1988 OMC Cobra 7.5L Engine DEAD?

[Joshua Nichols]

Re: 1988 OMC Cobra 7.5L Engine DEAD?

This is NOT a "Cone" drive (no cone clutch drives in 1988) There was no cone-clutch drive behind the 460 until 1990 and they dropped the 460 after that.

His drive is a Dog-clutch model.

I am aware of what he has.. I looked at the break down(never saw a dog clutch in the parts list).. Looks different than the regular cobra

I was just thinking the cone was a tougher design.. I guess it makes no difference since he doesn't have one

 

[HT32BSX115]

Re: 1988 OMC Cobra 7.5L Engine DEAD?

I am aware of what he has.. I looked at the break down(never saw a dog clutch in the parts list).. Looks different than the regular cobra

I was just thinking the cone was a tougher design.. I guess it makes no difference since he doesn't have one

I wouldn't say that the cone is necessarily a "tougher" design as much it's a far BETTER design. (it could be tougher but because of the way they connect and separate, they don't have to be)

Which parts list are you referring to?

In the BRP parts list for the 1987 (460King Cobra) lower case I found the following.........

#910995 (Shifter, Clutch dog)

1988 & 1989 7.5L King Cobra Lower

#334516 (Shifter, Clutch dog)



Sierra by the way indicates that #18-2216 (Sliding Clutch) replaces OMC 337772 OMC 336562 OMC 334516 OMC 337774 OMC 910995
(emphasis mine)

So it would indicate that the clutch dog for 1987,1988,1989 7.5L drives are identical. And it also looks like they used that same "dog-clutch" (sliding-clutch etc) in several different (probably BIG) outboard lower cases too.

However, OMC #912626 (5.7L Cobra lower "Shifter, Clutch Dog") doesn't appear to be usable in a 7.5L lower......

You can look all these part numbers up at http://epc.brp.com, http://www.marinepartsplus.com and many other places that deal in obsolete OMC parts.



I'll also add that the OP claims he is using one the smaller drives. Because the pivot housing is the same, across all the Cobras,
Even the smallest Cobra (that holds around 60oz of oil) could be "bolted" to the 460 King Cobra (that holds 108oz of oil) transom mount.

Of course the gear ratios would all wrong, but with the right length yoke I suppose it would work......Donno how long it would last though.

The vertical drive shaft assy is supposed to be a weak point (and not available) in the King Cobra drive..... It has to be even weaker in
the smaller drives.... but available probably from Sierra etc





Cheers,


Rick

 

[Joshua Nichols]

Re: 1988 OMC Cobra 7.5L Engine DEAD?

Sorry Rick...I was looking at the wrong model number...:facepalm: Was trying to figure out what the heck this was 0913474
BUSHING, Thrust. on the 744AMRGDP but he is a 75...

I love Four Winns.. Great boat.(Pictures?). Still I would get out of that problem child and find something different. Working on em isn't near as fun as riding in em.... Funny thing... The OMC stuff in it is likely worth more than the boat.. I see it selling on Ebay like Gold....

 

[SSLAGH]

Re: 1988 OMC Cobra 7.5L Engine DEAD?

Ok, boat is running and cooling properly on muffs. However during the lake test the mech says it started to overheat , about half way up the gage , so he shut it off to find out why it's not cooling via a lake test. Considering all the info above , any suggestions as to what to look for? Is there anything that an overheat condition can affect / plug / screw up in the water pump impeller function that would make the engine get hot , especailly at higher RPM's?

 

[HT32BSX115]

Re: 1988 OMC Cobra 7.5L Engine DEAD?

Marine engines are easy to cool if there's enough water FLOW. That comes from the raw water pump. If the flow from the pump is full of bubbles or insufficient, you get overheats.

If the water cannot get out (through the manifolds/risers) then the overall flow is reduced causing overheats.

Clogged passages in the block, heads, t-stat housing, risers, can also cause it.

Before you go looking for all those problems, determine if you actually HAVE an overheat. Get another known gage, sender or a cheap infrared temp gage like the $29.95 Harbor freight one and ensure that your gage isn't lying to you

Ok, boat is running and cooling properly on muffs. However during the lake test the mech says it started to overheat , about half way up the gage ,

Also, when a pump will not prime under it's own "power" but everything is ok with a pressure water source(hose), It's frequently a problem with how the pump is plumbed or installed (sucking air etc.....)

Funny thing... The OMC stuff in it is likely worth more than the boat.. I see it selling on Ebay like Gold....

Yeah..... I have told more than one person here that over a 2-3 period, I sold ALL my previously installed OMG 460 King Kobra junk for a grand total of $3500!! and I kept the alt bracket, alt, fuel filter mount, remote oil filter mounting stuff and a few other things!

