F100 engine siezed?

[Yamajoe]

A friends F100 started to make sickening noise after running at WOT for about 15min, he managed to get back to dock at low idle; this was about a week ago. yesterday a leakdown test shows good readings for cyl 1,2 and 4. #3 is leaking air out of #4 sparkplug. the motor appears to be seizing as it is difficult to turn flywheel.What could the problem be?

 

[bman1bpm]

Re: F100 engine siezed?

Did it overheat?
Could also be alot of carbon on the rings causing them to stick.

 

[Dhadley]

Re: F100 engine siezed?

Do you mean it's leaking air out the exhaust (not spark plug hole) on the leakdown test? If it's difficult to turn in the entire 360* range, it's most likely something to do with the pistons, bearings, crank or lower unit. But lower units have nothing to do with leakdown.

 

[Yamajoe]

Re: F100 engine siezed?

No the motor never over heated; air was coming from #4 spark plug hole, i will check the exhaust air exit if any today, and start with dropping the lower unit just to discount a possible cause there.Thanks for your advice guys.

 

[James R]

Re: F100 engine siezed?

Your problem may be related to your leaking cylinder but you may have more than one problem.
Try to eliminate the turning over problem. Remove the lower unit to eliminate that. If the motor is still stiff shoot some marvel mystery oil down the bad cylinder plug hole. Let it soak a while and then try turning the motor over by hand. If it has improved then your problem is probably with that cylinder. If a cylinder is not sealed it is possible for the lubrication to fail.
The leak will have to be corrected to check the compression on the bad one.
The comp' check will tell the story.

 

[rodbolt]

Re: F100 engine siezed?

toss the compression tester in the creek and stick with the leakdown test.
good advice to remove the gearcase and retest can the engine with spark plugs out rotate smoothly.
remember the cams are still dragging so some jerkiness may be observed.
only two ways I can think of to have air from #3 blow out of number 4, either a head gasket is leaking or a valve is stuck open or burned.
try testing with the trottles open and the airbox removed.
leakage back into the intake will indicate a leaking intake,between two adjacent cylinders indicates a leaking head gasket and leakage from the ehaust indicates an exhaust valve leak.
a compression test is nice, on that engine a leakdown test is way more accurate and faster to perform than a leakdown test.
placing oil in a cylinder wont affect a leakdown test at all.
basically what a leakdown test is.
we place a known regulated air pressure in a cylinder at TDC both valves closed.
a sealed cylinder.
then we measure how much makeup air does it take to maintain the known regulated air pressure inside said sealed cylinder.
on a perfect cylinder no make up would be required and a leakage rate of 0% would be observed.
however we have ring gaps and hone marks so 3-10% is normal with anything over 15% leakage being abnormal.
but as I have air under pressure on said sealed cylinder if it does leak I can now track down where is the leaking air going.
not but so many ways air can escape said sealed cylinder.

 

[Yamajoe]

Re: F100 engine siezed?

Removed lower unit no change; followed Rodbolt's advise on the leak down test and had air exiting exhaust from #3. decided to remove cyl head, both valves on #2 and #3 were white (over heatedi say); the stiffness in flywheel still remained ( can only turn the flywheel using a large shifter and a lot of effort) so i lifted the powerhead off and removed crankcase;

What i have found so far is as follows: The cyl head is not warped, cracked and no obvious sign of water breach; i have sent this off to the experts; found #1 big end bearing worn so badly it was wafer thin; all piston pins have stiffened not alowing any free movement of the piston but no wear, damaged on the pistons, the cylinder bores have not scuffed or obvious signs of damage, i say the motor was probably minutes from major damage;

I have yet to check oil pump, i am suspecting it may have failed as the there was hardly any oil in the valve train, bore and crank case, although this is a hunch i am still trying to find the cause.

 

[rodbolt]

Re: F100 engine siezed?

last 4cyl F motor I priced out its cheaper to buy a reman or a new block assy than attempting an overhaul.
no undersize bearings are availible so no crank grinding allowed, if a journal surface is bad the crank is scrap iron.
last I priced the pistons were not avalible without rods but that may have changed.
bearing selection is tricky and time consuming to double check all clearences with plastigage.
its mandatory to remove the midsection to access the oil sump and oil sump cleaning is mandatory as is checking the plastic pick up strainer for warpage.
labor estimate for rebuilding an F115 is roughly 40 hours without salt or outside labor for head work or boring.
we dont reuse headbolts,rodbolts or crankshaft main bearing bolts.
basically any angle torque bolt.
the F motors wont tolerate much deviation from correct overhaul procedures and if not followed they tend to die quickly again.

