Author Topic: Timing side main bearing  (Read 4905 times)

Offline Goldy

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Timing side main bearing
« on: 24.10. 2010 13:19 »
I have dismantled the A10 engine because not happy with the noise it;s been making. I have found that the timing side crankshaft bush is worn, and it has only done 1,000 miles since re build. I notice that both con rods have the small oil hole drilled and I know there was a discussion about this recently. So has this second hole caused a reduction in oil to the bearing?
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Offline a10gf

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Re: Timing side main bearing
« Reply #1 on: 24.10. 2010 13:55 »
Quote
and it has only done 1,000 miles since re build.
Sad. Would be very interesting to know exactly why, let us know if you investigate the history (like bad reaming angle, bad reaming diameter etc), as I am planning a new bush (have been planning for some long time now...) and want to get it right and lasting.

As for the extra oil hole, should imo not matter regarding the drive side plain bearing, should be plenty of oil pressure there, unless the oil pump\oil supply failing, oil pressure valve stuck open\weak spring. The experts here will surely come with some suggestions.

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Offline trickytree

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Re: Timing side main bearing
« Reply #2 on: 24.10. 2010 14:21 »
Doubtfull the extra con rod hole has anything to do with it as the oil has to go past the main bearing to get to the rods!

Was the bush line bored? And if so were the crankcase halves lined up correctly when the bush was bored, and lined up in exactly the same possision when the engine was assembled?
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Offline Goldy

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Re: Timing side main bearing
« Reply #3 on: 24.10. 2010 15:19 »
The guy that did the work reground the big end journals, metal sprayed the timing side journal, cleaned out the sludge trap and non return valve and hand scraped the new timing side bush (he told me that is how they did it in the 50,s) but with people talking about line boring I am begining to wonder. I am also now thinking about the quality of the bush as I do,nt know his source.
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Offline MG

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Re: Timing side main bearing
« Reply #4 on: 24.10. 2010 15:32 »
Hand-scraping main and big end bearing shells was common on large steam engines and on combustion engines with white metal bearings in the 20s, maybe still in the 30s, but then they had bearing caps with shims, so that the bearing and journal could be blue-printed, scraped and then shimmed to correct play.

I can't think of a way doing that on the A10 timing side bush and getting it halfway right. The only way to do it properly is line boring (or machining it on a large lathe), centred on the drive side bearing seat (and not on the crankcase parting line or whatever, there is absolutely no guarantee that this will align with the roller bearing!!!).
If it is made out of line or with excessive play, it will fail within very short time, also damaging the big ends by starving them of oil. If the oil system itself is okay, I'd also think it is very unlikely that the additional con-rod oil hole will cause your problems.

I'm also very sceptic about the timing side metal spraying, without successive heat treatment/hardening this is unlikely to last, if at all, especially with the harder phosphor bronze bushes and the high loading pressure on that journal. It is okay doing that on the drive side to restore a damaged roller bearing seat, but on the timing side, hmmm. If it was mine I'd rather look for a replacement crank if the journal is on the last regrind already.

Sorry to hear about the failure however!
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Online chaterlea25

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Re: Timing side main bearing
« Reply #5 on: 24.10. 2010 15:50 »
Hi Goldy,
Amen to all the other observations!
You were lucky to stop and dismantle the engine before too much other damage occured
(rod through the cases *eek*)

One or two issues not mentioned,  The oil pump???? was it overhauled or replaced?
My Brothers  A10 blew up shortly after an overhaul due to the pump body being porus and therefore not providing enough oil pressure!!

On your engine is there any signs of damage to the cam and followers?
If there is, you have suffered oil starvation because of low oil pressure
If not, the pressure release valve may be bypassing all the oil to the cam ????

HTH
John O R
1961 Super Rocket
1963 RGS (ongoing)

Offline trickytree

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Re: Timing side main bearing
« Reply #6 on: 24.10. 2010 17:09 »
There was an article in one of the classic bike comics a while ago about a well known BSA establishment that still hand scraped the main bearing bush and i couldnt believe what I had just read! There are only one reason you would do that nowadays and that is that you do not have the equipment to line bore accuratly. It was done years ago becouse the production machinery available then simply wasnt capable of working to such fine tolerances consistantly.

