Journals after resurfacing

The machine shop is going to take off about 5 thou. Off the lower and upper. Is this a bad idea because it will affect the journals?

 

5 thou off the upper and lower what ?

 

From where I split the cases.

 

So crankshaft main journals, right?

 

Yes. Sorry for not being clear enough.

 

I think you need to clarify further. If you've found a machine shop daft enough to machine 5 thou from both mating surfaces of a crankase I would suggest you take your cases and run a mile.
I hesitate to type what I'm really thinking, since in reallity what you have posted is so wrong surely it can't be correct?

 

That’s what I was wondering. It doesn’t seem right. I do think you understand. Is there any amount of resurfacing that involves the removal of material that would be okay?

 

I was asking him to resurface the top of the top case, where the mounting studs thread in. What I thought he said was sure and also that he could clean up the other side on his “honing table”. I was just nervous that that could also be removing material. I don’t actually know how much.

 

Why would you/he/them want to do that?

About the only surfacing that needs to be done is:

a) the cylinder head, in case of warpage past a certain amount, and/or....

b) the top of the jugs, so that you have a nice neat new surface for the head gasket to seal against. Yamaha gives no "tolerable" warpage specs for the jugs (like they do for the heads) but I think it would be safe to assume that the same type of warpage tolerances would apply to the jugs, too.


The top of the crankcase would never need surfacing, except in case of damage, which may not be able to be remedied. There's not much compression pressure to be contained in that area (unlike at the top of the jugs), it's just an area where oil may leak from, and as long a a new gasket and o-rings are used (and the head is torqued down properly), the chance of an oil leak in that area is minimal.

 

Do not remove any metal from the mating surfaces. Simple.
Why would you want to resurface the top of the crankase?

 

I had to read this several times in order to understand what I think you /your shop want to do, and if you do, you will have just so much scrap aluminum. Minimutly stated it correctly DON"T machine the mating surfaces of
the cases, there is much more going on than just the crankshaft main bearings.

 

Thanks for everyone’s response. This is my first rodeo. Right or wrong, i’m about to Cerekote the engine. There are some minor scratches in the head/jugs surfaces. Does that mean that I only want to eliminate warpage on the heads and not worry about any scratches. What is acceptable for scratches? since I need to hone… maybe oversize the sleeves, should I not ask them to clean up the head/top of the jugs at same time?

 

I think you'd better post some pictures of these 'scratches' - still not certain where the main bearing journals come into al of this given we're talking about a top-end rebuild - aren't we?

 

Thanks, Will do, after I get it back from being coated.
They are mostly subtle scratches from removing the gasket. But damn, that aluminum is soft.

 

Finally got the engine back from being coated. Looks like I’ll only resurface the headers.

What is the best way to get the surfaces, I’m not honing, to be as clean/right as I can get them.

 

The "headers" is usually term for exhaust downpipes.
The bits you need to clean are the machined surfaces - bores, top of the cylinders, underside of the cylinder head, and, what you really cocked up, the mating surfaces of the YICS ports, including the inside of the yics transfer port. You should have masked these off completely. Is that Cerakote going to stay on an unprepped surface, or come adrift and cause mayhem?
When you clean machined surfaces you need to not change or mark the surface, you just remove any unwanted "bits", or sometimes nicks to edges. Do not scrape with a chisel. I would start with some Scotchbrite, maybe 500 grit carborundum paper backed by a flat file or something to show up any high spots - this is not a beauty parade, all you need are clean flat surfaces.

 

Thanks for your reply!

Ya. They bunged the ends of the yics. I was under the impression that they knew to tape that part off when I was talking to them. I haven’t figured out what to do about that, if I can do anything. Worst case scenario I have a whole second engine that I can rob from.

 

Can you clean them with compressed air? Might work. Can you use the compressed air nozzle in the port that the YICS tool goes into?

 

Don't make this hard. Compressed air won't shift it - get a piece of steel dowel, cut. slot in the end and drop some emery tape in there. Stick the other end in your battery drill and away to go...

 

Did not realise it was that dense.