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Author Topic:   Yamaha blind hole mounting bolts

bikingart posted 11-06-2008 01:30 PM ET (US)
Does anyone know the thread size count for the 1/2" bolts used on the blind holes on a 2004 Yamaha 70 engine mounting bracket ?
Thanks,
Art
contender posted 11-06-2008 08:01 PM ET (US)
Coarse thread 1/2 = 13 per inch, Fine thread 1/2 = 20 per inch
L H G posted 11-06-2008 08:14 PM ET (US)
Don't use blind holes, as they only create rigging problems and wasted holes to re-fill later. One of the worst ideas ever applied to outboards, courtesy of OMC, and then copied by Yamaha.
There is information both here in FAQ and on WhalerCentral on how to install an outboard on an older Whaler with a shallower spashwell. If the vertical center line of the bolts can't be the standard 8", go to either 7-1/4" (which rasies the engine up 3/4", a good thing) or even 6-1/2". You can also move the total set of holes up as much as 7/8" from the original recommendation of 1-7/8" below top of transom. Whaler transoms are strong enough.
See here, where top bolt centerline is 1-1/8 below top, to accomodate an older, shallower transom and still use the standard 8" vertical spacing. The engine is 415# V-6.
http://smg.photobucket.com/albums/v429/lgoltz/Outrage%2021/?action=view& current=DSCN1361.jpg .
contender posted 11-06-2008 08:25 PM ET (US)
LHG why are you against the blind hole? Please explain
L H G posted 11-06-2008 10:23 PM ET (US)
They don't conform with the BIA standard hole pattern that all outboards use, and changing an engine requires un-necessary work of filling and re-gelcoating those odd bolt holes. Also strikes me as not as secure as through-bolting.
I just spent a few days repairing extra transom bolt holes un-rigging twin Johnson 70's where the installer had used these, when he didn't need to. A lot of extra work. Mercury, Honda and Suzuki have never used this gimmick. Don't know whether BRP and Yamaha are using them in recent designs.
contender posted 11-07-2008 03:28 PM ET (US)
LHG my question to you was because I used the blind mounting holes on my Evinrude 140 looper (1985) on a 1975 16'7" whaler. I was unable to use the lower mounting bolt holes due to the make up of the splash well on the whaler being to shallow. I could not mount the engine any higher due to the position of the cavitation plate on the engine and the bottom of the boat. Also the top mounting holes would have been to close to the top of the transom. When I rigged my boat jack plates were just coming out and I did not know enough about them to use one. As far as the strength I believe it is the same as a bolt going through the mount hole,(same size bolt same amount of threads). I do agree with you about not being a standard bolt pattern,(and do not know why the person choose to use them I would have not if I did not have to) but then how often do you change your engine? I have been thinking about replacing my engine with a new Evinrude 130. However, I would also be purchasing a new jack plate to go with it. I would try to mount the jack plate using the old mounting holes I have in the transom now...I understand what you are saying but I needed/used them.
foghorn posted 11-07-2008 04:41 PM ET (US)
I believe the Yamaha blind holes are 12 mm, fine thread,
1.25 pitch. They were on my 2003.
Tom W Clark posted 11-07-2008 04:52 PM ET (US)
I agree with Larry. There is no good reason to use the blind holes in this day and age.
A 1985 Evinrude 140 can easily be mounted on a 1975 16'-7" Whaler hull using the very top of the lower bolt slot along with the third set of top bolt holes. This will raise the motor 1-1/2" above the transom and allow the lower bolts to clear the splashwell.
The cavitation plate will be about 1-1/4" above the bottom of the keel which will be fine if an appropriate propeller is used.
The next lower set of bolts can also be used if the lower bolts are angled upwards a bit *or* if the washers in the splashwell for the lower bolts have the lower edge cut off to help them nest at the very bottom of the splashwell.
contender posted 11-07-2008 11:18 PM ET (US)
Tom, I rigged the whaler back in 1985, I'm pretty sure this was the route I had to take, If I raise the engine as you stated there was not enough meat left on the transom for the top bolts, also the cav. plate would have been to high. My engine (cavitation plate) is sitting about 1 1/2 inches above the bottom of the boat now with the engine on the transom.
Tom W Clark posted 11-07-2008 11:34 PM ET (US)
No way. Any OMC long shaft motor, any model year, mounted on a 16'-7" classic Whaler hull will have its cavitation plate well below the hull if mounted all the way down.
The upper bolt holes stay the same no matter how high you mount the motor. There is no need to drill them higher.
contender posted 11-09-2008 07:17 PM ET (US)
Did not say it was below the hull stated it is were it needs to be, mounted on the transom, If I move it up it would be to high...
