Author Topic: CB750K Engine - Broken Gusset (Read 3168 times)

BRAD CHIEDUCH · « **on:** September 12, 2016, 06:10:34 PM »

I am going to resurrect a previous post (http://forums.sohc4.net/index.php?topic=115414.0) as I have experienced the exact same problem as did Maksimum Hops in his posting. I have attached the picture from his posting but mine is pretty much identical. There is a web/gusset on the main bearing tower next to the primary chain tensioner. The top corner of this web/gusset snapped off and was found laying in the bottom of the case. This gusset is directly underneath the cam chain. Firstly, I am uncertain of the purpose for this gusset - I don't believe the intent was for supporting the main bearing as none of the other main bearings have this support. My guess is it eliminates oil windage between the primary chain and cam chain. Perhaps someone with a larger hat size than mine can comment how critical this piece of metal is and whether it should be repaired or can I live without it. I could blend and smooth out the edge of the remaining gusset or attempt a weld repair. TIG welding cast aluminum has its challenges with miscellaneous garbage alloys spitting and popping while welding but I am tempted to give it a try.

Most of us I'm sure would rather not have loose pieces of shrapnel in our engines and I really would like to know what caused this problem as to avoid it in the future. Interesting thing is I am not the only one that has encountered this problem. I didn't see how close the cam chain comes to the top of the gusset - maybe a loose chain whipping around could have been the culprit at some point in time. Like I say comments from guys wearing ten gallon hats versus my beanie are greatly appreciated.

Don R · « **Reply #1 on:** September 12, 2016, 07:50:07 PM »

Where's Hondaman! I'd say it probably ran without it for a while it would run without it some more. I'd agree it's likely for windage or something, too thin to be of much structural use.

disco · « **Reply #2 on:** September 13, 2016, 12:45:09 AM »

Hi Spedwobl,

I don't know the purpose, but I'm interested to find out more too. I checked my F0 case (CB750E-254XXXX) as it's open at moment, and that web appears to finish a little further down I think?

rotortiller · « **Reply #3 on:** September 13, 2016, 04:21:51 AM »

Might be to distribute oil like a dam or deflector, definitely adds little reinforcing.

BRAD CHIEDUCH · « **Reply #4 on:** September 13, 2016, 05:45:20 PM »

Thanks Disco for your nice clear picture and shedding some light on the subject. Considering this gusset is directly under the cam gear on the crankshaft, I believe it's function is to act as an impingement baffle for oil thrown off the cam chain as it comes around. This would keep more oil in the sump area of the crankshaft versus throwing it rearwards to the transmission. This is the best theory that I can come up with. I didn't notice how close the cam chain comes to the top edge of the gusset/baffle but my guess is it's rather close clearance. Thus, a loose or worn cam chain may impact and break the corner off. This is something I will take a close look at on final assembly.

strynboen · « **Reply #5 on:** September 14, 2016, 04:13:00 AM »

it can be a suport for the casting Work..to hold the bearing Tower,,as it been casted." a mold Tool"..they are often not symentric..so the others tovers dont have them

rotortiller · « **Reply #6 on:** September 14, 2016, 04:29:07 AM »

Why not simply fix it with a repair or mod? When in doubt go with original design feature.

rt

SKOL · « **Reply #7 on:** September 15, 2016, 06:31:56 AM »

I too am curious about this... I have my cases split at the moment and found the same problem. My first thought was support, but its wayy to thin to provide any structural support. Then I thought maybe its used to keep oil towards front and stop the chain from whipping more oil back towards the transmission, but it being such a small piece I can't image it being that significant of a difference. I really don't know, but currently I have not fixed it but will need to know what I should do before I reassemble these cases.

flybox1 · « **Reply #8 on:** September 15, 2016, 07:11:58 AM »

Quote from: rotortiller on September 13, 2016, 04:21:51 AM

Might be to distribute oil like a dam or deflector, definitely adds little reinforcing.

+1....as its right next to the primary roller.

