4R0 ignition swap to '79

[Dbshea]

Long story short my #3 cylinder lost about 60psi compression. Not good with XSSE around the corner. I've got a very clean, low mile 4R0 motor here ready to trade places with my stocker. (I'll tear the 79 down over winter and see what failed) my question for the collective peanut gallery:

I do have the elusive yellow sticker 4R0 ignition box, I know the wiring is the same (sans power to the now unneeded ballast resistor) as well as the coils. I've got all the correct parts, my dilemma is: do I maintain the 4R0 set up or swap my 79 advance unit over. From my minimal research I understand the yellow sticker ignitions are not easy to come by but is their failure rate enough to warrant the labor?

With a long haul like xsse on the horizon, it occurs to me that having the same ignition as my riding partner (79 sf) has the benefit of packing (and sourcing) less dissimilar parts...

[BA80]

You don't need to change the igniter, just the centrifugal advance under the left cover.

Those 81 cams will have a different timing curve than the 79 so probably an 80 mechanical unit will work best. The 81 doesn't have mechanical advance but the cams are the same as the 80.

Other than that you should be golden. That 4R0 engine will seem kinda gutless compared to the 2H7 though.

Let me know if you need a 3H7-10 unit. Pretty sure I have a couple here if I can find them.

[Dbshea]

You don't need to change the igniter, just the centrifugal advance under the left cover.

Those 81 cams will have a different timing curve than the 79 so probably an 80 mechanical unit will work best. The 81 doesn't have mechanical advance but the cams are the same as the 80.

Other than that you should be golden. That 4R0 engine will seem kinda gutless compared to the 2H7 though.

Let me know if you need a 3H7-10 unit. Pretty sure I have a couple here if I can find them.

So you are a propenent for swapping the 4r0 equipment out? Obviously easiest path forward is to simply swap the boxes so the ignitions match but if failure is a common enough occurrence then I suppose the swap is validated.

[BA80]

So you are a propenent for swapping the 4r0 equipment out? Obviously easiest path forward is to simply swap the boxes so the ignitions match but if failure is a common enough occurrence then I suppose the swap is validated.

Putting the earlier stuff on the engine would be the safest thing I think. Not sure the wiring is the same for the 4RO and the 81 uses 3 ohm coils, the 79 1.5 ohm with the ballast resistor.

Maybe some electrical guru will weigh in here but I personally would feel safer, particularly on a long trip, to match the mechanical parts rather than take a chance with fooling with the electrics.

Magic smoke is hard to come by in the middle of nowhere.

[TopCatGr58]

I agree with Greg,

Swap the timing parts, keep your 79 ignition parts the same, that way it'll be easier when you transplant the 79 engine back in. The 81 didn't have "Mechanical" centrifugal advance, but had that same curve built into the TCI, and still used the vac. advance for it's purposes. With the 79 mechanical parts, you can play with tweaking the preset advance amount a bit to see if it affects the timing of the power curve. IIRC, the "F" timing mark on the 79 indicates ~10 degrees static advance timing at ~1100 rpm. I can't find the specs on the 81 that says what it's static timing is, but the 82XJ's is only 5 degrees BTDC at ~ 1100 rpm which is 5 degrees less than the early engines. The TCI's create the same maximum 36 degrees affective centrifugal advance, and that's what the mechanical cent. adv. parts will create at the proper rpm.

And this way, you can pack just 1 79/2H7 TCI for your rally trip/group.

T.C.

[BA80]

I agree with Greg,

Swap the timing parts, keep your 79 ignition parts the same, that way it'll be easier when you transplant the 79 engine back in. The 81 didn't have "Mechanical" centrifugal advance, but had that same curve built into the TCI, and still used the vac. advance for it's purposes. With the 79 mechanical parts, you can play with tweaking the preset advance amount a bit to see if it affects the timing of the power curve. IIRC, the "F" timing mark on the 79 indicates ~10 degrees static advance timing at ~1100 rpm. I can't find the specs on the 81 that says what it's static timing is, but the 82XJ's is only 5 degrees BTDC at ~ 1100 rpm which is 5 degrees less than the early engines. The TCI's create the same maximum 36 degrees affective centrifugal advance, and that's what the mechanical cent. adv. parts will create at the proper rpm.

And this way, you can pack just 1 79/2H7 TCI for your rally trip/group.

T.C.

I would reiterate that with the 81 cams the 80 mechanical advance will need to be used to get the proper timing curve. I don't think the 79 advance unit will play well with the milder cams.

[TopCatGr58]

Hey Greg,

I think Scott/3Phase did an expose` on the different timing curves for the different model years, not sure??

SO...the milder cams can't tolerate as much advance timing as quickly, is what I think you're stating/suggesting, and so that's why changing/retarding the static timing to only 5 degrees BTDC may be all he needs to better align the timing curves to the cams?

Vs. having to put out $$ for the 80 timing parts/weights.

