Seeking advise on this crankcase

Hello all,

Well the engine is now torn apart in my 83~85 barn find VF 750F, and I've discovered a bent connecting rod and some heavy stains/rust inside the cylinders.
Here are some photos.


Do you think I can get away with just some light honing and stay with existing sized pistons/rings, or do I need to bore out the cylinders? There are lots of machine shops locally who can bore this out. However, I would need to find oversized pistons / rings if I were to go that route. Where can I get oversized pistons / rings for VF 750's? I also need to get bearings / gaskets for this bike.

Can someone recommend a good parts shop?

Thank you in advance for all replies.

 

OMG that is bad corrosion! She is a bore job for sure. Not sure wher ethe pistons and rings are available but someone here will know.

Better make sure the crank, bearing journals and transmission are ok to ensure that it is worth the effort. It may be cheaper to buy a running engine and drop it in.

 

Not to be negative but you should bail oot and look for a donor engine. You will be a ton of money and time ahead when it is all set and done.

 

Hm, rust is bad, but one good thing you have is rust that is radial around the cylinder walls, that is, rust streaks are not from the top all the way to the bottom of the cylinder wall. At least this is what I can see from the pictures, maybe pictures do not show this well.
One of the cylinders has quite a bit of rust towards the top though.

I would get a good honer, ball type not a 3-prong one, and go at it. Once you break the glaze, measure the rings and ring gap inside cylinders. If it checks out, go with the honer a bit more to try to get the rust out. Once you get most of the rust, check ring gap again. If you are in spec, I would keep the crankcase, given that most of the rust is out.

If you have too much rust, and if it is too deep, you may not be able to hone it out. But I think it is worth the shot.

Note that you will always have a discoloration on the walls of cylinders, this should be OK as long as you do not have rust. Rust is what will eventually break away and leave "pockets" on the cylinder walls, and through these pockets you will loose compression.

+1 on the suggestion to check out crank and main bearings on it. If connecting rod is bad, there is a chance crank will have a crack in it too.

If rod is bent, how is head on this engine? Bent valves? Cracked heads? It takes a lot to bend a rod .....

 

TOE CUTTER is right, find a running used engine and go from there.

 

Not rebuildable IMO. That bent conrod damaged the crank and is most likely the result of a dropped valve. Most bikes in barns are there for a good reason, and your best option would be a donor engine......which you need to check carefully before purchase.

 

was in two barns today and the only thing I saw was horses, lots of horse shit too :tongue:

High-Ice-Hunchin :thumbsup:

 

I would go for a donor motor as well.

 

Many thx. Will look for a motor...

Thank you everyone for your suggestion. I will look for a donor motor...

 

Just saw this on Ebay. Honda VF750F VF750 F VF 750 84 Interceptor Engine Crank Cases Case Pistons Rings | eBay

What do you think?

Appreciate your input.

 

Cylinders look good, pistons as well. Little clean up should straighten it all out.
Just to note, you are missing connecting rods in this auction though, and a crankshaft.

 

Are donors going to be hard to find in Beijing? I really have no idea. The shipping on the eBay case is about $170 USD to China. But... you have probably already considered that, eh?

 

Nope still wouldn't touch it. Those bores would still have to be honed properly. Dingle ball or brake type 3 bar on a drill is NOT the way to hone an engine. They are just glaze breakers. Then you would need new rings. Where you going to find those?? Old/used rings on a different hone/cylinder will use oil for sure and compression would be down because they are worn in for a different surface. If it's a beater type bike it might work but won't be without problems. It would be a big crap shoot.

Then where are you going to get main/rod bearings? There are really no parts you can buy, that I know of, for rebuilding the 1st gen motors. If anybody knows where rings, bearings etc for 750/1000 engines please let me know there's a few motors I'd like to bring back alive.

 

^^^^^^^^^^^What he said^^^^^^^^^^

 

I just bought four sets of original standard sized Honda piston rings for the 1st gen motors from a shop on-line (I think they were in Georgia). They were not cheap, around US $30 X 4. I'll go there and see if they have pistons and such. Too many e-mail messages, having a heck of a time trying to find them in my inbox.


I'm not too worried about the crankshaft bearings as I can get those custom ground (grinded?) in China (did that with an EBAY BMW crankshaft for my R100/7 but that's another story...)

 

I go to LA a few times a year thus I may ship it there and bring it back in my suitcase...

 

If you can source the parts then going forward may not be so bad, I have had very poor luck finding much myself.