SKOL · « **Reply #9 on:** September 15, 2016, 07:32:11 AM »

Quote from: flybox1 on September 15, 2016, 07:11:58 AM

Quote from: rotortiller on September 13, 2016, 04:21:51 AM
Might be to distribute oil like a dam or deflector, definitely adds little reinforcing.
+1....as its right next to the primary roller.

I agree. Seeing that only the top portion broke off though, do you think it would be fine to run as is? Almost 2/3 of it still remain so it would still semi-function as a dam/deflector

BRAD CHIEDUCH · « **Reply #10 on:** September 15, 2016, 04:58:10 PM »

Yesterday I stopped at a motorcycle salvage yard in my area that deals primarily with old Hondas. Out of curiosity, I looked inside an engine case for the same problem and I could see a notch slightly worn into the top of the gusset about the same width as the cam chain. So I am pretty confident the cause for this damage is impact with the cam chain. Moral of the story - don't ignore your worn out/sloppy old cam chain.

Right now I have the engine cases, cylinders, head, covers etc. out for vapor blasting. Once I get them back I am going to attempt a weld repair. I'll TIG it with 4043 filler rod and give it a little preheat first. These old castings can be a bugger to weld with the oxides and miscellaneous alloys in them but I have seen others pull off much bigger weld repairs.

SKOL · « **Reply #11 on:** September 16, 2016, 04:35:27 AM »

Yeah, I'm in the same boat with having the issue. Don't have access to a TIG though, only MIG. And I'm not going to attempt to MIG weld this. Trying to decide if adding the extra inch is really going to make a drastic different in oil dispersal. The majority of the piece on mine is still in place. About the top 1/3 broke off. It's still going to keep oil in front of it, and I'm assuming that this bike as well as other bikes who have this problem are out on the road running. I dunno. I'm on the fence. I wish someone who's had this problem and fixed it or didn't would chime in and tell us from their experience. Please keep me updated with your progress on it.

Edit: I also don't have the piece that broke off, so I'd have to make one and try to get it to match up and then pay someone with a TIG to attempt to weld it on. PITA

BRAD CHIEDUCH · « **Reply #12 on:** December 17, 2016, 03:52:53 PM »

Just to close the loop on this posting - I did a weld repair on the broken oil dam / tab and it seemed to turn out just fine.

disco · « **Reply #13 on:** December 20, 2016, 11:39:54 AM »

Nice job!

RAFster122s · « **Reply #14 on:** December 21, 2016, 02:37:51 AM »

Sometimes preheating cases needing welding and wiping them down good several times with acetome can yield metal without as much impurity to pollute the welds. The cases being fairly porous... So, I have read. Some people have used Glyptal on the case internals for its oil shedding properties as well as its other advantages. Cures the porosity question for one...
Those frequent residents of the high perf section can answer its merits. Eastwood sells some as does other vendors...

I have seen several case repairs of pieces like this in addition to bosses broken or sheared off since becoming a member...

David

BRAD CHIEDUCH · « **Reply #15 on:** December 21, 2016, 05:56:56 PM »

Preheating the engine cases to approximately 200F prior to welding is required to take the chill out of the casting and not to remove alloy contaminants in the aluminum. Failing to preheat can cause the weld metal to crack.

I'm not sure what porosity question RAF is raising in this thread or how it relates to the weld repair that was conducted?? If glyptal is being proposed as a solution for weld porosity - simply it is not. Glyptal reportedly can be used to address oil drainback or windage problems but I have never encountered such problems on these bikes. However, glyptal does have its merits if used on steel or cast iron housings to prevent corrosion. If you are so inclined to apply glytal (not sure why), surface preparation and curing is imperative to achieve proper bond strength. Failing this you may be introducing other problems associated with pieces of glyptal floating around in your oil. Lastly, do not cure glyptal in your household oven as the gases being driven off during curing are rather nasty and if your wifes cooking is terrible it is about to get a whole lot worse.