Tom W Clark posted 11-09-2008 08:20 PM ET (US)
Rick,
You are confusing us. What you said was:
"My engine (cavitation plate) is sitting about 1 1/2 inches above the bottom of the boat now with the engine on the transom"
I say this is not possible unless the transom is modified or you do not have a 20" shaft length OMC motor.
Can you clarify where your motor is?
contender posted 11-09-2008 09:21 PM ET (US)
Tom: not trying to argue (and I think from reading you threads you know more than me) with you so bear with me here. This is what I have. 1975 16'7' whaler with a 1985 140hp Evinrude looper, short shaft. The engine is mounted (resting on the transom) and the cavitation plate is 1" above the bottom of the boat. Also being a 140 hp I felt the boat would have no problem getting out of the water/on a plane and I wanted the engine to get/pick up water. The transom has not been modified. I used the two blind holes for the bottom two bolts. If I would have raised the engine the cavitation plate would have been to high and I did not feel that enough meat would have been left on the transom for the top bolts holes. I could not use the other (bottom) mounting holes due to the shallow design of the whalers splash well. I'm now in the process of redoing the whaler (its 33 years old needs some glass work, paint, new console, steering and I'm looking at a jack plate) I will probably will reuse the same holes for the jack plate (or make the jack plate fit them). Another nice thing I have notice when the whaler is sitting in the water the blind holes are high out of the water. So other than using a jack plate which at the time of the rigging (1985), I did not know enough about them to use one, I think I have set it up correctly. Oh yeah and its in the center of the transom... Thanks
Tom W Clark posted 11-09-2008 09:45 PM ET (US)
Rick,
The point I was trying to make is that if your cavitation plate is 1" or 1-1/2" (you have stated it both ways) above the keel, then your motor is not mounted as low as it could be. It is mounted one or maybe two holes up.
The heart of the matter is this: If you motor is mounted one hole up (3/4" above the top of the transom) or two holes up (1-1/2" above the top of the transom) then you do not need to use the blind holes. You can use the very upper end of the lower bolt slot and the bolts will clear the splashwell just fine.
If I may disambiguate what you have written a bit further, you have along shaft motor (20") not a short shaft motor (15"). Is that not correct? If you actually have a 15" shaft length motor then none of this applies.
And also for the sake of others reading this, let me point out that the upper holes in the transom do not need to change regardless of how high the motor is mounted.
The centers of the upper holes are drilled through the transom 1-3/4" to 1-7/8" below the top edge of the transom and the motor than can be then mounted right down to top of the transom or 3/4", 1-1/2" or 2-1/4" above the top of the transom. In the case of Mercury outboards which have five bolt holes not just four, you can raise the motor as much as a full 3" above the top of the transom.
There is not any concern about "the top mounting holes [being] to close to the top of the transom." They stay where they are regardless of how the motor is mounted.
contender posted 11-09-2008 11:25 PM ET (US)
Tom; I will find someone to teach me how to send you some pictures. You are correct about the shaft length 20 inches (I though 20 inch was the short shaft) I measured the cavitation plate and its 1 inch above the bottom of the boat. And the engine is resting on the transom. Question: In 1985 the 140 looper was this not the only year it came with a different lower unit? (I'm not sure if this is true or that it matters?) Thanks
Tom W Clark posted 11-10-2008 10:41 AM ET (US)
Short Shaft = 15"
Long Shaft = 20"
Extra Long Shaft = 25"
Extra, Extra Long Shaft = 30"
A photo is worth a thousand words. Yes, please send a photo.
When you say "...the engine is resting on the transom." Does that mean it is bolted to the transom and not a jack plate, or are you saying the "hooks" are down on the top of the transom?
If the latter, then there is no way the cavitation plate is above the bottom of the hull.
contender posted 11-10-2008 09:16 PM ET (US)
Tom: No jack plate, Hooks are on the transom, and it is bolted in place. I will try to get you the pictures one way or another, thanks
Tom W Clark posted 11-12-2008 11:58 AM ET (US)
Rick,
You can email a photo to either if my two email addresses. I'm not trying to give you a hard time I just want to make sure that the other hundreds of guys reading this, and those who will read this in the future while researching the topic, come away with a clear picture.
While this topic is an FAQ from the reference section, it still comes up over and over again. The blind hole accommodation developed by OMC back in the 1960s and copied by Yamaha a decade later made good sense 30 or 40 years ago, but it does not apply (at least not to Whalers) with today's propellers.
