Author Topic: Switching Top Engine Cases: Does This Affect Journal Size? (Read 3101 times)

bhh1989 · « **on:** July 13, 2013, 03:14:57 PM »

So I broke out a cylinder stud down inside the thread hole of my original top engine casing on my cb750 and I am going to swap it for another spare I have in the shop. Question is, will this affect my journal sizes? i.e., do journal sizes as stamped have only to do with differences in the crank itself or can slight changes in the casing also affect size? I have a feeling it will ultimately boil down to plastiguaging to figure out but I was curious so I know a good starting point.

crazypj · « **Reply #1 on:** July 13, 2013, 03:28:44 PM »

As far as I know the cases are machined as a pair so swapping top half isn't a good idea

bhh1989 · « **Reply #2 on:** July 13, 2013, 03:31:04 PM »

Hadn't thought about them being machined together at once. Well now I am in a real pickle cause the bottom case of that top one has a broken oil filter mount.

HondaMan · « **Reply #3 on:** July 13, 2013, 04:59:08 PM »

PJ has it.

The only way 'out', if the case sizes don't match to begin with (pretty rare) is to strip the cases you will use and have them align-bored. This process involves aligning the boring bar to the largest of the 2 halves, then boring thru the smaller one. Often it also requires going to the thickest bearing shell (Black) because it is nearly impossible to just bore one half of a bearing hole.

Another method: have a new oil filter boss made up, bore the case and thread it to match the new boss. This could be a male thread on the end that goes into the case. I'd recommend also drilling a small pin hole through it, then into the case after installing this new boss, and then install a roll pin (or even threaded screw?) to ensure it won't unscrew at some future oil filter change.

754 · « **Reply #4 on:** July 13, 2013, 06:03:01 PM »

Cases are cheap for. Mid year 750,s i doubt anyone could linebore a mismatched set and fit stock bearings..and what if the trans bearings are off a bit.
Just fix one or the other.

MRieck · « **Reply #5 on:** July 14, 2013, 04:34:42 AM »

Quote from: 754 on July 13, 2013, 06:03:01 PM

Cases are cheap for. Mid year 750,s i doubt anyone could linebore a mismatched set and fit stock bearings..and what if the trans bearings are off a bit.
Just fix one or the other.

I agree...get another set

bhh1989 · « **Reply #6 on:** July 14, 2013, 01:41:00 PM »

I guess I'll be taking on that stud then. I had already taken it to a machine shop and they ended up using what tiny amount was still sticking up trying to weld a rod to it, which then broke even deeper. The remaining portion is now below the gasket surface. Any slight chance in it being ok without that stud? It's not an outer stud, I think it was for the third cylinder. I have no idea what can get this stud out, it was part of a motor that had been in the elements for over 10 years and that thing was STUCK. I even heated the casing in the oven prior to trying to extract them.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #7 on:** July 14, 2013, 02:29:17 PM »

OK then, why did they/a machine shop not try to drill it out after the ill-fated weld attempt?

754 · « **Reply #8 on:** July 14, 2013, 08:11:23 PM »

EDM machine, or tap disintegrator, can get it out....got a pic of that oil filter mount damage ?

HondaMan · « **Reply #9 on:** July 14, 2013, 08:59:58 PM »

Like Jerry ^^ said... ?

I've drilled them out with a hand drill, chipping out the threads with a pick. A few I've had to drill out oversize and helicoil back together, not hard to do.

bhh1989 · « **Reply #10 on:** July 15, 2013, 10:33:35 AM »

Quote from: HondaMan on July 14, 2013, 08:59:58 PM

Like Jerry ^^ said... ?

I've drilled them out with a hand drill, chipping out the threads with a pick. A few I've had to drill out oversize and helicoil back together, not hard to do.

Where can I find a helicoil for that size? Aren't the threads slightly different than your normal threads up top of the stud? I think I may just drill it out on my own on the press, if I can get a good dimple in the top and get it level to the press.

iron_worker · « **Reply #11 on:** July 15, 2013, 11:47:58 AM »

Set up will be important if you're trying to drill it out. You want to make sure the hole is true (square to the base gasket surface front to back and side to side).

I had a machine shop drill out a broken off stud... they charged me a crap load for setup time on the mill because they didn't both to split the cases and set up off the flat mating surface...

(Btw, the cases were empty ... just a couple bolts holding them together.)

IW

crazypj · « **Reply #12 on:** July 15, 2013, 12:05:28 PM »

Quote from: bhh1989 on July 15, 2013, 10:33:35 AM

Quote from: HondaMan on July 14, 2013, 08:59:58 PM
Like Jerry ^^ said... ?

I've drilled them out with a hand drill, chipping out the threads with a pick. A few I've had to drill out oversize and helicoil back together, not hard to do.

Where can I find a helicoil for that size? Aren't the threads slightly different than your normal threads up top of the stud? I think I may just drill it out on my own on the press, if I can get a good dimple in the top and get it level to the press.

