway. It would be a great luxury to be able to pull these components and mic and measure in the comfort of a warmer space. THAT's why I loved working on vintage motorcycles...I could keep 10 in my garage and still have a giant place to work. My brother had barely enough room for his mustang.

Since you have about 1300 hours, you may find your valves developing issues but clearly not enough to prevent running. If you are near western Long Island, call or stop in that shop in NJ. Eddie is a wealth of knowledge. Can't hurt, in casual discussion you might just find something to help you focus.

Al, I just mailed out the oil samples. I'll ring the shop and talk. I'm in western LI.

I think I should wait until its warmer to gather more information. It sounds possible that I can get another year (or more) with timing and carb tuning, or I'll pull and machine them in march.

PS have a couple damp spots on top deck where outrigers attach that need to be opened cleaned up, filled and reseated before freeze. (thats another post)

Gee Scott,

I became quite proficient at those spots... One thing I did do you might consider ...Since the usual culprit is an owner drilling and not sealing screw holes, I made up hockey pucks from 1 qt wonton soup containers. Filled them chopped fiberglass mat and epoxy and embedded them into the new replaced balsa zone. Now when I replaced the pieces mounted there, the screws went into solid materials...Has held up nicely so far (6 years). If you want any pictures of the repairs, I can email them to you...AL

Scott:

Possible you are seeing more than one issue during your testing. When you go to do the snap throttle WOT test, you really need to get the throttle wide open and do it fast. My experience is the best approach is to unsnap the control cable and open by hand.

Also, the rough idle on a big block (properly tuned and in good mechanical shape) is typically due to a rich mixture. And adjusting the mixture screws usually don't have much control. The fix isn't hard but takes a bit of time to get optimal...just more custom tuning for your specific setup.

Also, the standard production cam in a marine unit will give an idle with a little roughness. also, I find the most useful number from the vacuum test are those taken with the engines under load, at operating temperature...testing at idle won't tell the whole story.

Mark,

makomark said:

Also, the rough idle on a big block (properly tuned and in good mechanical shape) is typically due to a rich mixture. And adjusting the mixture screws usually don't have much control. The fix isn't hard but takes a bit of time to get optimal...just more custom tuning for your specific setup.

Click to expand...

I'm not following you... are you saying mixutre screw is not going to help much? what custom tuning for setup? timing? i'm 8 BTDC at idle with the delco at tune mode. I think you mentioned removing the heads and bring them to a good shop to look them over. i think thats a good idea. with steady vacuum above 900 makes think twice before i pull them though. i'm thinking i could be spending a lot of time with lash. that should be fun though, and i know you guys will get me thought that...

What I'm getting at is most of the time, to get the idle speed up at 650 +/-, you have to open the throttle stop so much that the idle mixture circuit doesn't work. The bulk of the fuel has started flowing from the transfer slots and typically adds too much fuel at idle. The custom tuning refers to rectifying this situation - returns the throttle plates to where the fuel comes from the idle mixture ports and the screws give you fuel control. You can se if this is the case by removing the throttle cables and backing off the throttle stop until the idle goes below 500. If the idle mixture screws then provide their desired function.

The lash isn't hard to do, especially with the engine running. Only drawback is that method can make a mess with the rocker covers off. there's got to be over a dozens posts in this forum on that very topic...time to read some more.

Thanks again Mark. I understand now. I'm looking forward to the spring when I can get to work on this. I was reading how to adjust lash with running engine from the manual I got on this site. Looks like I need the stoppers to avoid the mess (or is that just to minimize it). Looks like winter is time to read...