 

[Yamajoe]

Re: F100 engine siezed?

Not good news at all.

What do i get when i order a complete block assembly? thanks for your help.

 

[parrfive]

Re: F100 engine siezed?

Rodbolt quick question if you don?t mind. I tore down a F100 last week and so far ive talked to a master tech that works at another dealership in town. Also have called tech line and talked to my service rep and cant get an answer to my question. The beg end rod bearing and the rod itself have no locators to keep the big end bearings from rotating with the crank. Inside all the rods and the bearings are smooth. Partsmart shows indentions in the bearings but there not there. What do you think?

 

[parrfive]

Re: F100 engine siezed?

Sorry F 100 TLRZ

 

[AGENT 37]

Re: F100 engine siezed?

I have had two four-stroke crank shafts returned to service by sending them to a guy named David in California for repair. He adds metal to the damaged surface, normalizes the metal, and takes it back down to original specs. The cranks have come back looking bran-new and performed flawlessly for hundreds of hours so far. And I paid a fraction of what it would have cost to buy a new replacement. You can find the business and info at marinecrankshaft.com. The process takes a while to do correctly so you need to be patient.

 

[rodbolt]

Re: F100 engine siezed?

parrfive
dunno. lots of funny unexplained stuff was happening back when the 4 strokes were first appearing.
still a lot we get to learn in the field that Yamaha cant help us with.
a block assy from yamaha is just that, a long block with no cyl head.

AGent 37
thats my thought if its not a warrenty item.
as long as the crank journal specs are published we have been building up and regrinding crankshafts for 100 years or more.
the process has gotten much better in the past 30 years.
not much difference between a 16 cyl diesel crank and a weed whacker crank other than cost.
biggest drawback to overhauling an inline 4 stroke in my area is salt corrosion and the time it takes to clean the oil sump coupled with the fact if you follow the steps in the manual you assemble the block about 5 times with the 5th time being the final assy and at 85 an hour it rapidly turns into a rebuild for the cost of new.
but we know its coming, as more and more are out of warrenty we will see more and more failures.
we dont see many of the 4 strokes smaller than the 150. a few 115's but after that most are V6 with twins.

 

[Silvertip]

Re: F100 engine siezed?

Uuuummmm. You said there was "no oil in the crankcase"! That should be a clue as to what happened. The oil pump was not the problem -- lack of oil was. Even the oil pump needs oil to survive. If there was little to no oil in the crankcase none of the moving parts was being lubricated and the big end began to seize. The dipstick is present for a reason and should be checked frequently on a four stroke. In this case, did he not have any audible or visual indication of low oil pressure? Is the alarm system even working and are you sure you got the full and true story?

I have had crankshafts on cars rebuilt that had bearings "welded" to the journal. This actually looks worse than it is. The rebuilders remove the seized parts, weld the journal to build it back up and then finish it to factory specs. Never had one come back and I suspect a four stroke outboard crank would be no different.

 

[rodbolt]

Re: F100 engine siezed?

dunno, but the F yamaha motors dont use undersize bearings.
the bearings for both main and rod are done by actual measurement + or - the stamp mark on the journal or block saddle and the bearings for upper and lower are selected by color coding on a chart then installed and measured with plastiguage. so far they dont really publish the journal or saddle bore size nor the rod big end sizes on a number of F motors.
kinda leaves the machinist grasping.
its a pain enough to use the stamped numbers and the crazy color chart much less try to figgue out what a machinist did or did not do.

as far as welding and regrinding I would only have it done if the shop would warrenty against future failures.
I am not a mettalurgist so I dont know what steel or cast iron was used on the crank but it will make a difference to the welder for rod selection.

no oil in the crankcase or head is rather normal as the oil is in the sump several inches below the crankcase. tilt the engine 5 or 6* positive and it all drains back into the sump.
but I am with silvertip. your descrbing a lubrication failure and possibly an alarm system failure or maybe even a diluted engine oil failure due to fuel in the oil.
whatever the case, carefully inspect everything and dissasemble the oil pan for inspection as well before giving any estimates or quotes.
trust me on this.
while the oil sump is apart carefully check the oil pickup for flatness at the mating surface.
sometimes they warp and leak if they are ever overheated.
I always check them and normally just replace rather than attempt to clean them.