Helicoils are not hard to find in almost any size.
I think it's a standard 8x1.25 thread, some of the single cylinder use 10x1.25 which is only slightly more difficult to find

lucky · « **Reply #13 on:** July 15, 2013, 01:19:02 PM »

Why don't you just REPAIR that broken stud? Chhhheeeeesssshhhh!

Why is it no one wants to fix anything anymore?

bhh1989 · « **Reply #14 on:** July 15, 2013, 01:40:30 PM »

Quote from: lucky on July 15, 2013, 01:19:02 PM

Why don't you just REPAIR that broken stud? Chhhheeeeesssshhhh!

Why is it no one wants to fix anything anymore?

?? I am trying to REPAIR it. Read the whole thread first.

bhh1989 · « **Reply #15 on:** July 15, 2013, 01:43:46 PM »

Quote from: Jerry Rxman Griffin on July 14, 2013, 02:29:17 PM

OK then, why did they/a machine shop not try to drill it out after the ill-fated weld attempt?

I didn't see this. I went back to the shop because they were taking forever and they showed me what they had done so far. I just picked it up and left, at that point I didn't want to pay them to keep at it and it was looking hopeless. May try another shop.

754 · « **Reply #16 on:** July 15, 2013, 03:30:22 PM »

Easiest way to hold the case level. stick a bar thru the bearing bores, v block under each end..

crazypj · « **Reply #17 on:** July 15, 2013, 03:36:53 PM »

You may find the stud is dead hard where they tried to weld bar to it and need to use a carbide burr in Dremel to get through the surface, I've had to do it multiple times on exhaust studs

bhh1989 · « **Reply #18 on:** July 15, 2013, 04:00:48 PM »

Quote from: 754 on July 15, 2013, 03:30:22 PM

Easiest way to hold the case level. stick a bar thru the bearing bores, v block under each end..

I'm bidding on some V blocks now actually, and that's a good idea. I feel like trying those extractors would be a waste of time, they always break then the hole is screwed up. Thoughts once I drill through it? Should I just go ahead and drill wide enough to get into aluminum?

HondaMan · « **Reply #19 on:** July 16, 2013, 05:02:06 PM »

Quote from: bhh1989 on July 15, 2013, 04:00:48 PM

Quote from: 754 on July 15, 2013, 03:30:22 PM
Easiest way to hold the case level. stick a bar thru the bearing bores, v block under each end..

I'm bidding on some V blocks now actually, and that's a good idea. I feel like trying those extractors would be a waste of time, they always break then the hole is screwed up. Thoughts once I drill through it? Should I just go ahead and drill wide enough to get into aluminum?

Just be careful to NOT drill through the closed bottom of the hole. In some high-perf applications where I have seen this done to get a few more threads on studs, they end up leaking oil upward from the crankcase. And, quite a bit more than you might believe! One 'fix', if this happens anyway, is to drill, tap, and setscrew the hole with a 1/8" pipe thread-type setscrew. That worked once. A Keensert went in above it.

Using Helicoils: they come in 'standard' lengths and 'long' lengths. Get the 'long' if you can. Otherwise you must install 2 'short' ones instead, which is a little tedious. Works OK, though.

bhh1989 · « **Reply #20 on:** July 17, 2013, 02:48:20 PM »

Anybody know what the exact angle the cylinders are at in comparison to the split casing? I've got it level to the drill press but still curious just in case so I can angle it exactly. I know from experience how hard it is to get a hole drilled straight down through a bolt.

bhh1989 · « **Reply #21 on:** July 17, 2013, 08:03:56 PM »

Here's a couple terrible pictures. The oil filter part is worse than I remember, the casing is cracked all around it. It seems as though the whole motor was dropped, I bought it for the top end locally. The stud drilling didn't go well at all despite perfect alignment and brand new cobalt bits. They traveled once into the stud down into aluminum, so now I have just removed the whole inside aluminum portion and will have it filled back in with weld and completely redrilled and tapped. Lots of shaping and work to do..

754 · « **Reply #22 on:** July 17, 2013, 09:40:23 PM »

I hope you welded the existing threads on the oil filter mount, before. You built up the missing area.. Really amillin machine job, and harder to fixture than the cylinder.
To re drill cylinder hole, make a Sleeve to fit in cylinder, then drill thru that, then tap.

crazypj · « **Reply #23 on:** July 18, 2013, 11:05:01 AM »

Yep, guide bushing is the way to go, but, if you can't make one, 1/8" oval carbide burr in Dremel allows you to cut the off center hole back into place

bhh1989 · « **Reply #24 on:** July 18, 2013, 11:18:24 AM »

Quote from: crazypj on July 18, 2013, 11:05:01 AM

Yep, guide bushing is the way to go, but, if you can't make one, 1/8" oval carbide burr in Dremel allows you to cut the off center hole back into place

By guide bushing do you mean something to go down into the hole that would be similar to the stud? Then build weld around that? I was just going to build up weld then redrill and tap the new aluminum.

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Author Topic: Switching Top Engine Cases: Does This Affect Journal Size? (Read 3101 times)