The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: pdg on 28.10. 2014 15:29
-
I've recently acquired an A7 Star Twin that has an oily right hand exhaust (looking from the back of the bike). The plugs are clean and both look to be in the same condition. The bike has not done many miles following a complete rebuild.
There aren't any great plumes of smoke, just a gently rolling oily vapour coming out of the right hand exhaust when the engine is switched off.
Would I be right in assuming the exhaust valve guide has mysteriously given up the ghost, or could it be a breather problem?
Many thanks.
-
Hi and welcome. I like your avatar! *good3*
-
G'day pdg, *welcome* to the forum.
Yes that would be the culprit. Have the guides been replaced recently? I often have to go 1 thou bigger on the replacements. You don't say if it's a long or short stroke A7ST.
That info will cost you an introduction to us over in Bikes, Pictures & Members. *grins*
Cheers
-
G'day pdg, I reckon before you go berserk and strip the head off, give the whole exhaust a clean out- possible when the rebuild was done the oil residue which may have prompted the rebuild was overlooked..... *conf*
You have to pull them off first anyway- and clean them out anyway also.... *whistle*
-
Many thanks for your replies. A nice job for the winter!
-
*????* *????*winter- you serious ?- It only should take a short time (<two stubbies) to flush the pipes with some kind of gasso...and go for a blast, afterburners an' all.....? Then you'll know if you need all winter to do whatever...
-
.and go for a blast, afterburners an' all
Whoa that's new
-
But an interesting picture don't you think Bill regards BobH
-
Perfect topic for posting my questions
Just put new rings into bores 1.5-2 thou too big. Good and about even compression on both cylinders. I am pretty sure I'm looking at a valve-guide problem here. The black by the right exhaust port is wet oil. It seems to be just on the right but maybe the left piipe just fits better. Both plugs are sooty and look similar, but the right is a bit wetter. Is there some agreement that this is guides? If my (our?) conclusion is that it's right side only, should I bother with the left guides as well, or follow the "if it ain't broke" addage?
Richard L.
-
G'day Richard.
How many miles on the new rings?
It could be the ex guide looking at the amount around the pipe. If you have to do one, I'd do the lot.
Cheers
-
I think there are holes that allow oil to drain from the rocker box through the head and barrel back into the crankcase that can cause oil leaks like yours.......it might be worth a try to re torque the head bolts as that might stop the leak if the bolts are a bit loose.
https://www.draganfly.co.uk/index.php/accessories-a-misc/product/14132-
Shows the oil holes at the front of the head.....I think ..... *eek* its some since I've had the head off mine *good3*
-
agree with KiwiGF, it also important to make sure those drain holes are free (when you have the head off)
-
Kiwi,
It's a legitimate point. I wasn't really considering the injestion of oil past the gasket because the gasket was well-annealed and sprayed with copper sealer and the head had just been mounted and torqued evenly (I thought) at 32 ft.-lb. I'll test the torque on the exposed bolts, the problem being, if they move, it's basically a commitment to remove the rocker box and torque the rest. By then, the head might just as well come off so the gasket can be visually checked for leakage paths and the guides checked for tight.
I was thinking about just riding it and letting it spew for a few hundred miles to see if it cleared-up on its own by letting the rings seat. Wishful thinking, maybe, since my bores were basically oversized to the point of book-recommended re-bore before installing the new rings. Also, some folks (Muskrat, for example) have reported successful running on oversized bores. In any case, the whole deal started as a test to see if new rings would be enough to allow the oversized bores. It's too soon to declare failure on that front.
Richard L.
-
Bill,
That would be a big surprise/shock/embarrasment if the oil drains were blocked. You've made me think, this condition did not exist before I added an oil filter and SRM pump. Maybe I should bypass the filter and check (again) the hole sizes in the rocker feed bolts.
Richard L.
-
If it didn't do this before, then I doubt it's the drain holes unless some foreign object found it's way in there, or as you indicate over supply to the rockers, I have a filter and don't have the problem but I also don't have a SRM pump.
One filter element I bought though was too restrictive, I bought it online (it was compatible to the one I had used without problem) gave it my customary test (blew through it) and it failed so binned it.
-
It's a small thread-on automotive filter. Oil return has been strong. Now that I think about it, the filter precedes the flow to the rockers, so, if anything, there would be less oil getting there (not considering SRM pump). If it were indeed the pump, it's hard to imagine that the rocker box is getting so full as to overflow the tops of the guides. All this said (probably needlessly), if oil was entering the exhaust port only via the guides, I don't think the plugs would be so sooty and, in the case of the right side, wet.
OK, I really should get to work.
Richard L.
-
Richard, How does the engine sound when running? I ask this because I had an almost identical problem. The fault in my case was a loose valve guide. The symptoms that I had, was that once the engine had got nice and warm I could hear what I thought was a tappet rattling. The rattle was not audible until the engine reached working temperature. I checked the valve clearences several times with no effect. On removing the head the problem was masked by the fact that the guide was held firmly in place when the head casting was cold. Once a bit of heat was applied the guide dropped straight out! With regard to the sooty plugs I also had this problem. Eventually I removed the carb stripped it down and cleaned all the passages and jets first with brake cleaner, followed by cellulose thinner, and then I gave it a couple of long sessions in my ultra sonic cleaner. The plugs are no longer sooty. By the way, my ultra sonic cleaner is nothing special, it is just a small cheap super market cleaner but it did the job just fine. I used a 50/50 mixture of distilled water and industrial alcohol. I was truley amazed at just how much muck there was on what superficially looked a nice clean carb.
John
-
John,
Sounds very plausible, but it seems to me that I was getting oil at the exhaust before well heated and I can't recall a distinct change in clatter. I will clean her up then take her out with those things in mind (then I'll work on the A10).
Richard L.
-
Rings.
-
Maybe. Maybe. I just got back from a short ride with no apparent blowing of oil. I'm not getting too enthusiastic yet, but maybe it just needed time for the rings to bed in (as Muskrat was getting at). My fingers are crossed, and I ain't superstitious. Wilko, I appreciate your comment, because it does give me extra hope that it's just a case of new rings needing to get used to their new home.
]
Richard L.
-
I wasn't giving you hope. If it smokes from the start no amount of running in will stop it. Off with the head and barrels to investigate.
-
I say valve guide I had exactly the same about a year ago new guides cured it
-
I am with BikerBoy and Musky, if the rings are properly bedded down and you only have one oily pipe, the culprit is the sloppy valve guide, or a loose guide when up to operating temperature. That plug should also foul easily, or should be way more sooty then the other plug in the clean pipe side. I have the exact same problem with my 62 RGS, and to test that, hold your finger over the oil pipe return hole in the oil tank, when bike is all up to temp, and force more oil up to rockers at say 1200 rpm, for 30 or 40 seconds, and if the right pipe sends a little smoke out, you have guide problems.