Topic: K4 - thrown chain - hole in lower case - help finding chunk....

[ianfotheringham]

Hey there,

I just picked up a curiously unmolested very clean K3 engine, but it had once upon a time thrown a chain and has the tell tale hole just ahead of the front sprocket...the hole is about the size of a nickle, but before i clean it up and patch/JB weld it, i was wondering if anyone has experience locating possible case chunks that may or may not have fallen into the tranny case...

I cant remember from my last oil pan removal if said chunk would have ended up there or not....or if it did fall into the case, and then i flushed the hole with kerosene, where would it likely end up?


i really dont want to pull the whole works apart....


thoughts?


 

[754]

  get the crud cleaned off both sides of the case joint.. to see what is really going on..if its just that missing, easy to put a piece in there when welding

[ekpent]

Missing aluminum area looks maybe bigger that just that hole in the pic.The hole looks like a breakthrough in a larger patch. ?? Have to wonder if patched and worked on why engine is no longer in service.  Easy to pull the pan now since engine is out to take a little peek at what all might be down there. Popping off the valves cover may also give a hint to the cam condition etc also up top.

[Old Scrambler]

+1 on the advice...........a replacement lower case cover may be the best option............if the case gets repaired, you may want to invest in the steel case-guard that Honda installed on the late K0 and most K1 models. 

[lucky]

+1 on the advice...........a replacement lower case cover may be the best option............if the case gets repaired, you may want to invest in the steel case-guard that Honda installed on the late K0 and most K1 models.

There are many CB750 cases out there that are repaired and still in service.
Gt rid of that #630 chain if it is still on there.

[CycleRanger]

+1 on the advice...........a replacement lower case cover may be the best option............if the case gets repaired, you may want to invest in the steel case-guard that Honda installed on the late K0 and most K1 models.

You have to replace cases as a set. Unless you have them line-bored.

I have an engine just like that, only the hole is considerably bigger...

Finish cleaning it up around the hole, remove all that old epoxy, so you see the total extent of the damage and pull the oil pan and see what's in there.
If the hole is really only that big it can probably be patched.
Search around here, there's many threads about holed cases and repair options.

[PeWe]

I should take out the engine and diassamble it.
It might be residues/parts inside that can make real damage. Maybe time for a service anyway?
Than take the engine to people that know how to weld aluminium.

Buy a real complete gasket kit with all o-rings and rubber stuff for valve, head, oil pump with oillines that the old gasket kits did not contain.
Internal chains with tensioners, crank shaft bearings, clutch might need to be replaced....? Valve job.. just fine grinding can be done home. Another option is to buy a complete engine.
There are pople that restore engines.

Or buy an extra bike, al other parts a bonus possible to sell as parts on ebay and get some of the money back.

[lucky]

When the engine does come out. That case can be cleaned and TIG welded.
Not a problem.

Save all of these CB750 cases!!!
There are no aftermarket cases ...yet.

[ianfotheringham]

why would i want to get rid of the 630 chain? odd that i didn't even mention i have a 630...the chain that got thrown was a 530 non-oring - i heard they switched to a 630 to avoid the throwing potential...anyway, the o-ring 630 chain and sprockets i will be putting on i have far greater faith in....

+1 on the advice...........a replacement lower case cover may be the best option............if the case gets repaired, you may want to invest in the steel case-guard that Honda installed on the late K0 and most K1 models.

There are many CB750 cases out there that are repaired and still in service.
Gt rid of that #630 chain if it is still on there.

[MCRider]

why would i want to get rid of the 630 chain? odd that i didn't even mention i have a 630...the chain that got thrown was a 530 non-oring - i heard they switched to a 630 to avoid the throwing potential...anyway, the o-ring 630 chain and sprockets i will be putting on i have far greater faith in....

+1 on the advice...........a replacement lower case cover may be the best option............if the case gets repaired, you may want to invest in the steel case-guard that Honda installed on the late K0 and most K1 models.

There are many CB750 cases out there that are repaired and still in service.
Gt rid of that #630 chain if it is still on there.

The 630 chain was not OEM until 1977 or so. And while yes Honda may have wanted a stronger chain, there are dozens of models now that have way more horsepower than our CBs ever had or will have, and they run 530 chains. Running a 630 now v a good 530 is unecessary.

A 630 chain with a drop of battery acid on it will still break.

http://forums.sohc4.net/index.php?topic=102388.0

Read the first few posts.