Compression test?
 

We'll as the title says I had to do my first compression test, today. I warmed up,the engine, disconnected the coil, but I didn't keep,the choke open will,this change the readings? My numbers didn't come back all that great the worst was 105 best 115, now shouldn't a good reading be about 150. This all started at the beginning of the season, boat didn't idle right last top end rpms. I put new cap, rotor and new plugs. When I changed the plugs number 4 plug was bad totally fouled I guess I was running on 7. After that boat ran great, until that same plug fouled out again. Along with that I started to notice I was using a lot more oil I run Mobil 1 15w50 synthetic.
I have already talked to the shop I have dealt with for over 20 years about this and showed him a couple of the plugs, and he said with a smile this doesn't look good. After talking for a bit about different problems this could be I asked what a total rebuild would cost he said about 5k with them taking it out and back in.
The engine was a remained gen IV 454. I have read many other post over the years guess I didn't think this would be my engine. Any thing you have to say good or bad I would like to hear it, I just want the boat ready in the spring

Thanks

Mark

Open throttle would maybe change only 5 on reading... Of course what you don t want is having 45 pounds different from one to the other! Seems like it is not your problem! BUT !

They are low... Since you say its burning much more oil, looks like its time for a rebuild. You could always take a leak down test, this would tell you more where is the problem for low compression. But burning oil tells me cylinder and rings!

Keep us posted!

I was thinking rebuild also, I guess this boating.

with compression being that low and useing oil i would say tired rings,valves not sealing well and valve springs weak.afraid it is time for a rebuild.

How is the compression on #4 vs the others? From your description I was leaning towards number 4 is sucking oil through the intake gasket, from the lifter valley. If it runs good until the #4 plug fouls I would look at the intake gaskets and even the intake itself for a crack.

Well I also forgot to tell you when I was ready to take it out of the water the last time I did notice a couple of small water droplet around the top of the intake not a lot no water in the oil.
I know most of you have more engine experience than I do, if I do a rebuild having my shop do it just keeping it stock does 5 k sound right or is this low.

If you decide to rebuild and are budget minded you might think about one of the head sets for sale in swap shop section. 1 set is oval port 279 heads, that will give you a little higher compression with fresh rebuilt. The other set is 088 rectangular port with 150 hours includes roller rockers. Either of these should save you a bunch of money. I wish these were available 2-3 months ago.
Just thinking out loud.

I would love to throw more power in the boat but I only have the alpha. So I think 350hp would be it.

Same problem with my '87 242. No hole shots and easy on acceleration. I added power this summer and my short term solution is keep a spare alpha drive in suburban, cheap insurance. Longer term solution is bravo conversion when i put real hp to boat. Good deal on new bravo hp complete transom set-up in swap shop $1,500 (i think). Just add an outdrive and you are set for adding substancial hp.
Good luck and keep us posted.

Did you repower or rebuild and hp did you end up with? I have over 300 hours with this alpha and no problems.

Lots of opportunity for a.lucky break till oil consumption and plug fouling join the table.guy.here in Texas has a gen 6 454 cheap with a carb .roller cam better heads ,prob less years of internal erosion ,leave you some money for fresh manifolds serp belt conversion maybe a bravo .yea and keep us posted

http://www.jegs.com/webapp/wcs/store...1&pgGrp=catNav
Bolt on your accessories, make sure it has brass freeze plugs and go boating.
Please don't buy used heads and just bolt them on. You will never get the entire story. I won't even sell heads to someone that doesn't intend on taking them to a machine shop.

Masi242 tried to pm your box is full

Cleared pm

Lilred I would like to just use my parts, heads and have everything redone, I wish this wasn't a budget rebuild but with one in college and one is a senior in high school.

Weather looks good for the river run Sunday you'll be driving the TG.

I copied the link because you said it was looking like about $5,000 to rebuild what you have, which sounds about right. So for a couple hundred more you can have a better package. Then you have a block and some other parts you can sell, be ahead and not be worried in April when the machine shop isn't done lol.
Yes I'm very fortunate that I'll have the top gun on loan for the day :)

+1 w/lilred
while you are waiting to install look for a pos boat w/bravo drive on craigslist and replace that alpha while engine is out and sell alpha and any other goodies from doner boat to recoop investment.
Keep us posted good luck

Thanks Gary nice talking with you

I agree look at other isues before you lay your money cown for a rebuild. First thing I would do is try another gauge as your numbers are consistant. Very unusual for all cylinders to all lose compression. I am usually looking for the spread between highest and lowest as a sign of an issue.

Thanks pantera I was talking to another OSO member and he also suggested doing a leakdown test to double check. So when I do the leakdown I should pull all the plugs and have choke open full. If I am missing something please let me know, I am still learning.

Mark, how many hours on that block sence last rebuild? While you are getting the leak-down kit you might also pick up a new compression tester to verify your 105 reading.. I agree all cyl's showing that low compression and that close is odd.
When it was rebuilt were the stock heads reused? If there was a head replacement that could very well lower the compression across the board, also if a thick head gasket set was used it too will show lower compression.,
having said that, neither addresses your #4 plug fouling problem.
Many here know far more than i about motors but i am guessing a valve train problem on #4
let us know. Good luck and don't let the nuts and bolts scare you, nothing overly complicated in doing top end rebuild in your garage.

We'll I was having trouble finding tdc. For the leakdown, I think I know what to do now. We'll just before it got dark I thought I would try doing the compression again but the engine was cold, but I did open the choke my readings were much better. We'll try again tomorrow .