 

[SSLAGH]

Re: 1988 OMC Cobra 7.5L Engine DEAD?

Also, when a pump will not prime under it's own "power" but everything is ok with a pressure water source(hose), It's frequently a problem with how the pump is plumbed or installed (sucking air etc.....)

Thanks for your patience and all your input first of all . Would it be likely if any of the aforementioned issues ( clogged block, risers ,etc) were present , that the engine would run at normal operating temp with the hose , but not in the lake? I would think if it was any of those issues the overheat would occur even with the hose pressure/ muffs. Just trying to narrow it down , paying the mechanic to troubleshoout this thing is getting way expensive, I know ........you told me.......

 

[HT32BSX115]

Re: 1988 OMC Cobra 7.5L Engine DEAD?

Any engine wil run fine with a hose pushing water in. Since it's not making much power (and heat) it doesn't get very hot.

They only get how when the rejected heat is less than the generated heat.

At idle, you don't make much heat......but when you load the engine you create a LOT of heat that must be carried away with water.....if you don't carry away enough heat, the engine heats up. (One of those stupid laws of thermodynamics....I can't remember which one!!)

If it's overheating in the lake at idle. The pump is either not working or it's sucking air someplace.....

 

[SSLAGH]

Re: 1988 OMC Cobra 7.5L Engine DEAD?

Ok, next saga . Mechanic is saying the water impeller comes off water impeller shaft under high rpm, fine at lower rpm. Suggestion is that this shaft has moved or is otherwise out of alighment. Looking at the part diagram on BRP, there seems to be a shim # 33 in differant thicknesses. Is this part ( or any other ) meant to compensate for wear on the location of the water impeller shaft over time, and the ability to keep the impeller working ? Are there specialty tools needed to fix this issue? Any other suggestions as to why the impeller would be failing only at higher RPM? 1988 460 7.5l 754BPRGDP

[URL="http://epc.brp.com/Index.aspx?lang=E&s1=cbc0a4ad-fb29-4987-ba7b-9cc8c74cbc9a

View attachment 112912

 

[HT32BSX115]

Re: 1988 OMC Cobra 7.5L Engine DEAD?

Ok, next saga . Mechanic is saying the water impeller comes off water impeller shaft under high rpm, fine at lower rpm. Suggestion is that this shaft has moved or is otherwise out of alighment. Looking at the part diagram on BRP, there seems to be a shim # 33 in differant thicknesses. Is this part ( or any other ) meant to compensate for wear on the location of the water impeller shaft over time, and the ability to keep the impeller working ? Are there specialty tools needed to fix this issue? Any other suggestions as to why the impeller would be failing only at higher RPM? 1988 460 7.5l 754BPRGDP

[URL="http://epc.brp.com/Index.aspx?lang=E&s1=cbc0a4ad-fb29-4987-ba7b-9cc8c74cbc9a

View attachment 112912

I don't think so. That shim is more for gear alignment/preload etc than for anything related to the the water pump impeller.

I would replace the impeller. It sounds like the impeller might be defective.

If I remember correctly, there's no KEY or slot. The impeller aligns with a flat/"half-round" on the shaft.

If it doesn't fit tightly, the impeller is either the wrong one, defective, or the shaft is damaged etc.....

 

[SSLAGH]

Re: 1988 OMC Cobra 7.5L Engine DEAD?

Thanks so much for following my posts, now we're getting to the details I think

I'm on my 2nd new impeller since the overheat, impeller (both) fit tight and I have been assured that it is the correct impeller. ( you're correct on the half round connection) .
Plus , the water flow is good at low RPM, per mechanic, once the RPM is increased to 3500 aprox, that's when the impeller fails to pump water to the engine????

Do you have any experience with a damaged/ misaligned shaft ? Are there special tools to replace / repair the shaft? Can you think of anything that drives the impeller or impeller shaft that would mess up or misalign, only under a higher RPM ?

I wonder if this wasn't my problem all along, since I replaced the impeller at the end of the last season ( Oct 2010) , and maybe this condition occured once the RPM was up above the 3000 mark when my origanal overheat occured (8/13/2011)

 

[HT32BSX115]

Re: 1988 OMC Cobra 7.5L Engine DEAD?

Well it's hard to know without seeing the thing. There's really no way to mis-align the shaft.

The only other things I can think of is that you're using the wrong impeller or something is installed wrong.......

BUT All the raw water pumps from the little Cobra all the way up to the "big" one use the same one.



Those cobra water pumps are pretty rugged if you keep them wet. Mine routinely ran up to 5000RPM and never had a problem.