Topic: Guidance needed: Engine seized up, third piston stuck, heavy wear on the crank.

[bryanj]

Crank and rods are shot, probably pistons and bores as well

[jacquesleclochard]

Alright BryanJ, that's up for scrap. I think what I need to do now is to assess the damage, see what I can still use and plan accordingly. Could use some help. What do you think of the crankshaft and towers?

I wonder, when I look at the picture below, it is impossible for the rods to have been without oil if the pump was working.

 

[Jerry Rxman Griffin aka MuthaF'er]

Looks familiar to me. Does your crank still have all 4 oil passage stopper balls in place. I lost one and my crank/bearing pictures look like yours. Instant drop of oil pressure.

[jacquesleclochard]

Hello Jerry, what is an oil passage stopper ball? Can you show me on a scematic, so I know what to be looking for?

[Terry in Australia]

The oil stopper balls are not visible in the pic mate, they're small ball bearings set into the counterweights on your crank.

That's not the issue though, you've "cooked" your engine mate, so yep, if your oil tank was full of oil then your pump isn't working. That camshaft is dead so is your crank and crank bearings. Your cam towers don't look too bad, but if you find any deep scratches, they're toast.

If you rebuild your engine or replace it with another one, leave the rocker inspection caps out of the cam cover and make sure there is oil circulating around your head before riding it anywhere. If it's getting up into your head, it'll be getting everywhere else too. Make sure that you rebuild/replace that oil pump! Cheers, Terry.

[ekpent]

That old dry rod sure looks rusty.

[Terry in Australia]

Yeah Eric, it's gotten so hot that any oil that might have been on it has evaporated off, and it's started to rust. Cheers, Terry.

[jacquesleclochard]

YES! Lets do this! It is unfortunate that it came this far, but I have a lot of spare parts lying around. And I am motivated to do this. Will you help me out with the rebuild, Terry? I have never done this before, but it cant be that hard...

[Terry in Australia]

No worries mate, send me a return air ticket (KLM please) and fill your fridge with Heineken or Lowenbrau, and I'll be right there! Ha ha, seriously, CB750 engines aren't tricky to rebuild, main thing to remember is to keep your work area spotlessly clean, and don't cheap out, buy the following items new from CMSNL:

Pistons,
Rings,
Gudgeon pins and clips,
cam chain and tensioner assembly,
Primary chain and tensioner assembly,
Main bearings,
Conrod bearings,
New gasket set,
New engine seal set, and
Anything else that you think you'll need.

If you've got amongst your spares a good set of pistons and a good cylinder block, then just buy a new set of rings and pins and spend the money you've saved on beer. Make sure that the used parts that you use are the best parts that you have, that you have a good quality 0-20 lb ft torque wrench, and make sure you have a workshop manual sitting beside you at all times. And don't forget to have fun! Cheers, Terry.

[Jerry Rxman Griffin aka MuthaF'er]

The oil passage stopper balls in the crank seal up the drilled passageways that carry oil from the crank bearings oil passages to the rod bearings. They are press fitted then staked to hold them in place. If one comes out the oil exits that new found hole thus dropping the oil pressure throughout resulting in crank oil starvation. Not likely but I have had it happen.

[jacquesleclochard]

The oil stopper balls were all still in. Interesting little part.

So I started making up the balance today. Threw out the pistons, shafts, bearings and looked at the parts that I have. Lucky enough all engines are K6 models, that makes it easy.

Tomorrow I'll look at the heads and I will lap the valves. Also I will take a look at the crankshaft. Hondaman's manual mentiones bead blasting the camrods. Can I blast everything?

Also the kit that I will install is cruzinimg 836 kit. I already have the ape studs, the gasket set. I want to replace all the chains inside. Can I gain some on the budget to use a looped aftermarket cam chain? I know it isn't the best idea, but how bad are those chains these days?

The camchain guide and roller, what do you think? Replace?

I don't want to cut corners, but I do want to keep an eye on the expences. So if I can take some off without messing with the integrity of the engine, I should.

[bryanj]

The rubber parts should not be rock hard, if they are replace or you will get lots of broken off bits clogging your engine

[Terry in Australia]

Yeah mate, what Bryan said, he's a professional bike mechanic, and knows lots more than I do, I'm just a bum "Backyard" mechanic who's learned from making some horrific mistakes, ha ha!

I haven't read HM's book, but I've never heard of beadblasting conrods, did you mean "shot blasting"? Russ Collins (RC Engineering) shotblasted and heat treated stock conrods, and installed better bolts before Carillo's were available, and they work fine, I've got some reworked RC rods in my 836 and I regularly rev it way past redline, and I haven't busted one yet.

