Inline 6 with high idle problem

[BooBooBoater]

Hi,

I'm back again! My husband and I have been posting over the rebuild of our 1976, 115 hp Mercury Outboard.

Some may remember we put in a high dome piston only to discover a previous owner must have switched to low dome pistons.

So, my husband tore it back down and put in the new low dome piston (#3).

It's back together and running but we have a problem with the idle this time. We took the boat/motor to our local mechanic to get the settings right. He took it out yesterday and set timing, etc....
He said he can't get the idle to come down below 1500 rpm. He's puzzled...he's going to continue working/checking today.:confused:

Any ideas what could have been done wrong during rebuild to have created this problem? It really sounds loud and revs real high....know it could hurt something if we don't figure it out!

Thanks!
Cheri

[H2Onut]

air leak at manifold ?

[BooBooBoater]

We did get new gaskets when we got the piston. However, after first trying to start (after rebuild) it seemed "too tight" and the motor wouldn't turn. So, he had to remove and loosen the piston rods some. When he put it back together, he used the same gaskets and used fresh sealant (since gaskets were still "new").

I hope this isn't the problem...

Cheri

[Pete Keppler]

Something sounds terribly wrong. I rebuilt my IL6 last winter (had the machining done and short block assembled) and when I hit the starter it spun and jumped to life. The engine should not be so tight that it will not turn. The rod bolts and mains should all be torqued to manufacturer’s specs and the ring gaps set correctly. The engine should be free to turn by hand (spark plugs removed). It sounds like your rebuilder messed up.

[Hank W]

you get it figured out. Too much money in it to see it come apart in my opinion. Ask Raceman about it.

[sho305]

Not sure about an air problem as much as the timing/throttle control. When working on a carb problem on my '73 I unhooked the three carbs. I opened them one at a time to see if one was off. It barely made the engine rev as the timing was so retarded at (750-800rpm?) idle. I had to fast idle it to get it to run faster when opening the one carb, so I could be sure it was on the main jet airflow-wise.

I think my '73 Thunderbolt was updated to electronic ignition by '76, but I imagine the curves and timing are close. Possibly the carbs changed and have a much smaller idle airflow and are more sensitive to it, otherwise check the retarded idle timing being correct.

Of course, tend to the above posts so as to not trash anything first!:)

[Raceman]

The possibilities have allready been mentioned: Timing/throttle adjustments off or air leak somewhere. With the powerhead appearing tight at first I'm curious if there was an issue with the dowel pins holding the bearings or reed blocks. The thing that concerns me is the "loosening of the piston rods some". If he in fact loosened the rod bolts, DON'T CRANK THAT ENGINE UNTIL IT COMES BACK DOWN!!!!!!!

I don't think it's possible to overtighten the rod bolts to the point of tightening the rotating assembly. If so, something was likely stressed to the point of failure. If the bolts were randomly loosened and the assembly freed up there's a major problem that could result in catastrophic powerhead failure.

At the risk of telling you something you already know, the engine's RPM's are increased past the point you're talking about by timing advance. At 1500 RPM's, the carbs haven't begun to open if all the pickups are properly adjusted. One or more of the carbs opening at this point could make the idle too fast, but would make the boat real lazy down low, to the point of probably not getting on top.

REAL CONCERNED ABOUT THOSE ROD BOLTS.

[CrayzKirk]

Hi,

I agree! It should turn free and easy with NO binding or stiffness. I was working on my older inline ('66 1100SS) last weekend and when I lift the cold start lever, all it does is advance the ignition. The engine runs much faster in that situation. It sounds like the timing belt is on wrong (if it has one), the throttle linkage is off on the trigger or the trigger is binding and stuck advanced. I put together a crankshaft, rod combination last week and one of the rods had a slight catch in it. Took it apart and one of the needles was askew. Did you tear it down all the way? Replace the crankpin bearings? I'm not sure, however it looks like the cages match up only one way and could cause binding if installed incorrectly. Loosening a rod bolt sounds like a good way to throw a rod, trash the crankshaft and block.

Kirk

[sho305]

I agree totally with the rod thing. My point was if the timing is correctly retarded at idle, and air/throttle problem would not make it rev. I have also never fired a motor without running a timing light on the starter first.

Never, ever, ever put a motor to use without making your rebuild job as perfect as you can. I have worked on auto engines in bottom ends, but are there not torque values for the rods and such on this? My manual is up north with my boat.

[kspradling]

Hi,

Yeah, the torque values are as follows:

180 inch-pounds done in three steps:

60, 120 and finally 180. Or 5, 10, and 15 foot-pounds if your wrench doesn't measure inch-pounds. I would recommend one that does because it is much more accurate at low torque settings.

