Author Topic: Engine done about 1800 miles since rebuild  (Read 4472 times)

Offline bikerboy

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Engine done about 1800 miles since rebuild
« on: 09.03. 2015 01:54 »
I mentioned this damned bike a year or so back and it is still giving me grief.

Its a 650 SR with 357 cam and it has twin carbs. When I built it I had everything done. Crank ground new big ends new mains new bush new guides new valves new rings the list is endless. It was resleeved and had new rings but the pistons (genuine hepolite) were reusable so I used them. Gapped the rings etc it has plenty of compression, to be honest its hard work to kick over.

It pours smoke out mainly on the left side but some from the right and you can smell the oil a mile away. It goes fine never misses pulls well etc just this damned smoke. Could it be something stupid before I pull the damned thing apart again?

I am using straight 40 oil.

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Re: Engine done about 1800 miles since rebuild
« Reply #1 on: 09.03. 2015 02:09 »

 When I did mine, my mate said to wash the bores with soapy water and wipe it clean until no more black came off on a white rag, otherwise it'll smoke like buggery...so I did and it's not too bad- just a puff of smoke occasionally, but I think that's mixture issue...did you do that?
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Offline kiwipom

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Re: Engine done about 1800 miles since rebuild
« Reply #2 on: 09.03. 2015 03:41 »
hi guys, it sounds like `rings 'or `valve guides` to me, if it has plenty of compression i would attack the guides first maybe some valve stem rubber caps, cheers 
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Offline wilko

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Re: Engine done about 1800 miles since rebuild
« Reply #3 on: 09.03. 2015 05:48 »
 Valve guides? Fair crack o the whip! They hardly get any oil as it is. They aren't OHC engines with cams flooded with oil.Wet sumping, glazed bores, stuck rings, or broken rings.

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Re: Engine done about 1800 miles since rebuild
« Reply #4 on: 09.03. 2015 06:31 »
before stripping I suggest you check the oil seal is still in place on the drive side crankshaft, it can pop out if you get excess crankcase pressure, also better check that the timed crankcase breather is workjng as it should. A mates bike had similar symptoms due to a non functioning bunn breather, which went away after he reverted to the standard breather.
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Online bsa-bill

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Re: Engine done about 1800 miles since rebuild
« Reply #5 on: 09.03. 2015 08:50 »
Quote
Valve guides? Fair crack o the whip! They hardly get any oil as it is.

well not a lot but enough obviously.
what oil gets up there has to get out again, so drain holes  need to be clear, mine were certainly not, really needs barrels off though - sorry
All the best - Bill
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Online Triton Thrasher

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Re: Engine done about 1800 miles since rebuild
« Reply #6 on: 09.03. 2015 17:31 »
How long does a pint of oil last?

Online muskrat

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Re: Engine done about 1800 miles since rebuild
« Reply #7 on: 09.03. 2015 19:07 »
G'day bikerboy. Do a compression test, hold throttle wide open and at least 10 kicks per side. I'd guess you broke a ring on assembly. Get a hold of a video endoscope and check the bore for scores. https://www.youtube.com/watch?v=LgbhePnUHiI
Cheers
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Offline bikerboy

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Re: Engine done about 1800 miles since rebuild
« Reply #8 on: 10.03. 2015 23:44 »
Sorry to disappoint but 4 new valve guides when building new valves fitted new springs and the valves were cut by an engineering company not ground in. Parts from TMS in Nottingham so a renouned dealer not ebay specials.

Have had bores off to check rings and checked the ring gaps YET AGAIN :(

As I said there was no expense spared when I put this damned thing together about the only thing that was not stripped and totally rebuilt was the gearbox.

As for oil use lets just say I have to put a pint in every time I use it.

Compression test fine and repeated 3 times and I have already stuck an endescope down the bore no signs of any scores or marks. :(

I am totally baffled by it I have had the top end off once since the rebuild to check rings etc.

Mind you the good news is that it goes like shit off a shovel and not much overtakes me because they dont want to plough their way thru the smoke :)

Offline kiwipom

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Re: Engine done about 1800 miles since rebuild
« Reply #9 on: 11.03. 2015 07:20 »
hi guys, bikerboy oil can only get into the combustion chamber via the valve guides or up past the rings unless you have a cracked head, cheers
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Online beezermacc

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Re: Engine done about 1800 miles since rebuild
« Reply #10 on: 11.03. 2015 08:22 »
A couple of things, and these are only long shots so don't get your hopes up...... maybe the sump has too much oil in so, no matter how good everything is, oil is getting forced up past the bores. Normally you would also get oil passing the timing breather I know. In fact, is the timing breather aligned properly and is the escape airway clear? Is the pump scavenging properly? If you stop the bike how much oil is in the sump? (do you have a drain plug on your sump plate - makes life easier). Have you got the correct banjo bolts on the rocker feed pipes? A10 banjo bolts have very small holes whereas goldie ones have big holes so too much oil could be getting into the top end and pouring into the valve guides (unlikely but I said it was a long shot).
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Re: Engine done about 1800 miles since rebuild
« Reply #11 on: 11.03. 2015 20:44 »
You say the pistons were OK but did you check that the ring clearances in the grooves were right? Apparently too much back clearance can cause the rings to flutter and act like pumps forcing oil past them.
You've done everything else so the pistons are looking like the last resort.