Let me repeat what Larry was trying to say above:
There is no good reason to use the blind holes when mounting an outboard motor to a Whaler.
contender posted 11-12-2008 01:35 PM ET (US)
Tom, I will not skirt the issue nor make it an issue because I'm just as surprise as you may be. I really though the blind holes were great and accommodated me when mounting the engine. I'm just not computer smart I do not know how to transfer the pictures to the computer/email, and trying to get someone to help is not easy. If I have to I will just mail you the pictures. I'm leaving Friday night for 4 days and will be back on Tuesday, I hope to have some pictures for you by then either way. I looked at it again last night, I leveled the engine(using the trim and a 2' level) and the cavitation plate came to the bottom of the drain hole/plug which is about 1 inch above the bottom of the boat, the engine sits right on the factory transom (you can see the green line). Tom: Question: Why were the blind holes put on the engines in the first place? Was it for a special application? Designed for a certain boat?...thanks
Tom W Clark posted 11-12-2008 07:34 PM ET (US)
Rick,
Shoot me an email and I can coach you on how to attach a photo to an email. If you do it once, it will be easy for you do again.
The reason for OMC developing the blind holes (or auxiliary holes as they were in the 1960s) was to allow a motor to be mounted to a hull where access to the lower bolt holes was difficult.
The 16'-7" whaler was a good example of this where you had to mount the motor as low as possible to make sure the propeller was well submerged. Remember the motor mounting advice from back then was to be sure the cavitation plate was at least an inch below the hull so it would remain fully submerged.
Back then virtually all propellers were aluminum with no cupping and they would ventilate of they got too close to the surface of the water. It became standard operating procedure to mount an outboard on the 16/17 Whalers all the way down using the blind holes.
Many long time dealers/mechanic still do this today from old habits. But with modern cupped stainless steel propellers, the motors should really be mounted with the cavitation plate an inch above the keel so it clears the surface while the boat is on plane and does not contribute drag and cause spray.
Manufacturers, like Mercury, who never offered an alternative the lower bolt holes, often saw their motors mounted to Whalers (tragically) with the hull cut open and foam carved out to reach the lower bolt holes.
I have seen all manner of pry-outs installed in the splashwell, the face of the splashwell and bad patch jobs as ignorant installers think they have to put the motor all the way down. It still happens today and it just breaks my heart when a hull that is 30 or 40 years old and was never cut open gets a hack job with a new motor today.


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Author	Topic: Yamaha blind hole mounting bolts
bikingart	posted 11-06-2008 01:30 PM ET (US) Does anyone know the thread size count for the 1/2" bolts used on the blind holes on a 2004 Yamaha 70 engine mounting bracket ? Thanks, Art
contender	posted 11-06-2008 08:01 PM ET (US) Coarse thread 1/2 = 13 per inch, Fine thread 1/2 = 20 per inch
L H G	posted 11-06-2008 08:14 PM ET (US) Don't use blind holes, as they only create rigging problems and wasted holes to re-fill later. One of the worst ideas ever applied to outboards, courtesy of OMC, and then copied by Yamaha. There is information both here in FAQ and on WhalerCentral on how to install an outboard on an older Whaler with a shallower spashwell. If the vertical center line of the bolts can't be the standard 8", go to either 7-1/4" (which rasies the engine up 3/4", a good thing) or even 6-1/2". You can also move the total set of holes up as much as 7/8" from the original recommendation of 1-7/8" below top of transom. Whaler transoms are strong enough. See here, where top bolt centerline is 1-1/8 below top, to accomodate an older, shallower transom and still use the standard 8" vertical spacing. The engine is 415# V-6. http://smg.photobucket.com/albums/v429/lgoltz/Outrage%2021/?action=view& current=DSCN1361.jpg .
contender	posted 11-06-2008 08:25 PM ET (US) LHG why are you against the blind hole? Please explain
L H G	posted 11-06-2008 10:23 PM ET (US) They don't conform with the BIA standard hole pattern that all outboards use, and changing an engine requires un-necessary work of filling and re-gelcoating those odd bolt holes. Also strikes me as not as secure as through-bolting. I just spent a few days repairing extra transom bolt holes un-rigging twin Johnson 70's where the installer had used these, when he didn't need to. A lot of extra work. Mercury, Honda and Suzuki have never used this gimmick. Don't know whether BRP and Yamaha are using them in recent designs.