As for metal spraying it is most certainly an acceptable method of reclaiming worn parts, (a mate of mine metal sprays parts for Tornado fighters) but as already mentioned, correct heat treatment is an integral part of the process....find out about this first before discarding the crankshaft. If your doubious then the main journal can be ground down and a hardened sleeve shrunk fitted on (easier than heat treating the journal that way)

Im sure there was a thread recently about crancase half location....its important to get it right. My plunger cases are an excellent fit with no play at all...my A65 cases have a good 3 thou movement in them...lining them up by tapping the barrel and sump faces with a mallet is a tad agracultural in my opinion!!
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Offline Goldy

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Re: Timing side main bearing
« Reply #7 on: 24.10. 2010 17:38 »
I don,t think oil starvation is a problem as I fitted a new SRM oil pump at the same time.
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Offline MG

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Re: Timing side main bearing
« Reply #8 on: 24.10. 2010 18:05 »
The SRM pump also has it's limits and can't work wonders. Once the play in the timing side bush is big enough, the big ends won't be lubricated properly as well.
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Online chaterlea25

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Re: Timing side main bearing
« Reply #9 on: 24.10. 2010 22:07 »
Hi Goldy,
That leaves the Pressure relief valve ????
Again whats the cam and followers like ????

Cheers
John O R
1961 Super Rocket
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Offline Retired Fireman

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Re: Timing side main bearing
« Reply #10 on: 24.10. 2010 22:50 »
Hi Goldie, The bush bottom end can be made to work well believe me I built mine in 1982 and it has not had the bottom end touched since, however as members has stated here it MUST be set up properly and very few people would be capable of hand scraping the bush so it maintained it's alinement and correct clearence all over reletive to the main bear opposite. I set my bottom end up by firstly checking if the location dowels are tight when the cases are fitted together then giving the cases with a bush fitted undersized to a competent engineerring firm to first check the cylinder face for flatness then line bore the bush taking measurement from the main drive side bearing housing and finishing with proper bush/crank clearence. I used a quality NF206 C3 clearence roller on the drive side as well as fitting a modified late A65 cast iron body oil pump body with a Triumph piston type oil pressure contol valve which screws straight into the cases. The conrods have to be checked for straighness and alignment of both eyes then "closed and honed" to prove no ovality in their big end eyes by first bolting the big end caps to the rods and tightening to the correct torque (25 foot pounds from memory) then their ID must be acuratly measured and if slightly oval honed to round, if they are out more than a few thou they could have been stressed some time ago and I would not use them. To make it better have the crank "Tuftrided" or as has been discussed on here heat treated after grinding to resist wear. Of course the bush matierial must be of correct grade and that also has been discussed on the forum. As I said I did all this to my bottom end in 1982 and it has worked well over many miles ever since,  you just can't fit it together and hope it's all lined up cause if it isn't rapid wear will follow and this could be what happened to your engine.  *smile* This is how I do it and it has worked for me others could set their's up different.

Online RichardL

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Re: Timing side main bearing
« Reply #11 on: 25.10. 2010 02:59 »
goldy,

I don't recall you mentioning having taken apart the big ends. Did you? What was the condition of the bearings and journals? Were the rods stable on the big ends with no side-to-side rocking or other noticable (by hand) play? You say you didn't like the noise but you did not describe the noise. Was it a klonking or screaching? If klonking, I would think it was the big ends, perhaps with failure caused by an oversized timing-side bush. I can't say I know the hand-sraping technique, but is sounds like an opportunity for oversizing the bush and, as has been said, potentially starving the big ends. Having participated a ton in the hole-in-rod discussion and not really thinking we have yet agreed on a diffinitive answer as to the absolute reason it's there, I am, however, rather certain that the extra hole is not a cause for oil starvation at the timing-side bush (as others have unanimously said). On the other hand, if the left big end, only, was shot, it would be tempting to consider the hole in the right-side rod as a possible, maybe not probable, cause.

Richard L.
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Offline A10Boy

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Re: Timing side main bearing
« Reply #12 on: 25.10. 2010 12:31 »
Quote
hand scraped the new timing side bush (he told me that is how they did it in the 50,s)

It isnt, not on this type of bearing, its a bodge.

As has been said, the only way to go is a new Lead Bronze bush [excellent ones are made by Mike at - mike_jan@dsl.pipex.com -] You will have to tell him what internal size you want, tell him on the small side to leave plenty of meat.

Then take it to a top quality engineer, someone who's expert and knows what they're doing. I always use T&L Engineering in Bedford, www.vintage-engine.net Give Derrick the crank, cases, and bush and he will grind and line ream it properly.

I've never had any problems with his work.

Regards
Regards

Andy

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Plus
1974 Kawasaki Z1a
Yam XJR 1300

Offline Goldy

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Re: Timing side main bearing
« Reply #13 on: 25.10. 2010 14:50 »
There is no wear on the cam followers and the big end journals and shells are as new. I notice that the bearing is worn more on one side at the top it,s not equal wear all round. Reading what others have said  I  think it,s the lack of inline boring thats the problem. Obviously it is the only way to ensure correct alignment.
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Offline A10Boy

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Re: Timing side main bearing
« Reply #14 on: 25.10. 2010 15:38 »
Its a sad fact, but incorrect fitting and lack of line boring is the main cause of this failure.

Good luck.

Andy
Regards

Andy

1958 Super Rocket
Plus
1974 Kawasaki Z1a
Yam XJR 1300