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Re: Engine done about 1800 miles since rebuild
« Reply #12 on: 12.03. 2015 01:08 »
As per my earlier post on whether crankcase pressure is the cause....this can be checked without too much work, if there is pressure in the primary drive case due to a failed crankshaft seal loosening the case filler cap should show gases escaping, some caps have small holes in them to release pressure which would also show gases escaping. If you have a leaky seal around the gearbox shaft as most bikes seem to then it may be that not much pressure will build up in the case though.

A failed crankshaft seal will prevent the timed breather from doing its job.

The timed breather should have a small puffing of gas coming out, from the hole in the crankcase provided for this, more so after the first few seconds after starting, on my mates bike it would start smoking out the pipes, mainly the left, at higher speeds, at tickover it was ok, he had a special bunn breather set up which did not work. It burnt oil at an incredibly high rate like yours, but did not run well and would barely exceed 60mph.
New Zealand

1956 A10 Golden Flash EA7-168x, CA10 913x, left BSA together for Liverpool, 5th Dec 1955.

1949 B31 rigid “400cc hot rod” (favourite bike)

1949 C11 rigid, but why!!! (cos it was cheap)

1937 B21, missing parts so mission impossible?

1952 Armstrong Siddeley Whitley for rainy days (with wife).

GL1800 Goldwing not sure why, maybe cos it always starts

Offline bikerboy

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Re: Engine done about 1800 miles since rebuild
« Reply #13 on: 12.03. 2015 01:54 »
Thanks for all your replies and help this is my guesswork so far.

Possibly pistons as the rings fitted in them fine but they were pistons I had used before and never gave me a problem

Possibly the breather which I notice has been spoken about already. The guy who done the engineering work for me also botled the bottom end together and I am wondering if the crankcase breather is blocked. The oil seems to circulate fine but I have had it wet sump once and when I started it unusually it did not cover the garage floor which is suspicious. That to me would indicate a breathing problem, the bike not mine :)

The only other option is a cracked cylinder head (this head I did buy off ebay :() But as I had new valve seats made and fitted I would have expected any crack to become evident during that work or when I heated it up to fit the valve guides. I have not had the primary case off but it did have a new oil seal fitted on that side so I dont expect that to be the problem.

Looks like there is no easy fix then its take the damned thing apart again :(

The only other thing that occured to me was if the pressure relief valve was not working correctly that maybe crankcase pressure would build up then and force oil past the rings as it has nowhere else it really can go but I would have expected more signs of that and oil leaks galore which I dont have.

Thanks for all your suggestions as soon as I finish a Trident I have on the bench I will strip the damned thing down again :(

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Re: Engine done about 1800 miles since rebuild
« Reply #14 on: 12.03. 2015 04:22 »
the pressure relief valve will not cause excess crankcase pressure as it in the oil circuit and on most engines it only operates when the oil is cold and the pump can get to say 50 psi the rest of time it does not relieve any oil pressure as the oil pressure is always lower than say 50psi.

it is the timed breather that creates a partial vacuum in the crank case and if not working correctly can cause oil mist to get forced by the rings, I agree you would normally get gaskets leaking in this situation but if have a really good job on them and it sounds like you probably have ....they will hold up.....my mate had also fitted a new crankshaft seal but that did stop it being forced out of position after about the same miles as yours due to the excess crankcase pressure, in fact a new seal might be more prone to popping out of the case than one that been able to get well stuck in for a few years *conf*

As you can see I think it is worth eliminating as a possible cause before stripping the top end down again, unfortunately taking the primary apart can take a while as well  *conf*
New Zealand

1956 A10 Golden Flash EA7-168x, CA10 913x, left BSA together for Liverpool, 5th Dec 1955.

1949 B31 rigid “400cc hot rod” (favourite bike)

1949 C11 rigid, but why!!! (cos it was cheap)

1937 B21, missing parts so mission impossible?

1952 Armstrong Siddeley Whitley for rainy days (with wife).

GL1800 Goldwing not sure why, maybe cos it always starts