14 replies to this topic

[HUBBA.HUBBA]

What's that all about? I smells slightly like exhaust fumes. Never seen it before. Is that normal?

[Guess-Works.com]

Run a compression test, but if you have fumes coming out of the breathers then it's usually to the demise of the piston rings...

[HUBBA.HUBBA]

Did a compression test last week at Smart Performance and it was about 4- 10.5, 3- 11, 2-11, 1-10.5 . I'll do another and see what it comes up with. Cheers

[HUBBA.HUBBA]

Guess Works - Done the compression test on a cold engine and it was 4= 11bar, 3=10bar, 2= 11.5bar, 1=11bar.
On the 18/8/10 it was 4=10.5, 3 =11.5, 2=11.5, 1=10.5 .To me that's not too bad, is it?

[Turbo Nick]

do another test and this time do them twice but with a squirt of oil in the bores, if the results go up significantly then it's a sign of worn bores/rings.

It doesn;t really matter too much what the actual figure the test shows is, more that they're all pretty even with each other.

[HUBBA.HUBBA]

Re did the compression test today (cold) figures were 4=10.5, 3=11, 2=11.5,1=11
with about 10cc of oil down the bore 4=14,3=14,2=15.5,1=15.5. Is that good, bad or ugly?

[AndrewJ530]

Like bud said, looks like worn rings.

EDIT: You can't be sure until you pull the head off though.

Edited by AndrewJ530, 02 September 2010 - 10:49 AM.

[pikey7]

Before you start ripping the engine apart, how many miles has it done? A slight bit of smoke from a high mileage engine is pretty much just normal wear and tear. It's not to say that the rings won't need doing in the future, but it's not something that you have to plan to do this weekend!

plus, 160psi compression on each isn't bad at all.

If it's a new engine on the other hand,then something isn't quite right.

[Turbo Nick]

i wouldn't worry too much personally, i've had to fit a catch can to mine it's chucking that much oily smoke out of the breathers now.

just start planning/saving for a rebuild at some point in the future.

[HUBBA.HUBBA]

Since it's rebore to 1293cc it's done about 3000mles. The thing is, the exhaust fumes out the back are as clean as a whistle. The only time it has shown any blue out of the back is when it was on the rolling road, whilst quickly taking the foot off the gas at 5500 rpm (a very short puff of smoke) and that was it (thought it may have been dash pot oil at the time), the compression was the same before and after that. I had the head off 500 miles ago to fit new valve stem seals (they didn't seam exactly tight on the valve) and I could not see any wear in the bores, but there was/still a bit fresh oil in the dish of pistons 4 & 3. How do you physically check the rings with just the head off? Is it possible fumes are getting up the valve stems or would the fumes not reach the crank breathers that way?

Edited by HUBBA.HUBBA, 02 September 2010 - 03:32 PM.

[bmcecosse]

You need to connect one of the breathers directly to the carb - the SU has a handy pipe on the side for this. This will take away the fumes and reduce the chance of oil leaks. The comps look good - it will be fine.

[HUBBA.HUBBA]

Thanks for that BMCECOSSE, I do have the original pipe for the flywheel side breather to the carb dangling from the canister to down under the engine and a blocked off bit of pipe at the carb. I originally unplugged from the carb as I was trying to set everything up from scrach and it seemed to work better blocked off. Will it run a little leaner with it connected?

[cooperrodeo]

The oil you see in the piston bowls is likely to be additive in the fuel and not engine oil.

[bmcecosse]

The important thing is to have the fumes sucked into the engine - at anything above idling revs it won't make any difference - just lift the idle speed slightly if need be!

[HUBBA.HUBBA]

cooperrodeo - is it still likely to be a fuel additive in just 2 bores?

bmcecosse - You are putting my mind at rest. Strangly, to be fair I'm not so worried about the effects of the fumes, more the sudden cause of them. I want to get things all tickety boo before I supercharge the beast. There are other implications as well as I may have to choose between deeeeeep dished pistons or getting the head chamber machined to reduce the compression. So if it is the rings on the way out then I am thinking change to the deep pistons.

Any more comments much appreciated

Cheers