Cheap eBay big bore kit or used jugs and pistons

[3Phase]

Howdy, folks!

Greg sent me a link to this thread because I'm in the middle of trying to fit a set of XJ1100 pistons/jugs to my '79 Special -- thanks, Greg, you've been a lot of help and I do appreciate it!

The XJ pistons are 3H5 ('80-'82 part number) the same as the overbore kit. I was looking the kit just yesterday on eBay, wondering if it was worth $150 to order a set and have the jugs bored out so thanks for the pictures, Marshy.

I'm still cleaning and checking the bottom end of the '79 engine and it's slow going but I'll try to speed it up a little so I can CC the head and get the piston/valve measurements!

[tw1980]

Hurry it up 3phase we're tired of waiting on you.LOL It looks to me like the cuts in the pistons are deeper than my Wysco 10.5 to 1's.I wish I could have got this $150 kit 4 years ago!At any rate for the price it seems worth a try even if it explodes.Good luck Scott!! terry

[WMarshy]

Howdy, folks!

Greg sent me a link to this thread because I'm in the middle of trying to fit a set of XJ1100 pistons/jugs to my '79 Special -- thanks, Greg, you've been a lot of help and I do appreciate it!

The XJ pistons are 3H5 ('80-'82 part number) the same as the overbore kit. I was looking the kit just yesterday on eBay, wondering if it was worth $150 to order a set and have the jugs bored out so thanks for the pictures, Marshy.

I'm still cleaning and checking the bottom end of the '79 engine and it's slow going but I'll try to speed it up a little so I can CC the head and get the piston/valve measurements!

I have zero first hand experience in engine building but have read enough where I thought the it is good practice to bore the jug to match the pistons... is that what you did..? Also, you said you are going to cc the head, that will give you the final compression ratio but what about claying the pistons to check valve to piston gap...do you plan to do that?

[3Phase]

Marshy,

The CC check is to find and then, if necessary, match the displacement in each combustion chamber. With the tolerances Yamaha used it's probably complete overkill but it's always nice to know the numbers and the cylinder head's already off the engine so I might as well check it.


At this time I don't have to bore the cylinders to match the head. Right now I'm using the cylinders and pistons from the wrecked XJ11 that I bought and they physically fit the '79 case and the '79 cylinder head. I just have to make sure the pistons will clear the valves so, yes, I'll have to use clay to do the measurements.

The problem is that I can't do that until the bottom end is cleaned and reassembled but I only have about 1 1/2 arms after my back popped. The bottom line is that I've lost some fine motor control in my left hand and I'm left-handed. It's part physical and part motivation for me but I'll try to get this done A.S.A.P.

[BA80]

Any progress on this Scott? I've been eyeballing this BB kit too.

[3Phase]

Greg, I've been thinking about getting one of the kits just for grins and if it doesn't work then it's no big deal. The re-ring on my '80G is starting to show its age after only 70,000 miles and I'm shocked -- SHOCKED! I tell you! that it'll have to be bored out this time!

I haven't been able to check the valve clearance on the '79 engine yet (or do much of anything, really) and I've put the project on slow-cook while I try to figure out how to work and ride all over again. I will get to it, it's just going to take a while.

[jwhughes3]

Good to see you back online Scott.

John

[3Phase]

Good to see you back online Scott.

John

Thanks, John, it's a slow process getting back into doing stuff that, well, "hurts when I do that!" So I stopped doing that.

[je2wheeler]

More give for the overbore

[QUOTE=crazy steve;381225]Keep in mind you'll have the expense of having the cylinders bored for that kit, so add another $100 give or take to it's cost.

An 1178 overbore will require the boring bar to make three or more passes on each cyclinder, a bunch of materal to remove. Most machine shops will charge $25 per hole per pass. Just be ready for a sizeable bill.

[jjz28]

I had my 350 chevy bored for 80 bucks, $10 a hole, I guess motorcycles cost more. This was back in '97 though. Has TC ever said what power difference he saw with his big bore? I am sure he has just havent seen it but would like to know the "seat of the pants" power increase.

[TopCatGr58]

Hey Jeff,

My "seat" lost it's memory a few decades ago! My bike had died in '92(2nd gear and 1st gear issue), parked it for 9 years, then rebuilt it, and then just rode it locally for the first year during/after breakin. But it did/does feel stronger than what I can remember, but I had/have one of the detuned 81SH's, so I may have just gotten back close to the OEM 78E power range or maybe a tad more, but don't really know. I ran it on a Dyno shortly after it was broken in, but it possibly could have used another main jet size up according to the results, but they were not much stronger/better than some well tuned OEM XS11's. 79cc's more can give you a little boost, but just a little. Some folks might get more with the larger bore...1196!?

T.C.

[trbig]

[QUOTE=je2wheeler;392510]

Keep in mind you'll have the expense of having the cylinders bored for that kit, so add another $100 give or take to it's cost.

An 1178 overbore will require the boring bar to make three or more passes on each cyclinder, a bunch of materal to remove. Most machine shops will charge $25 per hole per pass. Just be ready for a sizeable bill.

I've had my machinist do several of them now. With as exacting as the process is, and taking it to someone who really knows what they are doing (And take into account that the bottom of the bore can become larger due to heat expansion of the bit as it cuts) it runs @ $50 per hole here for a total of $200. You could maybe find someone to do it cheaper, but you want experience, not someone experimenting with "an old rice burner engine that doesn't matter if they screw it up." And yes, there's several out there with that attitude.

[cowlkilla]

I don't think it will be a problem. I have been in a discussion (sort of) with anothe

Hello all im new to the forum, well as a member. I've been useing this forum while i was building my 79 XS1100 cafe racer and found all the members knowledge useful. and know its done Im considering tearing it apart again and doing a big bore kit. i just wanted to ask if BA80, do you know for sure that this 80-81 big bore kit will work on our 79s?

[Bonz]

Any more input if that $150 kit is a viable option? Still see them on ebay.

[BA80]

Bigfoot bought one and he says that it looks just fine. I don't see any difference in this one and the expensive one except the brand name and I believe the inexpensive kit has cast pistons rather than forged. The pistons that come stock in these engines are cast and work just fine.