contender	posted 11-07-2008 03:28 PM ET (US) LHG my question to you was because I used the blind mounting holes on my Evinrude 140 looper (1985) on a 1975 16'7" whaler. I was unable to use the lower mounting bolt holes due to the make up of the splash well on the whaler being to shallow. I could not mount the engine any higher due to the position of the cavitation plate on the engine and the bottom of the boat. Also the top mounting holes would have been to close to the top of the transom. When I rigged my boat jack plates were just coming out and I did not know enough about them to use one. As far as the strength I believe it is the same as a bolt going through the mount hole,(same size bolt same amount of threads). I do agree with you about not being a standard bolt pattern,(and do not know why the person choose to use them I would have not if I did not have to) but then how often do you change your engine? I have been thinking about replacing my engine with a new Evinrude 130. However, I would also be purchasing a new jack plate to go with it. I would try to mount the jack plate using the old mounting holes I have in the transom now...I understand what you are saying but I needed/used them.
foghorn	posted 11-07-2008 04:41 PM ET (US) I believe the Yamaha blind holes are 12 mm, fine thread, 1.25 pitch. They were on my 2003.
Tom W Clark	posted 11-07-2008 04:52 PM ET (US) I agree with Larry. There is no good reason to use the blind holes in this day and age. A 1985 Evinrude 140 can easily be mounted on a 1975 16'-7" Whaler hull using the very top of the lower bolt slot along with the third set of top bolt holes. This will raise the motor 1-1/2" above the transom and allow the lower bolts to clear the splashwell. The cavitation plate will be about 1-1/4" above the bottom of the keel which will be fine if an appropriate propeller is used. The next lower set of bolts can also be used if the lower bolts are angled upwards a bit or if the washers in the splashwell for the lower bolts have the lower edge cut off to help them nest at the very bottom of the splashwell.
contender	posted 11-07-2008 11:18 PM ET (US) Tom, I rigged the whaler back in 1985, I'm pretty sure this was the route I had to take, If I raise the engine as you stated there was not enough meat left on the transom for the top bolts, also the cav. plate would have been to high. My engine (cavitation plate) is sitting about 1 1/2 inches above the bottom of the boat now with the engine on the transom.
Tom W Clark	posted 11-07-2008 11:34 PM ET (US) No way. Any OMC long shaft motor, any model year, mounted on a 16'-7" classic Whaler hull will have its cavitation plate well below the hull if mounted all the way down. The upper bolt holes stay the same no matter how high you mount the motor. There is no need to drill them higher.
contender	posted 11-09-2008 07:17 PM ET (US) Did not say it was below the hull stated it is were it needs to be, mounted on the transom, If I move it up it would be to high...
Tom W Clark	posted 11-09-2008 08:20 PM ET (US) Rick, You are confusing us. What you said was: "My engine (cavitation plate) is sitting about 1 1/2 inches above the bottom of the boat now with the engine on the transom" I say this is not possible unless the transom is modified or you do not have a 20" shaft length OMC motor. Can you clarify where your motor is?
contender	posted 11-09-2008 09:21 PM ET (US) Tom: not trying to argue (and I think from reading you threads you know more than me) with you so bear with me here. This is what I have. 1975 16'7' whaler with a 1985 140hp Evinrude looper, short shaft. The engine is mounted (resting on the transom) and the cavitation plate is 1" above the bottom of the boat. Also being a 140 hp I felt the boat would have no problem getting out of the water/on a plane and I wanted the engine to get/pick up water. The transom has not been modified. I used the two blind holes for the bottom two bolts. If I would have raised the engine the cavitation plate would have been to high and I did not feel that enough meat would have been left on the transom for the top bolts holes. I could not use the other (bottom) mounting holes due to the shallow design of the whalers splash well. I'm now in the process of redoing the whaler (its 33 years old needs some glass work, paint, new console, steering and I'm looking at a jack plate) I will probably will reuse the same holes for the jack plate (or make the jack plate fit them). Another nice thing I have notice when the whaler is sitting in the water the blind holes are high out of the water. So other than using a jack plate which at the time of the rigging (1985), I did not know enough about them to use one, I think I have set it up correctly. Oh yeah and its in the center of the transom... Thanks
Tom W Clark	posted 11-09-2008 09:45 PM ET (US) Rick, The point I was trying to make is that if your cavitation plate is 1" or 1-1/2" (you have stated it both ways) above the keel, then your motor is not mounted as low as it could be. It is mounted one or maybe two holes up. The heart of the matter is this: If you motor is mounted one hole up (3/4" above the top of the transom) or two holes up (1-1/2" above the top of the transom) then you do not need to use the blind holes. You can use the very upper end of the lower bolt slot and the bolts will clear the splashwell just fine. If I may disambiguate what you have written a bit further, you have along shaft motor (20") not a short shaft motor (15"). Is that not correct? If you actually have a 15" shaft length motor then none of this applies. And also for the sake of others reading this, let me point out that the upper holes in the transom do not need to change regardless of how high the motor is mounted. The centers of the upper holes are drilled through the transom 1-3/4" to 1-7/8" below the top edge of the transom and the motor than can be then mounted right down to top of the transom or 3/4", 1-1/2" or 2-1/4" above the top of the transom. In the case of Mercury outboards which have five bolt holes not just four, you can raise the motor as much as a full 3" above the top of the transom. There is not any concern about "the top mounting holes [being] to close to the top of the transom." They stay where they are regardless of how the motor is mounted.