The diagrams I have shows that the XS(early?) model Cent. Adv. is maxed out at 36 degrees(26 +10degrees static) at 4,750 rpm, whereas the XJ(also milder cams) programmed Cent. Adv. is maxed out at 36 degrees but at 5,500 rpm...and starts with only 5 degrees static advance.

T.C.

[BA80]

Initial timing won't change the curve, just where it starts.

[3Phase]

Electrically there is no problem and any XS11/XJ11 TCI will plug into the harness without leaking smoke but as T.C. and Greg said, match the ignition advance setup to the TCI, engine and cams.

The camshafts are the same for '78 and '79 with the 2H7 cams and from '80 to '82 they all use the 1980G 3H5 cams. Crazy Steve took pictures of the three different parts for a mechanical advance interchange guide:-


XS11.com Forums > Repairs > Interchange Guide: Mechanical Advances

[Dbshea]

Initial timing won't change the curve, just where it starts.

I wish I had paid closer attention to what you were saying about the advance... Swapped over my 79 advance (which for the record is not difficult) thinking the BOX I needed was from an 80. Wrong. Needless to say, this was an exercise in futility. I'll check what's in my other donor motor for the correct advance.

[Dbshea]

Electrically there is no problem and any XS11/XJ11 TCI will plug into the harness without leaking smoke but as T.C. and Greg said, match the ignition advance setup to the TCI, engine and cams.

The camshafts are the same for '78 and '79 with the 2H7 cams and from '80 to '82 they all use the 1980G 3H5 cams. Crazy Steve took pictures of the three different parts for a mechanical advance interchange guide:-


XS11.com Forums > Repairs > Interchange Guide: Mechanical Advances

That post was actually the one I stumbled upon that clarified what Greg was saying. And it makes perfect sense, it was obtuse of me to think that the ignition box had any effect on the curve. I had 4r0 on the brain (where the curve IS controlled by the box)

So I'll be swapping out components again. However, while cleaning up the wreckage in my shop I realized I have two yellow tag ignitions. Now I'm contemplating putting the 4R0 back in and swapping the coils to 3 ohm... I'd rather not split open my parts 80 motor if I don't have to

[TopCatGr58]

Initial timing won't change the curve, just where it starts.

Hey again,

That's sort of what I was hinting at, that with the 79 timing parts on the 81 engine, that he could just set the initial timing point 5 degrees retarded vs. the oem 10 degrees, so that even though the 79 cent. adv. comes on a little earlier, that putting the 5 degrees retard would come "CLOSE" to matching the actual time curve of the advance for the 81 cams.

But after reading his other posts, looks like he'll be using the 4RO afterall.
Looks like we'll NEVER know now!?

T.C.

[BA80]

Hey again,

That's sort of what I was hinting at, that with the 79 timing parts on the 81 engine, that he could just set the initial timing point 5 degrees retarded vs. the oem 10 degrees, so that even though the 79 cent. adv. comes on a little earlier, that putting the 5 degrees retard would come "CLOSE" to matching the actual time curve of the advance for the 81 cams.

But after reading his other posts, looks like he'll be using the 4RO afterall.
Looks like we'll NEVER know now!?

T.C.

10º is only on the 78, 79 is 5º. Retarding the initial timing would make the total advance fall short of the 36º of total advance.

I hope that 4R0 will play well with the ballast resistor.

[TopCatGr58]

10º is only on the 78, 79 is 5º. Retarding the initial timing would make the total advance fall short of the 36º of total advance.

I hope that 4R0 will play well with the ballast resistor.

Darn, you're right, oh well, lesser of two evils, amount of work to make the swap functional with the least amount of work vs. performance results.

It doesn't need the BR, and all he has to do is make a jumper wire to plug into the harness bypassing the BR for the time being.

T.C.

[3Phase]

Db,

Which model/year wiring harness do you have on your XS?

It may not matter but you don't have to change the coils and unless the coils are bad then you should actually get better starting from the earlier coils with the external ballast resistor.

All XS11s should have a Red/Yellow ballast resistor bypass wire that's connected to a (Green?) wire on the starter motor terminal of the starter solenoid and it runs up to the TCI. Inside the TCI the circuit goes through an isolation diode and when the engine is cranking it feeds 12V out to a White/Red wire that bypasses the ballast resistor and runs directly to the ignition coils.

When you let off the Start button the the coils get their juice from the ballast resistor again and the isolation diode in the TCI keeps the ignition circuit current from backfeeding into the starter motor.

Now, I don't actually have a 1981 wiring harness or a 4R0 TCI in my hands but according to the factory '81 schematics it looks like Yamaha left in the whole ballast bypass wiring setup for the '81H and '81SH wiring harnesses.

If the '81 wiring really hasn't changed and the 4R0 TCI really does still have the internal diode to let it use the ballast bypass circuit then it's still feeding 12V directly to the coils when the engine is cranking even though the stock 1981 3 Ohm coils have no external ballast resistor to bypass.

Even if the ballast bypass circuit isn't there or doesn't work, the early-style coils should work fine with the 4R0 TCI and the 1981 wiring harness, just don't forget to use the ballast resistor or it'll be a race see if the TCI or the coils will make better toast.

.