g3l compression

bombardier · Post by **bombardier** » Mon Nov 08, 2010 10:24 pm

hi all now here is a funny one i have low compression when the bike is cold,but,it is restored just after the bike has only run for around 5 minutes.i have adjusted the decompressor and the thing starts well and runs nicely,now i know some will say leave alone if not bust but i just am a little confused,oh and thanks to all who answered my previous post about fitting fork seals nice easy !!! job but well worth it.

Dick Hobart · Post by **Dick Hobart** » Mon Nov 08, 2010 10:39 pm

Are the tappets a widge too tight and when they warm up they ease off enough? I know in theory the reverse should be the case but I have come across this phenomenom before. Worth a look.

Wolseley1800 · Post by **Wolseley1800** » Tue Nov 09, 2010 5:35 pm

When you checked the compression did you do a dry and wet check.
If you do not know the difference:
Dry - as is
Wet - put a little oil in the cylinder.

If you do this when engine is cold I would not be supprised if there is a difference in reading. As you may knoe, this means you have worn rings/ bore.

Hope this helps

Groily · Post by **Groily** » Tue Nov 09, 2010 8:07 pm

AFAIK the way to test compression (if you've got anything to compare it with by way of real psi that is, and that's a whole other subject) is with engine hot - and throttle wide open. Cold and throttle shut is a different thing altogether - not much oil around the rings, and cylinder not charged.
You want the rings/bores wet with oil, the valves at clearances that are real working ones, the piston past any 'slapping' stage, the engine at operating temperature and the cylinder filled with juice/air.

More to the point, what's the oil consumption like, is the plug mucky, does it smoke? If the answers are not much, no and no then I'd leave well alone as you sort-of suggest yourself . . .

. . . unless it runs like a dog, or you already know there is a problem in the cylinder head department . . . In which latter case the remedies are the usual suspects.

Wolseley1800 · Post by **Wolseley1800** » Tue Nov 09, 2010 9:52 pm

Groily, I concure that your way of testing for a pressure is preffered but for diagnosis the way I suggest is more appropiate.

I am assuming a pressure gauge is available although you may feel the difference using the kick start.

The reason for the cold cylinder is that the problem goes away when it's warm thus suggesting something expanding. Also , no actual reference pressure is needed.

The dry test, always the first, will give a pressure.

The wet test with oil is to show wear in the piston rings or bore if there is any. The oil takes up a little of the wear causing an increase in the pressure. If there is no/ or slight increase then there is nothing to worry about. A larger increase shows wear.

The reason I suggest this test is that something is probably expanding due to increase of temperature, like the rings.

It is a simple test and does not take long.

wilko · Post by **wilko** » Tue Nov 09, 2010 11:19 pm

Wolseley1800, i see you are a masochist! Is it an auto or manual.Are we talking about the front wheel drive that is an Austin 1800 in disguise?Had to pull a few of those engines in the past. What a nightmare, it usually took all day!!Now, if it was a 6/90....

Groily · Post by **Groily** » Tue Nov 09, 2010 11:22 pm

Fair points Wolseley, thanks, and I certainly don't disagree.
Good to be able to compare the wet and dry readings without having to know what the ideal figures are. Wasn't trying to be argumentative, just wondering what the cold test would actually prove. For which fresh explanation much thanks.

Dick Hobart · Post by **Dick Hobart** » Wed Nov 10, 2010 8:32 am

Well done Wilko for lightening the tone of what's becoming a strangely heavy thread! My memories of the Wolseley 1800 go back to the mid 60's when my boss - a strangely devoted BMC freak - bought a new one. What a white elephant! If I remember rightly, apart from everything else the clutch failed at about every 4000 miles! By sheer coincidence his deputy had a much older 6/90 - a truly lovely motor and superior in every respect. Strange how both the car industry and bike industry had a habit of progressing backwards in those days!

Wolseley1800 · Post by **Wolseley1800** » Wed Nov 10, 2010 10:01 pm

Had no problems with my 1800(FWD).
It is the twin carb 'S'.
Am half way through the full restoration (5 yrs so far) but will be on road next year.

Probably the most comfortable car I have ever had. Rear leg room is 1" more than a 1970 Rolls Royce. Had a 6'6" block in front and 6'3" one in back and in comfort, no knees in back of seat. No electronics unlike the complicated modern euro boxes.

If you do a google search for Gordon Purger you will find a few pictures of it and other stuff.

Groily · Post by **Groily** » Wed Nov 10, 2010 10:14 pm

If you ever need a pair of new front hub bearings and/or a hub puller of the day Wolseley, I seem to have retained same (and maybe an oil seal or two) for a million years since I had a Land Crab way back!

Agree re comfort and space and not going into why I thought it was such an accommodating car. It just was and she'd agree.