Topic: HELP!! I Need advice -- my machinist made a mistake!!! MRieck, Hondaman

[fang]

Regarding my 900cc big bore project:
I recently had my top case half machined so my large cylinder sleeves will fit.  They fit nicely -- without studs or alignment dowels.  When I tried to put it all together last night with the dowls and studs I discovered that he machined the holes about 2mm too far forward.  They align correctly side to side, but the case's alignment dowels will not fit into the cylinders. 

I am trying to decide how serious this is before I confront my machinist with the problem. 

I imagine that it will be easy enough for him to re-machine the case so that the sleeves will fit, but the result will be oval-shaped holes for the cylinders.  My big question is WILL THIS BE BAD?  I would have liked for the sleeves to fit relatively snugly in the cases, but then again that is what the alignment dowels and big, fat, heavy-duty APE cylinder studs are for.

Just for the record, he is a reputable one-man shop.  He used to build race CB750's motors back in the day and several of the local bike dealerships trust their race bikes and drag bikes to him for all their personal and dealership-sponsored race engines, etc. 

Thanks for your feedback!

I can add some pictures if you want.  The pics are not very good -- it is hard to see what  I am talking about in the pics because the tolerance is so close...

Peace and grease
-fang

[fang]

Here is a picture.  click image to link to a significantly larger image.


The cylinders over lap in the front (on the left), and there is about 2mm of air space in the back (on the right).  The cylinders fit snugly when assembled without studs and alignment dowels.

Peace and grease
-fang

[Lumbee]

...will the cylinders fit down in the case with the studs in?  Either way I don't see how this is gonna work for you.  If the guy is as reputible and knowledgable as you say I think he will realize right off that this will not work, and redo the job.  At this point it seems to me the cylinders may be beyond repair.  If they are machined to far forward, then I don't see how that can be fixed.  Maybe you [we] are missing something.  Since this guys knows 750's bring the cases and all down to his shop and let him check it out.  Keep us updated...

[ohiocaferacer]

I'm not an expert when it comes to machining cases, but from my knowledge of building motors......i'm gonna say that upper case is gonna be ruined.

Maybe CrazyPJ can jump in on this one......he's the man when it comes to this kind of stuff.

Good luck man.......that looks bad ,
Greg

[eldar]

You can check with hondaman too, the headmaster might also be able to give some assistance.

[crazypj]

It all depends on how close to the studs the holes are going to be. if they dont get closer than 3mm your perfect, 2mm is close but useable. the case doesnt support the cylinder spigots and the extra space was deliberate so oil could get in there to cool things (doesnt that sound better than he screwed up?) Probably fitted cylinder backwards which gave the wrong offset (or does 750 have to have cylinders offset for 900cc? It wouldnt be scrap, just expensive for him to fix, the holes would have to be built up with alloy welding and remachined in the correct place
PJ

[Bodi]

I think the case body is strong enough to handle the oval shaped hole you'll end up with. Hopefully there's enough "meat" for the base gasket to seal properly. The only problem might be if the barrel holes are too close to the stud holes as crazypj noted, with aluminum you need a fair bit of metal around the threaded hole to avoid the hole distorting and letting the stud pull out.

[fang]

I believe that there is enough aluminum around the stud threads.  My main concern is the potential of having oversized oval holes, and what this will mean for the longevity of this motor

I need to know if the cases can support the cylinders if there is that much slop in there.   I am concerned that they cannot.  Remember that this is a fairly modified motor that constantly will be driven very hard.

Thanks.

[mlinder]

....Remember that this is a fairly modified motor that constantly will be driven very hard.

I think you've answered your own question. Take it back to the guy and see what he says.

[fang]

I just got off the phone with him and his first response was to somehow try to blame me for this....  How on earth can he think that?!!  I drop the parts off, explain my project, and say, "make them fit."  He says, "Yeah, sure, I've done this tons of times on old SOHC CB750's.  No problem."

I  have an appointment to come by the shop in the morning and look at the parts together.  I am only an armature machinist, but the problem seems to be fairly simple.  He failed to get the stuff aligned correctly.  While it is an easy mistake to make, it still is a mistake -- his mistake.  I only hope that he is decent enough of a fellow to make it right.

I hope this whole thing does not go sour.  And I was so happy to be developing a relationship with a skilled local machinist.

I still want your opinion about whether or not the cases are casually salvageable.

Peace and grease
-fang

[volz1fsu]

Yeah that is pretty serious.  You cant run an engine like that, he should take full responsibility for it since it is all his work.  Any machininst that doesn't stand by his work isn't worth dealing with. You'll just get burned over and over.