Mutch better, can you quantify?

Pull the plugs to turn the engine over by hand easier. Use the timing marks to find TDC for number 1 and follow the firing order turning the engine over 90*. Make sure it is on the power stroke. Getting it at the top is the tricky part without a degree wheel. Also, do it on a warm engine.

Compression test should be done with the throttle plate(s) wide open. Just a fyi on 4 stroke outboards if you leave the throttle plate(s) closed you could be surprised how low the #'s turn out. Just saying. I would redo it to see what takes place then move forward from there. Also how well or not does the engine run on the water ? can you achieve max RPM's underload ?

Guys thank for all the help. I just finisher the compression test again
1-130 had some oil around it but not bad
2-125
3-130
4-130. This was the plug that fouled out on me
5-130
6-120
7-130
8-125
Test was done with the engine warm all plugs out choke open.
As I was warming up the engine a little bit of water started to show around the intake in front of the engine. I am headed back out to try the leakdown. I know these numbers are still low, but they are better than before. Let me know what you think.

Thanks

I think your numbers are fine and #4 is sucking oil from somewhere. Should be a cheap fix. Start by pulling the intake and inspecting the gasket where it seals towards the lifter valley in the area of #4. No need to do a leak test on the engine with those comp numbers in my opinion.

Start by checking the torque on the intake manifold bolts. Don't quote me on it, but I seem to remember it being around 35 ft.lbs. If they are substantially loose, Replace the intake gaskets first and see what happens. Your compression numbers are awfully close to each other to really indicate a major problem. It would take something like the timing chain being off a tooth to bring all the numbers down equally, but it wouldn't run for $hit like that.

Two things when doing compression tests:

1) Fresh battery. Cranking speed has everything to do with how high your numbers get.

2) Carburetor / throttle body - wide open. As OP discovered, choke too. No air to the engine, nothing to compress. Note: smaller the cam (less overlap) the more this is important. But...it's super important on everything so always do this no matter what.

Also you will get different readings using brand X compared to brand z compression test gauges. We have seen brand X showing 105 psi compared to 130 psi from brand Z as an example.

Also compression ratio plays a part with the overall compression test #'s. fuel and or any water in the cylinders will always make the compression test #'s higher than what they really are. Also before doing any compression test it is always wise to disable any electric fuel pumps.

mercruiser recommends compression #'s to be a min of 100 psi and no more than 70% different in values from the your highest testing compression number compared to your lowest testing compression number.

Always open all throttle plates, chokes when doing a compression test.

Like I said before I can not post from mercnet but found the same Service bulletin that Merc sends out.

www.boatfix.com/merc/bullet/97/97_25.PDF

Basically the same info as I posted and also performing leakdown testing.

We'll I was only able to number 4 done getting before it got dark. I am not sure if I got it done right but when I put air to it I could hear it coming out of the valve covers. But will i do again. At this point I will check the intake bolts, but I am sure I will,but a new one on.

I do appreciate all,the info this is what makes this a great site.

MASI242, NOW THAT YOU HAVE EXTRA $$ FROM THE ENGINE LEFT THIS ON SWAP SHOP 2 bravo one drives and complete transom assemblys
GARY

when doing the leakdown their are several ways to do it...i use my head and not my body..i install the fitting in the sparkplug hole and with my starter button and my thumb over the compression hose i bump the starter until i feel the compression..then ill put a 1/2'' breaker bat with a 3/4 socket to hold the crank from turning when you induce the air from my leak down gauge..once you induce the air you can turn the crank to minimise the air leaking past the valves,once you find tdc on that cylinder you take your readings..its almost impossible to find tdc on the cylinder your working on unless you either have the harmonic balancer marked from a degree wheel or the rocker covers off to see if both valves are closed..

Or Buy a Top dead center tool they are spring loaded so when the piston hits TDC the ruler marks on the tool are at there highest point as you come off of TDC the ruler marks start to go down, I have them and sell them as well. These are not your piston stop tools either. it is a great tool to have weather you do this for a living or a do it yourselfer. Anyways not trying to sell anyone anything, I mainly sell more these days to marine dealers than to retail customers.

I will give you tips on doing a leakdown as trying to find your leak source. Use Kleenex. Yes Kleenex tissue the lightest ones per tissue- put one over the carb put another one over in place of your oil cap and another one over your dip stick tube (pull the dip stick tube out first) next if you have thru hull exhaust open up your internal flapper completely wide open or your external flapper completely wide open, then tape one corner of the Kleenex over your exhaust tips. Do your leakdown test according to their directions.

If air is leaking past where ever the leak source is, the Kleenex will be blowing around. Anyways this is how I have done it for years to figure out what side the leak source is. . Also a mechanics stethoscope down the oil dip stick tube works also to hear air passing by the rings. If its an exterior head or exterior head gasket leak usually soapy water mix will pick that up as well.

So how is the poroject comming? Leakdown test results?
Gary

Gary I really want to check #4 cylinder did it twice not sure if I got it right but it said about 20% which meant low. Went out will some of the guys from our dock for a run yesterday an they said don't worry, we will pull heads and have them checked at a very good local place and check intake and carb in early spring, just not enough time right now. I guess when the heads come off we will get a good look inside to make sure everything is good. So I guess in the spring I will learn a little more about motors and the $$$ it takes to fix them.

Warm engine?

Yes warm