Z1 Enterprises sells heavy duty Tsubaki cam chains that are much stronger than standard Honda chains for under 35 bucks each, I use them in every engine I build, and love them.  http://www.z1enterprises.com/ItemDetails.aspx?itemDescription=Cam+Chain+Tsubaki+BF05M+94Link+Honda&item=TU25-9816

Cheers, Terry.

[jacquesleclochard]

Great. I found a local seller, so now I am looking at the following. 

Camchain
3 Rod bearings
10 crank bearings
Primairy chain
Roller optional
Clutch plates (see picture, they are worn)
And the shift forks.

I have 3 sets of forks here, and all are below spec. New ones are 60 euro's at cms, so expensive! My wallet opted to question said specifications...

[jacquesleclochard]

Now I took the two cranks that I have and compared the rod bearings and wear. Two come from a different crank than The one I will use. See photo. The numbers dont match. Can I still swap them?

Also my camshafts all have a different mark; R10 is the scrap one. My choices are an R1 and a R13. The 13 has a different sprocket with less teeth.

What do these prints mean?

[Jerry Rxman Griffin aka MuthaF'er]

Now I took the two cranks that I have and compared the rod bearings and wear. Two come from a different crank than The one I will use. See photo. The numbers dont match. Can I still swap them?

Also my camshafts all have a different mark; R10 is the scrap one. My choices are an R1 and a R13. The 13 has a different sprocket with less teeth.

What do these prints mean?

All those 'prints' mean is that they were not molded in the same batch. The end caps have the bearing dimensions and rod weights. Those are all that's important.

Don't worry about the 'R' stuff on the cams. Same situation. If you don't know what your cams came from use the one with the highest lobes AS LONG AS IT'S A CB750. The tooth count on the sprocket SHOULD all be the same!

[HondaMan]

So I took it apart, but not after checking the head first. When I removed the oil filter, it didn't leak a lot of oil. When I noticed this I started wondering: did the head get enough? If any? It looks like it, but still it is a bit try. Took a picture of the head.

Flipped it over and split the cases. Interesting wear on the crankshaft.  What do you think caused this?

The transmission doesn't seem to have any kind of wear, but, to be honest, I don't know what to check really. (Someone has my Hondaman book lying at home - need to get it back!)

The teeth on the primary chain gears look worn. Thoughts?

And still the pistons are seized. They should turn over now, right? If so, should I take a look at the oil pump?

Those marks on the crank weight look like the bearing size info?

[HondaMan]

Now here comes the fun part.

Third piston was stuck. The connecting rod had jammed itself. Look how dry it is.

The inner side of the piston was dry as well. The wear on the pin, is that normal?

And look at the wear at the bearings, and on the crank itself.

Well, something must have blocked the oil passage to the rod. That caused the lack of oil to the back side of the piston, because it is splashed with oil on each power stroke as the 'push' squishes to oil out of the rod bearing and then the piston runs into it on the way down. Dry rod bearing = dry piston, in just a few seconds.

[bryanj]

Somewhere on the rod, the manual tells you where, there is a weight code mark and the manual also tells you how close they have to be

[jacquesleclochard]

I did the plastigage thing. Exciting! But I forgot the manual. What am I learning from this? All the readings are the same width. The bearings that i used on the crank are the green ones, those were the ones that came with the crank.

Is this the size I should order?

[jacquesleclochard]

Now here comes the fun part.

Third piston was stuck. The connecting rod had jammed itself. Look how dry it is.

The inner side of the piston was dry as well. The wear on the pin, is that normal?

And look at the wear at the bearings, and on the crank itself.

Well, something must have blocked the oil passage to the rod. That caused the lack of oil to the back side of the piston, because it is splashed with oil on each power stroke as the 'push' squishes to oil out of the rod bearing and then the piston runs into it on the way down. Dry rod bearing = dry piston, in just a few seconds.

I cleaned all the passages. Is there a way to get behind those balls?

Your book mentions different conrod bearings. Mine dont have the holes. Could that make a difference?

[jacquesleclochard]

Somewhere on the rod, the manual tells you where, there is a weight code mark and the manual also tells you how close they have to be

Im not sure I know what you mean, Brian?

[jacquesleclochard]

Hello search function, and ohhhh boy... There is a whole new aspect of the engine right there.

[bryanj]

Find the bulletin section and look up 750/14 and 750/31. these should explain it all to you

[jacquesleclochard]

Printed it out and I am taking it to the shop. Thanks Bryan. Didn't know these existed. This is what the service guys use I take?