[fang]

OK I just got back from rechecking some stuff and I am feeling alot better about this whole thing for two reasons.

1.  I was able to verify that this is absolutely not my fault.  Here's the deal.  The machinist expressed some concerns that since he did not bore and assemble the cylinders and their big sleeves there is a possibility that they are all screwed up.  Well I did them and I know they are perfect.  (I have worked at and managed bike shops for a long time, but I no longer am in the industry...)  Anyway when I spoke with him earlier what he said basically was, "Hmmm see, I thought that those cylinders could be messed up."  Now you tell me what it would take to insert new sleeves that are almost 2mm off center.  I can't even imagine how drunk or stupid you'd have to be.   Anyway, like I said I know they are correct.  To ease my mind I just precision re-measured the work I did and it all is right on the button. 

Then I got the idea to just put a base gasket down and look at it from the inside of the motor.  Yep.  From that angle you can easily see that the sleeve holes are misaligned in relation to the studs and aligning dowels, and this visual test demonstrates that it is 100% independent of my cylinders.  SO at least this is not my fault!  That makes me feel better.
                              

2.  This whole time my big concern has been whether or not the motor will fail if the sleeves are not a snug fit into the cases, which would be the case if the machinist just makes the holes a little larger to fix this problem.  Well I just inspected one of my disassembled stock motors (one without studs or dowels in the cases or cylinders) and the cylinders are a very loose fit in the case’s holes.  SO for all of you out there who have ever wondered, on a stock motor the cylinders are NOT a snug fit in the cases.  There are several mm of free play in every direction – the dowels and studs do ALL the work of keeping everything in place.

Translation:  The machinist can just bore it a little bigger and I think everything will be OK.  There even is sufficient metal around the stud's threads in the cases, so even that is OK.  I will see if he can just make me some oval-shaped holes instead of larger round ones.

If any of you guys who are experienced at building modified motors think I might be wrong about any of this I'd really like to hear from you!!!

Thanks for all your help.  With any luck I will still have this motor assembled by the end of next week.

Peace and grease
-fang

[MRieck]

Opening the front of the case bores a little will be OK......I have seen quite a number of engine cases opened by hand to accomodate larger sleeves and they weren't to accurate in regard to the cylinder center. Generally it was done (by hand) using the new, oversize base gasket as a template. On cases that have been precision bored what is generally done id the old sleeves are pressed out and the cylinder bored for the new sleeves. Before the new sleeves are inserted the cylinder is mounted on the upper case (which is bolted onto the mill table) and bore centerline is measured for each case hole. The measurements are noted, the cylinder is  removed and the case is bored with the extra amount necessary to accomodate the sleeve. You can get case bore plates for GS and KZ engines which make the process even easier. Anyway I'm sure there is no problem with opening the front up .060 or so. I do wonder where on the case the machinist took his readings from?

[MRieck]

Those heavy duty studs will go a long way in regard to a stiff assembly too....

[Terry in Australia]

While I still wouldn't be happy that your machinist stuffed up like he did, as Mike says, overboring them again won't hurt the performance or reliability of your engine providing that the dowels are locating the cyinder block in place and you tie 'em down with those big APE studs! Cheers, Terry.

[HondaMan]

I doubt an oval hole would have any ill effect. If you have the option, see if you can find (or make) some dowels that are about .010" smaller I.D. than the stock ones, for some added stiffness against the rod offset with those big pistons. In the older 1000cc kits from the early 1970s era, I would see these lower dowels and holes get skewed after some long, hard miles, letting misalignments show up and leaks at the base cylinder become a problem. One machine shop in Illinois would deepen the holes in the cylinders (going "up" further) so they could make longer dowel tubes, then make these .010" thicker-walled ones. That seemed to fix them up better.

I have some cases from a K4 that seem OK, except where the PO broke off the top rear tube and had it rewelded back on. It looks like he dropped the engine, upside down, to crack it. I'd let them go cheap.

[fang]

MRieck, I also am interested from where on the case the machinist took his readings.  Even if all goes well tomorrow I probably will not ask him!  At the moment I just want the situation fixed while salvaging my relationship with the guy.  It is hard to find a good machinist.  He comes with high enough recommendations that I am sure he has the skills, and this is just the odd quirk – but how he handles this quirk will decide whether or not he will get the next large bundle of cash that I hope to spend on machine work.... This case boring is just a drop in the bucket.

Thanks also, HondaMan. 
I never thought of thicker dowels.  That's a great idea. 
I have several sets of spare cases here -- my K7 cases (the ones I am using) are in the best condition.  Thanks for the offer.

Peace and grease
-fang