RAFster122s · « **Reply #16 on:** December 21, 2016, 08:36:44 PM »

The glyptal isn't for welding but to increase the oil drainback. I do not know if the oil porosity is enough to worry about but cleaning well after heating is needed to help get any oil or other surface contaminates that come out of the aluminum. You can build a curing oven capable of handling the 200F temps out of 1" thick blue foam and several 100w incadescent light bulbs with a thermometer to monitor the heat. Guys build curing ovens for epoxy composite fiberglass or kevlar or carbon fiber composites. Even when using vacuum bagging setups. Some epoxies require or are strengthened by curing at elevated temp.

A heat gun can be used through a hole in the foam box to bring it up to temp quickly or boost the temp. Even a cardboard box could be used but the convection losses would be very high, taking more energy. Guys doing it for composite layups often buy thermoswitches to control the over temp or undertemp control of the heating source. Typically it is merely to control over temp as the number of bulbs and wattage control the upper range of temps. Cardboard or foam sheets are not at risk of fire as long as they are not in direct contact.

BRAD CHIEDUCH · « **Reply #17 on:** December 22, 2016, 05:40:54 AM »

Oil coming from pores in the aluminum while welding and thus necessitating postweld heating to remove contamination is a new one for me. Firstly, for TIG welding to be successful everything must be clean, clean, clean before you even attempt to start welding. If oil is leaching out of the aluminum while welding it would be virtually impossible to weld. There is no need for postweld heating to remove contaminants. Any oxides or scale formed from the welding process can simply be removed by grinding, sanding, or other mechanical methods.

Further, if one did entertain heating after welding (most laughable), exactly what contaminants are you going to remove at 200F - oil and grease isn't even going to start to smoke at these temperatures and certainly isn't going to remove oxides formed while welding.

HondaMan · « **Reply #18 on:** December 22, 2016, 05:03:55 PM »

Are you referring to the cam chain's anti-slip lip? This is a little casting lip that helps keep the cam chain from slipping (jumping time) when the engine is severely decelerated with a loose cam chain. You'll see them broken, or at least grooved, in many of these engines, especially if the engine was not particularly maintained. I have had them welded back in, or re-created, from time-to-time. If someone installed a "super duty" cam chain (thankfully these are gone now, was in the 1990s) with its excessively wider sideplates, the lip can be found in many little pieces in that area, the first time someone "power-shifted" the engine near redline. This causes the slack in the chain, which is greatest at redline when the middle of the cam is being pulled low to the crankshaft, to ripple to the front momentarily and hit the lip when it reaches the bottom.

BRAD CHIEDUCH · « **Reply #19 on:** December 22, 2016, 06:56:57 PM »

Hondaman,

So far on this thread we have all been speculating exactly what the real purpose is for this tab/gusset/baffle/lip - thanks greatly for your insight! I agree 100% that the damage is created by the cam chain and I have seen similar wear or notching patterns as you have mentioned but never would I have guessed that the primary intent for this piece was to keep the cam chain from slipping ... go figure. It still strikes me as a bit of a flawed design and Honda had to realize if the cam chain comes in contact that wear or irreversible damage would occur. However, one might argue that without the anti-slip lip (as you describe) damage to engine internals could be a lot worse if the chain skips a cog or two.

Regardless, case closed, mystery solved!

HondaMan · « **Reply #20 on:** December 22, 2016, 07:21:36 PM »

Quote from: speedwobl on December 22, 2016, 06:56:57 PM

Hondaman,

So far on this thread we have all been speculating exactly what the real purpose is for this tab/gusset/baffle/lip - thanks greatly for your insight! I agree 100% that the damage is created by the cam chain and I have seen similar wear or notching patterns as you have mentioned but never would I have guessed that the primary intent for this piece was to keep the cam chain from slipping ... go figure. It still strikes me as a bit of a flawed design and Honda had to realize if the cam chain comes in contact that wear or irreversible damage would occur. However, one might argue that without the anti-slip lip (as you describe) damage to engine internals could be a lot worse if the chain skips a cog or two.

Regardless, case closed, mystery solved!

This same 'lip' appeared in many of their earlier Twins, too. Rumor has it (from a friend I had who worked on Suzys) that Honda wasn't the only one to do this 'trick'.

News:

Author Topic: CB750K Engine - Broken Gusset (Read 3168 times)