Check for binding after each torque step of both nuts/bolts. You may want to use a bit of red hitemp loctite on them as well. Also, if it is binding, make sure you have the end caps on correctly and on the correct rod. There is a mark that lines up only one way. On my 1350, the casting number on the rods is facing towards the #1 cylinder (up) as well. If you are putting the pistons in first and then the crankshaft, it gets a bit tricky if you have the nut and bolt combination.

As was also stated, make sure the bearing and reed cage locating pins are seated fully and not causing a binding situation. It MUST turn freely by hand with no stiffness, catches or binding.

Kirk

[Raceman]

The engine will actually run faster with the carbs open slightly and no timing advance, but it'll be lazy and build the RPM's slowly, bordering on boggin'. In neutral, it'd be easy to exceed 1500 RPM's with JUST carbs. It's fairly easy to prove this by grabbing the bottom carb and twisting it a little. Of course if the engine is set up right it's impossible to not get timing first. A couple of people on this board who also have a lot of inline experience disagree with me on this, but I've always set my 1500's up to get max timing BEFORE the carbs ever begin to crack and feel that the engines are more responsive this way.

[BooBooBoater]

Thanks everyone for taking the time to respond. First, I better clear up the "stiffness" problem. My husband explained it to me in a little more detail. After he tore it back down, he used a lobster pick to try and rotate all the squirrel cages while the rods were still connected to the crank. He could turn them all execpt #4 and #6. He feels sure that one of the bearings was askew in each.

Took them apart, cleaned and made sure there were no nicks in the bearings. He put it back together. They all turned fine by hand. When he had it completely back together, it cranked fine and fired up after a few tries.

Still don't know why the high idle, but he suspects it's related to the timing also. When the #1 piston came up top-dead-center, the distributor was able to turn one tooth either way, so this could be his problem. He said he did it according to specs. by lining the arrow on the pulley with the three dots on the flywheel.

Still puzzled:confused:

Cheri

[Clams Canino]

Ya - I followed this one along since before the "great hi-dome fiasco". He had to tear it back down because he had a rod or two binding after he changed the piston over to low dome. He never started it that way (binding) - nor did he "loosen" the rod bolts to free it - he dismantled the offending journals and re-assembled
them sans the binding.

Taking it on faith that the block is correctly put together:

The carbs should be pretty much be dead nuts closed at idle, open a little will make it go too fast.

From there check for an advance issue - belt or adjustment.


Lastly: the air-leak theory - though with Chaz's experience coupled with the fact that those things mate so cleanly, I doubt he'd introduce an air leak

It's gotta be something fairly simple, Cod willing.

-W

[Clams Canino]

I'm gonna add my name to a "limited" dissagreement.

In the case of a race motor (with a binary state either IDLE or WOT) I totally agree with your setup.


However, on a fish & ski motor that operates in shades of grey in the throttle department. I tried your setup 1st and find that it runs a bit dry in the lower RPM ranges with lots of advance and decent RPM's but very little mix coming in via the carbs. Maybe I did something wrong, but in my style of use I didn't find that set-up to be advantagious. Were I to constantly pass THROUGH that range to WOT - then I'd do it like you and get the better responce on the hole shot. It scares me in the low/midrange though. I went back to the "book" method.

-W


Originally posted by Raceman

A couple of people on this board who also have a lot of inline experience disagree with me on this, but I've always set my 1500's up to get max timing BEFORE the carbs ever begin to crack and feel that the engines are more responsive this way. [/B]

[stan merck]

Raceman I would just like to say that you were right about the old 135's having the same block as the old style 115. I guess I was thinking of the later style blocks that have smaller ports. They are not as small as the 90 hp though, I have only been into one of them and the ports are so small I dont see how they run as good as they do. I have seen a new style bolt pattern adi ign block with ports the same size as a 140 or 150 but didnt have the power port, I guess that makes it a 115? Some of these blocks {115} do have smaller ports. Anyway I think this guys high idle problem is probably the timing belt being one tooth off.

[Clams Canino]

I can't speak to 1985.

But I can tell you that the 1984 115 (ADI) has the smaller (115) style porting and no power port, while 86,87,88 have the big (1500 type) block porting and power porting. They acieve slightly less WOT hp in these last 115's by giving 1.3 and 5 the 10 reed petals and shorting 2,4 and 6, to 8 reed petals.

Apparantly this was the result of the change to propshaft rated HP and they couldn't bring themselves to "give away" a little extra HP - so they slightly hobbled 3 cylinders.

I don't know if the change came in late 84, or 85, or was new for 86.

We won't know till someone scatters a 1985.

-W

[stan merck]

1982 IS WHEN MERC WENT TO PROP RATING. THE 140 DROPPED OUT OF THE LINE, IT BECAME THE 115. I HAVE SEEN INSIDE 1982 AND 1983 115, BIG PORTS AND POWER PORT.

[Clams Canino]

I just cracked an '84 4 weeks ago - small ports - no power port.

????????????

-W (yes I check the block numbers)