Bravo Lower Tolerances??

[Geronimo36]

Can someone tell me what measurements they're setting up big HP Bravo XR lower unit tolerances. (pinion depth and backlash)

I already have what the merc manual calls for but looking to see what everyone on the outside is setting tolerances for big HP engines. I'm going thru a set right now and if there is any variance from stock tolerance I'd like to give it a shot and see if it makes a difference.

Thanks in Advance!

[smittyseng]

Can someone tell me what measurements they're setting up big HP Bravo XR lower unit tolerances. (pinion depth and backlash)

I already have what the merc manual calls for but looking to see what everyone on the outside is setting tolerances for big HP engines. I'm going thru a set right now and if there is any variance from stock tolerance I'd like to give it a shot and see if it makes a difference.

Thanks in Advance!

I set my lower gears up at 13-15 thousandths b/l,they seem to last longer a little loose (in my experience). As far as the depth I set it to the factory spec with the tool and a feeler gauge,Smitty

[MarylandMark]

No more Bmax?

[Mr Gadgets]

As Smitty says, back lash .012"-.015" and depth is at .025". If you find and variation in lash check to see that the pinion gear sits on the shaft without runout. I turn the end of the race down to correct it.
Dick

[Geronimo36]

As Smitty says, back lash .012"-.015" and depth is at .025". If you find and variation in lash check to see that the pinion gear sits on the shaft without runout. I turn the end of the race down to correct it.
Dick


I set my lower gears up at 13-15 thousandths b/l,they seem to last longer a little loose (in my experience). As far as the depth I set it to the factory spec with the tool and a feeler gauge,Smitty

Thanks guys! Before putting in new bearings and races I came up with .035 on pinion depth:eek::boxing_smiley: Gonna put in new bearings and races and see what it comes out at and then shim from there. They seem to think it could be the bearing tolerances (I doubt .010 is in the bearing).. I think the lowers may have been built on a Monday...:ack2:


No more Bmax?

BMax HT lowers are essentially the same as an XR Sportmaster. They have a thicker vertical shaft, an upgraded propshaft, a caged vertical shaft bearing and coated gears. When the HT upper grenaded it sent some metal down into the lower so I tore that one down and also the other one to go thru them both and at minimum replace all bearings/seals..

When you run power this big you have to check this stuff out on a regular basis, it makes for fun winter projects. :)

[Geronimo36]

I really didn't think there would be ten thou in the vertical shaft bearings, maybe the new race above the pinion was a little bigger than the old one but I put in the new bearings/races and now the tolerances are dead balls accurate. :)

[LS1Nova]

Just curious, did you check it in 3 spots to see if there is any runout? Seems pretty odd that your shaft would move up .010" without having significant wear on the lower bearing. If it were me I would smack the lower race with the bearing driver a couple more times and recheck it just to make sure. But then again I loose sleep if a wrench is out of place in my tool box:ack2:

If you still have your old bearing it would be nice to get a measurement from them vs the new ones also. Maybe that would give you a solid explanation.

[Geronimo36]

Just curious, did you check it in 3 spots to see if there is any runout? Seems pretty odd that your shaft would move up .010" without having significant wear on the lower bearing. If it were me I would smack the lower race with the bearing driver a couple more times and recheck it just to make sure. But then again I loose sleep if a wrench is out of place in my tool box:ack2:

If you still have your old bearing it would be nice to get a measurement from them vs the new ones also. Maybe that would give you a solid explanation.

I checked everything 3 times and even removed the races to make sure I didn't add/remove a shim etc. Thanks anyway for the suggestion but it was basically what I did when I assembled it. :)

[Mr Gadgets]

Geronimo,
I have found that using different brand bearings can make big diff in the height of the gear. Another thing is if the bearing race caught any metal on the way in, it could add .010" to the height. It is hard to measure the race and see and difference to compare. But if it seated when you drove home (you can hear it when it does seat) and the measurement comes out.. I wouldnt loose any sleep.
How much runout did you have around the gear?

Dick

[Clustergear]

Got some free time today and rebuild both of my lower units. Used Merc gear kits They have all seal, shims, gears and bearings. When you order as kit you save alot of money, So its like you get so of the parts free. I set them up to Merc specs. Remember when you do prop shaft pre-load, the total is pinion pre-load plus 8-12 in lbs. I like to use shims for prop shaft pre load on my own drives insted of crush collar becasue if you want to go inside lower in a hurry to check something or pull carrier while drive is on boat, you pull it out and tighten it back back up.

[Geronimo36]

Another thing is if the bearing race caught any metal on the way in, it could add .010" to the height.

How much runout did you have around the gear?

Actually, I removed the race and double checked everything and re-pressed the race back into place because it had my scracting me head. What you say about the different bearings could be correct because I put a set of CMC bearings in.

Height was the same all around.

Looks like I'm not going to loose any sleep over the difference but the only thing I may loose a little sleep over is the pinion was installed .010 shallow with about 20 hours for the season. I didn't build them last winter so I don't know if they were set up properly. I'm not a big fan of secondary wear patterns on gears but I'm going to see how it goes.... Probably pull them down after a few runs next year and see if the new depth made any difference.

[Geronimo36]

Got some free time today and rebuild both of my lower units. Used Merc gear kits They have all seal, shims, gears and bearings. When you order as kit you save alot of money, So its like you get so of the parts free. I set them up to Merc specs. Remember when you do prop shaft pre-load, the total is pinion pre-load plus 8-12 in lbs. I like to use shims for prop shaft pre load on my own drives insted of crush collar becasue if you want to go inside lower in a hurry to check something or pull carrier while drive is on boat, you pull it out and tighten it back back up.

That's cool! My own drives are almost finished but in the meantime I'm doing another for a friend.

[Bill N]

That's cool! My own drives are almost finished but in the meantime I'm doing another for a friend.

Thanks!

[Geronimo36]

Thanks!

Anytime, my pleasure!

Feel free to drop off the cases anytime!