Major engine problems with 8 hp 4 stroke yamaha advice wanted

[dogridgekraus]

Dang I was thinking this thing had a pressed together crank.
Must have thought it was 2 stroke, sorry about that.

Very good question as to what would keep oil from only one rod.
Spun bearing that blocked off oil hole is only thing I can come up with at this time.
Apparently there was oil to everything else or there would be more things damaged

Thanks 99yam40,
Looks just like a typical 4 stroke crank.You had me worried though.lol..
I should have added the pic of the oil sump pan...
A sludged mess to say the least,the oil strainer was all caked up to.
You would think if that was the prob that it would have an equal effect over all & not just one bearing.
The 1st thing I did was look through the oil passage after removeing the crank & could see through it...I don't quite get it???
There was no bearing pieces,Its a "babitted" rod like on the older Chevrolets where the bearings moulded into the rod.I never understood that term is that what it means?It don't have inserts like the main journals do.Maybe it don't have them at all & its just a machined rod.IDK? Youd think it would be more than meets the eye there?
Thanks!
Marty
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[dogridgekraus]

All your pic's showed up. if you double click on each one, they get larger.

I'm surprised that crank isn't more torn up...

Amost missed the crack in the pan...

I think if I would have ran it any longer there would be more than just a crack! lol...
I was a little lery standing next to it when I ran it...
That shouldn't be a big deal to repair though.A friend of mines real good with a tig.
Id like to weld the cracks up from the inside but can see theres a depression made there so clearances must be pretty tight.Im afraid if I welded it up & put it back together if I have too much weld built up in the wrong places then I could screw it up again.
The only positive from welding it up from the inside is it wouldn't be noticeable.
Is what I would prefer...
What would you do,inside or outside?
I guess im thinking too far ahead since im not sure if the crank is good or not.
I mean if I have $400 in it I might as well just go with a good used powerhead I had found.Its looking like I may be able to get buy for less than that though
Thanks!
Marty

[dogridgekraus]

I haven't inspected the oil pump yet either.Worries there...Even if it is wore I think a new one is $115.So if all it takes is a polished journal & a rod to then I guess that would be still under the $400 budget im shooting for.

[rodbolt17]

in the 30 plus powerheads/complete motors I have seen brought to me after an ejunk purchase.
I have not seen one worth buying yet.

typically if a tiny mite motor is for sale there is a reason.

just when you buy something like this with no support its buyer beware.

[TownsendsFJR1300]

That shouldn't be a big deal to repair though.A friend of mines real good with a tig.
Id like to weld the cracks up from the inside but can see theres a depression made there so clearances must be pretty tight.Im afraid if I welded it up & put it back together if I have too much weld built up in the wrong places then I could screw it up again.
The only positive from welding it up from the inside is it wouldn't be noticeable.
Is what I would prefer...
What would you do,inside or outside?

Thanks!
Marty

For proper aluminum TIG repair, he's going to be "V"ing out the crack (should probably try to find the end of the crack and drill to prevent later cracks from developing) and then filling it back in. If done correctly, filing/grinding either side back down to flush will be the same as if new.

There's now, new, un-cracked aluminum there which is usually as strong as the original. So either side is fine but it does appear the inside is machined out for a very close fit. IME, I would hammer it back in slightly(back to original), V grind and weld from the outside. You can clean up the weld or leave it.

Re the failure itself, with all that gunk build up in the pan, the engine obviously wasn't maintained normally and if the oil PU strainer clogged up, that rod /crank just happened to be the weakest link to go first.

Re the lack of a lower rod bearing. In the small 4 stroke (even two stroke) engine world, (referring to mower, generator engines, etc) (even above 10HP), its EXTREMLY rare to have a separate bearing (as in the larger engines with the tab). The rod is the bearing. Should it wear out (very hard to kill unless run hard on NO oil), the rod is simply replaced(if the crank is still good).

With that said, those engine are designed to normally run NO MORE than 3,600 RPM's WOT. They will easily wind up higher than that but aren't designed for a much higher, constant RPM..

I have yet to have a small 4 stroke rod (to crank) fail (in the above engines).

Very, very durable but then they have a "splash" oiling system vs an oil pump on yours that likely clogged up on yours causing lack of oil to that bearing...

Just as a side note, I did have, on a 1976, Yamaha YZ125cc 2 stroke motorcycle(air cooled-dirt bike-pre-mix), with a NEEDLE BEARING (caged) lower crank bearing fail (pressed crank) in an AMA sanctioned MX race way back in the late 70's. Besides needing a new crank pin, side thrust washers, I don't re-call if we replaced the rod or not(probably). Some of the side thrust washers transferred the brass (or copper) to the inside of the crank but was easily removed. No damage to the piston/head as it was shut down immediatly.. Maybe an 8,000 RPM engine back then(guesstamating)..

[dogridgekraus]

Update-T8

Looks like im going to be able to get my outboard repaired & not buy "Ejunk"
Not out of the woods as of yet.
As slugged up as it was im suprized there wasn't majore failure occurring through out,instead that's the only"smokeing gun" I found.I just find that puzzling...
I got the lower end welded up tonight.Had parts cleaning solution in it & didn't see any leakage.

