18RG rebuild Q's

[tricky]

I have my 18RG apart, and I measured up the bores and pistons (89.49mm & 89.54mm). They seem to be in spec, the rings aren't broken, and the bores are round. The reason I stripped the engine down was because of low compression, oil consumption and bad blowby.

My question is:

Could the problems have been caused by the rings having never bed in properly, or are my measurements just spastic? Or is there another cause for the above symptoms?

Cheers!

[thechuckster]

measured ring end gap in the bore?
honing marks still visible in the bore?
marking on ring wear-faces?
upper ring installed the right way up?
oil-scrapper rings in good condition?
pistons still round?

".. low compression, oil consumption and bad blowby" are definitely symptoms of the rings not sealing

where did you measure the bore?

[Mr DOHC]

where did u measure the pistons

[tricky]

I measured the bore all the way down (5 measurements.), and measured it at right angles, so it's round too.

I haven't measured the ring end gap yet.

The hone marks are still quite visible.

The rest I haven't checked thus far. Shall post up results when I've done a few more measurements.

Cheers

[tricky]

where did u measure the pistons

I measured the pistons as per the 18RG green bible: perpendicular to the gudgeon pin, 14mm down from the bottom of the oil control ring. Is it worth measuring the piston at the crown?

[Mr DOHC]

no cuase it'll be 0.5mm smaller

[o_man_ra23]

Sounds like dead ring syndrome. A light hone and new rings should do the trick. How many k's since the rings were last changed?? if its a lot, could jsut be worn rings, cause the 18R bores are hard as arnie's abbs. If its not many, could quite well be rings were never bedded in properly. I prefer to use plain steel rings if you havent done anything like puttin a turbo or SC on the motor, as they will wear into the bores quicker, and wont wear the bores out. Chrome rings take a lot more wearing in, and can cause a lip on the bore if your not careful. If your running boost, the plain rings may not seal well enough if you have plenty of boost.

Cheers, Owen

[brett_celicacoupe]

definitly look at the rings.

do what "the chuckster" has already pointed out


another thing you you ensure if you put new rings in, is that you have the gaps of the rings at opposite ends. ie top ring has gap on inlet side, next ring down has gap on exhaust side, etc etc

[jeffro ra28]

failing that, If u end up buying some new rings. Get some total seals. They are actually a 2peice set per groove, alowing for no gap. 1 rail and 1 ring per groove, ofcourse the oil ring has 2 rails and an expander as usuall.
U will most likely want a to have your rings filed properly tho which can be a problem for the backyard mechanic.

Your rings may have simply lost their outer tension.

I think that blowby is a common accurance on old high KM, engines. Oil consumption may also be due to flogged out valves guides or worn out valve stem seals.

[tricky]

I'm not sure how many k's the engine has done. Probably 75-100k. I've only owned it for about 4000kms.

I checked the end gap on the upper rings. The tolerance in the green book is 0.1-0.3mm, but my old rings have an end gap between 0.508-0.635mm.. Sounds fuggered to me!

Owen, I'll be rebuilding with steel rings because I'll probably do a tougher rebuild in about a years time. I just want it running for the moment, and a fast bed in from steel rings suits me fine. My head gasket was starting to weep coolant, so I took this opportunity to get rid of the smoke and blowby at the same time.

Another question: 89.5mm pistons are 1mm O/S yes?

edit: jeff, who makes those total seal rings? As I said above, I might just stick with the steel rings on this rebuild, but next time, I'lllook into those.

My engine is chewing oil through the valve stems. three of the exhaust valve stems leak, but I'm freshening up the head too.

[brett_celicacoupe]

another mistake that can be made that might be contributing to hte oil usage thing is with the oil ring. it think its called the expander ring (that wavey oil ring), if your not carefull, it can overlap, then it cant do its job properly

[jeffro ra28]

another mistake that can be made that might be contributing to hte oil usage thing is with the oil ring. it think its called the expander ring (that wavey oil ring), if your not carefull, it can overlap, then it cant do its job properly

I think that the pattern of the wave on the expander ring is made so that it cannot overlap. I may be wrong.

[tricky]

I think that the pattern of the wave on the expander ring is made so that it cannot overlap. I may be wrong.

That is correct. The expander can't overlap unless it's broken.

[brett_celicacoupe]

That is correct. The expander can't overlap unless it's broken.

im not sure if the rings have always been overlap-proof. when i was putting my 18rg together, i was being shown/helped by a 60yr old mechanic. he just emphasised this.

but now i remember that the ring had little tabs on it so it couldnt overlap

[jeffro ra28]

Owen, I'll be rebuilding with steel rings because I'll probably do a tougher rebuild in about a years time. I just want it running for the moment, and a fast bed in from steel rings suits me fine. My head gasket was starting to weep coolant, so I took this opportunity to get rid of the smoke and blowby at the same time.

In that case i dont suggest getting total seals if your only doing a rough rebuild to get u going. Maybe for the tougher build in a years time tho!
They are rather silvery