high carbon build up

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johnwalsh
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high carbon build up

Postby johnwalsh » Sun Sep 01, 2019 4:14 pm

Not been on here for a while ( Hooray! you all say) but I have a problem with an over oiling problem ( 58 Huntmaster) which I believe is entering the combustion chamber via i/l valves. I know this seems to have been an issue with square fours and well covered on here before, has anybody found this problem with the twins. The engine has only covered about 2000 miles since a re-build with re-bore and new valves and guides. The bore seemed reasonably bedded in. There has never been an issue with blue exhaust smoke.
1958 Huntmaster
1960 Matchless G12
1958 AJS 18s

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Re: high carbon build up

Postby JohnnyBeckett » Sun Sep 01, 2019 4:34 pm

if the guides are good it mite be the head is flooding with oil and not geting to the sump quick enough or the head is geting to much oil

johnwalsh
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Re: high carbon build up

Postby johnwalsh » Sun Sep 01, 2019 9:01 pm

Thanks for the suggestion Johnny,I see no reason for flooding though as all is as standard. I am currently looking to try and fit/devise some form of valve stem seal, but thats proving rather difficult. I don't want to disturb the new guides for machining and finding something like ( umberella type ) deflector narrow enough to fit inside the inner spring just as difficult. I wondered how common a problem this was with twins.
1958 Huntmaster
1960 Matchless G12
1958 AJS 18s

keith wainwright
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Re: high carbon build up

Postby keith wainwright » Sun Sep 01, 2019 9:46 pm

Hi have you checked the head nuts for correct tork, had a problem once with oil crossing under the head gasket due to loose head nuts. Keith

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Re: high carbon build up

Postby nevhunter » Mon Sep 02, 2019 12:34 am

There's been a few previous fairly exhaustive postings on this topic. It's usually the inlet guide fit, which can be quite neat with practically no real clearance/play axially as long is it's free and has a good finish on the moving parts to reduce wear rate. The exhausts pressure acts the other way tending to put the oil back up the guide and has to run a distinct specified clearance or it may jamb and cause problems.
There's no room generally for mushroom seals and if the engine runs very hot they won't last that long. A thin stepped washer (.015" thick) Under each valve collett holder held there by the spring, can accommodate an"O" ring of a size that will stop oil going from the rocker down the stem if you care to make and fit them. (carefully) Just do the inlets. Nev

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Re: high carbon build up

Postby john.whiting » Mon Sep 02, 2019 6:54 am

The carbon may be from over rich mixture......modern petrol has lots of aromatics,polycyclics, and ring compounds that typically break down into carbon easier than 40 years ago.

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Steven.Carter
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Re: high carbon build up

Postby Steven.Carter » Mon Sep 02, 2019 12:17 pm

Tell you what you could do John, if you take the head off, turn the engine over till the pistons reach the bottom off the barrel. Then wipe clean any oil of the barrel surfaces. Now keep kicking her over for a few moments and see if any oil is getting by the rings. If there is buy yourself those IMD club pistons. All will be good after.

johnwalsh
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Re: high carbon build up

Postby johnwalsh » Mon Sep 02, 2019 3:40 pm

Thanks for all the advice chaps all taken on board. I remember you (Steve) having a similar problem and solving it with a change of pistons. Unfortunately the pistons are relatively new so I'm reluctant to change them at this stage. I have already sauced and fitted a new set of rings thinking they may be more of a problem than the recently fitted new valves and guides. I had already removed the head and barrel so didn't checked for any unswept oil, but I'll see if the change of rings will make adifference. Nev, I like the ' O ' suggestion and may give it a go.
Be a few weeks before I can update success or failure.
thanks again
1958 Huntmaster
1960 Matchless G12
1958 AJS 18s

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Steven.Carter
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Re: high carbon build up

Postby Steven.Carter » Mon Sep 02, 2019 6:00 pm

Ok John, my moneys on the rings though, if you still have some oil in the bike why not just chuck on the barrel and have a look and see

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Re: high carbon build up

Postby johnwalsh » Mon Sep 02, 2019 8:18 pm

Barrel just fitted and rings seem to make an even sweep of oil residue, no streaks, so it can only improve with time.....hopefully. I notice that the new rings appear to be cast as opposed to the previous set which I Believe were steel. That could make a difference as perhaps the previous set were not bedding in.
I liked Nev's suggestion of an 'O' ring fitted below the retaining cap, but the inner ring is a snug fit on the cap so no provision for encapsulating a washer. Research shows that Minis and MGBs got by with just an 'O' ring allowed to slide on the valve stem. I will try doing the same with Viton rings as anything else would not cope with the temperature. Just a belt and braces approach and may mean not having to dismantle the old girl again. It won't hurt . However, I believe rings were the problem and not the new valves and guides so time will tell.
thanks again
1958 Huntmaster
1960 Matchless G12
1958 AJS 18s


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