contender	posted 11-09-2008 11:25 PM ET (US) Tom; I will find someone to teach me how to send you some pictures. You are correct about the shaft length 20 inches (I though 20 inch was the short shaft) I measured the cavitation plate and its 1 inch above the bottom of the boat. And the engine is resting on the transom. Question: In 1985 the 140 looper was this not the only year it came with a different lower unit? (I'm not sure if this is true or that it matters?) Thanks
Tom W Clark	posted 11-10-2008 10:41 AM ET (US) Short Shaft = 15" Long Shaft = 20" Extra Long Shaft = 25" Extra, Extra Long Shaft = 30" A photo is worth a thousand words. Yes, please send a photo. When you say "...the engine is resting on the transom." Does that mean it is bolted to the transom and not a jack plate, or are you saying the "hooks" are down on the top of the transom? If the latter, then there is no way the cavitation plate is above the bottom of the hull.
contender	posted 11-10-2008 09:16 PM ET (US) Tom: No jack plate, Hooks are on the transom, and it is bolted in place. I will try to get you the pictures one way or another, thanks
Tom W Clark	posted 11-12-2008 11:58 AM ET (US) Rick, You can email a photo to either if my two email addresses. I'm not trying to give you a hard time I just want to make sure that the other hundreds of guys reading this, and those who will read this in the future while researching the topic, come away with a clear picture. While this topic is an FAQ from the reference section, it still comes up over and over again. The blind hole accommodation developed by OMC back in the 1960s and copied by Yamaha a decade later made good sense 30 or 40 years ago, but it does not apply (at least not to Whalers) with today's propellers. Let me repeat what Larry was trying to say above: There is no good reason to use the blind holes when mounting an outboard motor to a Whaler.
contender	posted 11-12-2008 01:35 PM ET (US) Tom, I will not skirt the issue nor make it an issue because I'm just as surprise as you may be. I really though the blind holes were great and accommodated me when mounting the engine. I'm just not computer smart I do not know how to transfer the pictures to the computer/email, and trying to get someone to help is not easy. If I have to I will just mail you the pictures. I'm leaving Friday night for 4 days and will be back on Tuesday, I hope to have some pictures for you by then either way. I looked at it again last night, I leveled the engine(using the trim and a 2' level) and the cavitation plate came to the bottom of the drain hole/plug which is about 1 inch above the bottom of the boat, the engine sits right on the factory transom (you can see the green line). Tom: Question: Why were the blind holes put on the engines in the first place? Was it for a special application? Designed for a certain boat?...thanks
Tom W Clark	posted 11-12-2008 07:34 PM ET (US) Rick, Shoot me an email and I can coach you on how to attach a photo to an email. If you do it once, it will be easy for you do again. The reason for OMC developing the blind holes (or auxiliary holes as they were in the 1960s) was to allow a motor to be mounted to a hull where access to the lower bolt holes was difficult. The 16'-7" whaler was a good example of this where you had to mount the motor as low as possible to make sure the propeller was well submerged. Remember the motor mounting advice from back then was to be sure the cavitation plate was at least an inch below the hull so it would remain fully submerged. Back then virtually all propellers were aluminum with no cupping and they would ventilate of they got too close to the surface of the water. It became standard operating procedure to mount an outboard on the 16/17 Whalers all the way down using the blind holes. Many long time dealers/mechanic still do this today from old habits. But with modern cupped stainless steel propellers, the motors should really be mounted with the cavitation plate an inch above the keel so it clears the surface while the boat is on plane and does not contribute drag and cause spray. Manufacturers, like Mercury, who never offered an alternative the lower bolt holes, often saw their motors mounted to Whalers (tragically) with the hull cut open and foam carved out to reach the lower bolt holes. I have seen all manner of pry-outs installed in the splashwell, the face of the splashwell and bad patch jobs as ignorant installers think they have to put the motor all the way down. It still happens today and it just breaks my heart when a hull that is 30 or 40 years old and was never cut open gets a hack job with a new motor today.