Also had the crank checked for straightness & the crank journal polished,he miked it & said he may have taken .001-.0015 off.Not enough to be down too far to cause a failure he seemed confident saying so.

Question:I ordered the parts from boats.net & wasn't sure on what sized/color bearing to get for the mains.There was 3 colors blue,black & brown.I don't see any trace of color on any of the bearings off my motor.I looked in the manual Almetelo sent me but there wasn't enough info...I didn't know what to do so I just ordered 4 of each of the 3 colors & just send back what I don't need there.
But im not exactly sure how ill figure it out easily.
I don't want to leave any scratches or marks from mikeing or plastic gaugeing to determine this since im going to be sending back what I don't need.IDK...
If you would know please tell???
Maybe a Yamaha dealer could help if I gave them the serial number.IDK.
Thanks again for your time! I appreciate it:
Marty

[rodbolt17]

bearing selection now is going to be hit or miss.
once you select the bearing based on the numbers on the crank and block,use the chart in the manual.
you MUST plastigage it.
plastigage wipes right off.
its simply a plastic strip of a known compressability.

[99yam40]

bearing selection now is going to be hit or miss.
once you select the bearing based on the numbers on the crank and block,use the chart in the manual.
you MUST plastigage it.
plastigage wipes right off.
its simply a plastic strip of a known compressability.

Did you find the numbers Rod is speaking about?

[TownsendsFJR1300]

Just to add, with the plasti gauge, your simply tightening down to spec's and measuring how wide the PG gets. No OIL on the part getting measured. Check your manual, the bolts will probably require oiling when installing.

You WON'T BE spinning over the engine at all (at this point) so nothing should be visable to the bearings(set in block, torqued down, etc)..

Glad to hear your able to save the engine BTW...

[dogridgekraus]

bearing selection now is going to be hit or miss.
once you select the bearing based on the numbers on the crank and block,use the chart in the manual.
you MUST plastigage it.
plastigage wipes right off.
its simply a plastic strip of a known compressability.

I looked at the crank & your right theres a number 4 then a letter P on the balanceing arbor in the center.
In the manual it pointed to where the letters should be & there is none there.
Maybe the F6-F8 manual is not the right manual.I don't see why...It looks like its the same motors there?
I plan on plastic guageing just hate to to that with the bearings I wont need since I don't know if id be able to take them back unpackaged & whatnot...
Happy New Year Rodbolt!
Thanks:
Marty

[dogridgekraus]

Just to add, with the plasti gauge, your simply tightening down to spec's and measuring how wide the PG gets. No OIL on the part getting measured. Check your manual, the bolts will probably require oiling when installing.

You WON'T BE spinning over the engine at all (at this point) so nothing should be visable to the bearings(set in block, torqued down, etc)..

Glad to hear your able to save the engine BTW...

I am happy about being able to salvadge the engine & knowing what I have is always a plus.
I thought about messing around with plastic gauging the old bearings just to see what it was.
They really don't look to bad.Im tempted to just put them back in & not deal with the hassle of figuring out this confuseion.
I figured I would see the color mark on the bearings & order that.I don't see a smidge of any notable colors anywhere on any of them...Sucks...I guess I have to figure this out the hard way or just be a "hack" & forget it...
Im tempted though they really don't look wore...Just fix what is broken,dont fix if it ain't.lol
Thanks Scott,
Happy New Year!
Marty

[dogridgekraus]

Did you find the numbers Rod is speaking about?

I wasn't able to find all of them just number & letter on the crank A,4 & P...
I looked at the manual & I don't see any numbers or letters where there indicateing they should be.
The manual is for an F6-F8 though & mine is the "T" series if theres any diff.IDK...They look the same.
Thanks,
Happy New Year!
Marty

[dogridgekraus]

I was wondering if anyone knows whether this is an "interfierance" engine?
I don't want to accidently bend a valve assembling...
I didn't see anything reguarding precautions about this in the manual but it doesn't mean it isn't...
Thanks;
Marty

[boscoe99]

It is an interference motor.

Here is some general Yamaha information:

"Regardless of whether or not the engine you are working on is an interference engine, get into the habit of removing and installing cylinder heads with
the engine at number one Top Dead Center (TDC) on the compression stroke. This can be easily confirmed by aligning all the timing indicators with their respective marks on the crankshaft and camshaft pulleys."

[dogridgekraus]

So you think I should remove the cylinder head...Just to be cautiouse of the valve timeing?
The pistons can be installed on this motor from the bottom.If im careful it sure would save me the extra work & money yaknow...
I could remove the head,go through the valve seats,valve seals,hone the cylinders,new rings ETC,where does it end, then ill exceed the time & budget I want to put into it.
Everything else looks good.Even the main bearings whitch im starting to think im getting a little carried away there dealing with the hassle of selecting the right bearings...I just ordered all three colors since IDK what color ill need???

Just fixing whats broke & what caused the problem seems like the most economical way to me.I have faith that I can get away with it & it should hold up.
Thanks:
Marty