Author Topic: Replacing timing main  (Read 1197 times)

Offline nigeldtr

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Replacing timing main
« on: 22.09. 2009 07:23 »
I want to replace the timing side main bush over the winter period, has anyone done this in the home workshop? I would like to do it myself and not have to send the engine away, is it possible ????

Nigel

1951 Golden Flash (engine now rebuilt) 1953 M21 a pain to start and 1961 GF that is turning into a black hole!

Offline A10Boy

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Re: Replacing timing main
« Reply #1 on: 22.09. 2009 09:45 »
Yes its possible to do in a home workshop but it all depends on whether you have the correct kit and experience, I?ve just rebuilt my A10 without too much trouble.

As you know, replacing this bearing will involve a full engine strip which is a major job. While its apart the crank will need checking and maybe a regrind, the timing bush has to be line bored which is beyond the scope of a home workshop man unless you have the kit and experience, also, the crank big ends could need a regrind. The sludge trap will need cleaning and new plugs fitting.

The pistons, rings and bores should be checked and a rebore and new pistons could be necessary, or new rings minimum if the bores are ok.

At the head, valves and guides should be checked springs checked or replaced.

Its reasonably easy for the home mechanic do the strip and reassembly, but you will have to send the crankshaft, cases and possibly barrels out to a specialist engineer for their expertise.

You will need various pullers, a torque wrench, valve spring compressor, piston ring clamps and all the usual tools. But if you?ve never done an engine rebuild before, I would advise enlisting the help of a experience friend and doing it together.
Regards

Andy

1958 Super Rocket
Plus
Harley Super Glide Custom
Yam XJR 1300

Offline nigeldtr

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Re: Replacing timing main
« Reply #2 on: 22.09. 2009 10:03 »
Andy,

Thanks for info. I have a good engineering workshop lathes, mill, plenty of tools etc and have rebuilt a few engines (many years ago). Top end is good, recently rebuilt and big ends had shown no play when I did the top. Ideally, I would like to pop in a new bush, clean out the crank and replace the BE shells if needed. I don't want to send anything off as I am in Germany and more damage gets done in transport than in my hands *ex* Hoping I can get away without a crank regrind, not sure why I should need to ream the main bearing, are they normally over size, provided it goes in square, should not really be out of alignment?

Regards

Nigel
1951 Golden Flash (engine now rebuilt) 1953 M21 a pain to start and 1961 GF that is turning into a black hole!

Online groily

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Re: Replacing timing main
« Reply #3 on: 22.09. 2009 12:16 »
A lot will depend on quite what size the crank journal is and how the job was done the last time, if there was a last time. If the bush in there was made to fit a minimally-reground journal at some point it won't be a standard size; if the journal is still at maker's spec or a standard undersize, it may be worn to some degree at least. So that's the first issue to get certainty on.
Then, you have to decide what sort of bush you want of the different types available or make-able, and what approach to take to the regrind if indeed it does need one: minimum off the crank with bespoke bush, grind down to take standard undersize bush if available, etc?. And then, whatever else, you do need to have the thing bored/reamed in situ and square with the drive side bearing to ensure perfect fit, good oil pressure and long service.
There is a number of threads hereabouts on this subject, including some great pictures of reclaimed bushes posted recently by Orabanda, plus commentaries by several people who know a heck of a lot about this topic which you might find useful to look at.
If there's one job above all others that needs to be done right for a long-lived and sweet engine, I guess it's this one.
Bill

Offline A10Boy

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Re: Replacing timing main
« Reply #4 on: 22.09. 2009 13:36 »
Yup, if you dont line ream it it will fail way before its time.

In another thread, I posted info on Lead Bronze bushes which you may find of interest.
Regards

Andy

1958 Super Rocket
Plus
Harley Super Glide Custom
Yam XJR 1300

Offline nigeldtr

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Re: Replacing timing main
« Reply #5 on: 22.09. 2009 19:24 »
Guys, thanks for the replies, I have quite a few expanding reamers in the workshop (not sure if I have one to fit though) and I could turn up a bush for the drive side bearing to fit the reamer shaft which would keep it square on the timing side and genlty open the bush out if necessary, would be interested to see any pictures of the one mentioned by Richard.

I can, and probably will after stripping , send it away to be done but I simply love to have a go at fixing things myself. Part of the reason for loving these old beasts is that there were no CNC machines or digital readouts around when they where made and there is no real "rocket" science involved, just good engineering common sense!

I am probably mad to even think about doing this but I can dream a bit.

Nigel
1951 Golden Flash (engine now rebuilt) 1953 M21 a pain to start and 1961 GF that is turning into a black hole!

Offline coater87

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Re: Replacing timing main
« Reply #6 on: 23.09. 2009 00:51 »
 Nigel,

 I will try this, but no quarentees.   http://www.a7a10.net/forum/index.php?topic=1417.msg9939#msg9939


 Lee
Central Wisconsin in the U.S.

Offline nigeldtr

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Re: Replacing timing main
« Reply #7 on: 23.09. 2009 19:52 »
Lee,

Thanks for this, I will pick on te other thread!

Nigel
1951 Golden Flash (engine now rebuilt) 1953 M21 a pain to start and 1961 GF that is turning into a black hole!