revtothelimit - motorbike forum

I'm seeing comments on line about not using full synth in the '83 GPz11 because:
1, It buggers the starter clutch
or
2, It causes the clutch to slip (which I know is bullshit, GPz11 uses pretty much the same clutch as the ZRX11 & ZX11)
or
3, It has a roller-bearing crank

So, over to you guys....

& before someone brings it up...

What was the question again?

Skub wrote: Wed Apr 15, 2026 8:35 pm What was the question again?

Full synth in the '83 GPz11, ok or not?

No idea. I stick fully synth in the GSXS as it's not appreciably more expensive and my thinking is it should last longer before breaking down, which considering I change the oil once a year/3k-4k miles is not really a thing, the recommended semi would be fine, but at £36 it's feck all. But then that's a modern motorcycle so no idea if any different on an old bike.

RE: asking Americans about oil. Bloody hell do they get into it. Often its a race between them as to how few miles to change it. I also notice that the same car will often have half the service intervals in the states. Doing a bit of googling seems that often this is due to the US mindset of the 50s where you changed oil every 5 mins and they can't break the cycle so manufactures just tell em to change it more, whilst telling the rest of the world another 5k is fine.

I know FA about that bike but it's 83, I'd go semi.

Surely any oil will do as long as you put a big glug of Extralube ZX1 in it

I'd not be a fan of using fully synthetic oil in older engines. Come to think of it,I've never used anything other than semi synthetic in anything,even modern bikes.


I have absolutely no scientific backing for this freely shared opinion.

Skub wrote: Thu Apr 16, 2026 9:44 am I'd not be a fan of using fully synthetic oil in older engines. Come to think of it,I've never used anything other than semi synthetic in anything,even modern bikes.


I have absolutely no scientific backing for this freely shared opinion.

I'd imagine you're Z1 is the same as recommended by Suzuki for the GSXS 10/40 semi?

I'd put what was specified in the owners manual at the time (or equivalent). Knowing you, you're changing it at least at the specified mileage/time, if not sooner so it'll be fine.

Admittedly it's not very scientific but I did an oil change on my ZX9R-E1 and put fully synth in thinking that it would be better than the semi-synth specified in the manual. The gear shift felt "off" after this and I couldn't work out why until I dropped it off for a service and the I mentioned the shift issue to the mechanic and the first thing he said was have you put fully synth in....... Correct oil put in at service and issue went away. Lesson learnt, manufacturer knows better than you.

Supermofo wrote: Thu Apr 16, 2026 10:08 am I'd imagine you're Z1 is the same as recommended by Suzuki for the GSXS 10/40 semi?

Yep. It and the filter are dumped out every 4k miles. I think the switch to synthetic goes hand in hand with longer intervals. It's something like 10k miles on my car.

Skub wrote: Thu Apr 16, 2026 11:04 am

Supermofo wrote: Thu Apr 16, 2026 10:08 am I'd imagine you're Z1 is the same as recommended by Suzuki for the GSXS 10/40 semi?

Yep. It and the filter are dumped out every 4k miles. I think the switch to synthetic goes hand in hand with longer intervals. It's something like 10k miles on my car.

Suzuki state 7500 or annually with semi, but I use fully and change 3-4k mainly as Castrol fully synth was £36 on SBS so sod all and I can't see it hurting. Oddly Suzuki state 7500 miles for the oil but only a filter every second change For another £12 sod putting fresh oil in to mix with whatever crud is lurking in the old filter.

Supermofo wrote: Thu Apr 16, 2026 11:11 am Suzuki state 7500 or annually with semi, but I use fully and change 3-4k mainly as Castrol fully synth was £36 on SBS so sod all and I can't see it hurting. Oddly Suzuki state 7500 miles for the oil but only a filter every second change For another £12 sod putting fresh oil in to mix with whatever crud is lurking in the old filter.

Aye,changing the filter at 4k or 8k will likely make no difference during your ownership. I just do it all at the same time,then I don't need to remember about the filter.

On a 80's bike I'd use semi-synth.What brand of semi-synth is another matter.I use Castrol in my Street Triple as that's what Triumph recommended.
Last time I bought some from my mates bike shop he told me that now Triumph have switched oil partners & recommend something else.It's been running on Castrol from new,it's staying on Castrol.
I might have a dilema with my SV650's,I run the old one on Castrol semi synth,but the new one that's still under warranty & gets the annual dealer service uses Motul fully synth.

Supermofo wrote: Thu Apr 16, 2026 11:11 am

Skub wrote: Thu Apr 16, 2026 11:04 am

Supermofo wrote: Thu Apr 16, 2026 10:08 am I'd imagine you're Z1 is the same as recommended by Suzuki for the GSXS 10/40 semi?

Yep. It and the filter are dumped out every 4k miles. I think the switch to synthetic goes hand in hand with longer intervals. It's something like 10k miles on my car.

Suzuki state 7500 or annually with semi, but I use fully and change 3-4k mainly as Castrol fully synth was £36 on SBS so sod all and I can't see it hurting. Oddly Suzuki state 7500 miles for the oil but only a filter every second change For another £12 sod putting fresh oil in to mix with whatever crud is lurking in the old filter.

On my SV650 the mileage for oil change intervals are 4000/ 7.500/ 11000/ 14000,but the Oil Filter change is every 11000.
Someone on one of the SV650 forum's says that,to a point,it's because the filter works better with use,similar to what happens with filtered cofee.
Unless the oil looks dirtier than usual I change my filter every other oil change,6K miles

The alleged issue seems to be that the GPz is a roller bearing engine, so use dinosaurs or semi-dino

Supermofo wrote: Thu Apr 16, 2026 7:46 am RE: asking Americans about oil. Bloody hell do they get into it. Often its a race between them as to how few miles to change it. I also notice that the same car will often have half the service intervals in the states. Doing a bit of googling seems that often this is due to the US mindset of the 50s where you changed oil every 5 mins and they can't break the cycle so manufactures just tell em to change it more, whilst telling the rest of the world another 5k is fine.

There's a known issue with Toyota recommending 10k intervals, which has lead to major sludge clogging it all up, engine failures & subsequent lawsuits*, the people changing it every 5k aren't having problems. The Explorer ST is supposed to be every 7500miles, but it gets full synth Mobil 1 every 5k.

*not sure if this is the issue with EVERY V6 Tundra being recalled for a new engine.

According to a mate in the car trade,they see lots of wagons with the top end sludged up. It seems especially prevalent among car drivers who piddle about at a maximum of 2k on the tacho. The damn things need a good thrashing at least now and again.

Long intervals between oil changes won't help sludge issues either.

The way you ride.... stick R in it.

Skub wrote: Thu Apr 16, 2026 12:38 pm According to a mate in the car trade,they see lots of wagons with the top end sludged up. It seems especially prevalent among car drivers who piddle about at a maximum of 2k on the tacho. The damn things need a good thrashing at least now and again.

Long intervals between oil changes won't help sludge issues either.

A lot of people just don't bother with services from looking at this

That video 0:) was the VW running, can't believe the residue build-up!!
The Z will be fine!!