Author Topic: A7 engine rebuild - several questions  (Read 2026 times)

Offline Berni

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A7 engine rebuild - several questions
« on: 07.09. 2017 20:49 »
Hi guys,

I´m posting here in behalf of my dad regarding the engine of his A7.

Just one season, and he is in need of an engine rebuild (engine was knocking quite badly one day).

I took the engine apart for an inspection. The Conrod shells are definately worn. The timing side one was completely down to the copper (I think they were 3 material ones), had heat discoloring (green-black) and had gouges (from particles?).
Crankshaft needs to be ground and cylinders need a bore/hone.

Questions:

1. Pistons now are +60. Are there +80 available for the A7SS (are SS and std the same?). Or is it a better idea to get new liners? Are there any problems concerning the fitting of new liners?

2. Is there any explenation of why there is an oil in the primary side conrod, but not the timing side one? What is the reason for this hole? It can´t be to spray oil under the pistons, because just one of the cylinders has it?!?

3. Are there experiences regarding the longevity of the engine when fitting a real paper oilfilter and/or the SRM upgraded oilpump?

4. Is there anything special to the A7 (I´m not used to that old bikes) I sould pay attention to? I opened the sludge trap already, but it wasn´t really much in it.

I appreciate your answers.
Thanks a lot!

Germany A7SS

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Re: A7 engine rebuild - several questions
« Reply #1 on: 07.09. 2017 21:19 »
Just to check; the sludge trap is in the middle of the crankshaft, yes? If the sludge trap is blocked it can starve the primary side journal.

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A7 engine rebuild - several questions
« Reply #2 on: 07.09. 2017 22:20 »
You will get differing opinions on your questions  *smile*

1. I don't know of any problems fitting liners but I don't own an a7 only an A10, you can even rebore 1.5 mm thick liners, at least once, I've been told. On the A10 the barrel stubs get a bit thin at the bottom, so it's better to fit liners than go too big ......and that assumes you can get pistons. The A7 has quite thick stubs so I guess you are not so limited as the A10.

2. The con rod hole in one rod only is correct, and supposed to help the drive side bore. Some say it does little to help.

3. The SRM I'm sure helps, but there is not much wrong with the OEM pump, I've got a A65 pump with A10 drive on mine which gives increased flow at a fraction of the cost of the SRM one. SRM recommend NOT using a filter on their engines but I can't see how it can do any harm so I have one on the return, and it makes me feel a lot better knowing little bits of scarf are not going around my engine!

4. I'm not aware of any issues specifically related to the A7 but they are lower stressed than the A10, even so maybe you could check into whether new con rods are available for it? Billet type or steel? I'm also assuming you know the need for line boring the main journal? (But This applies to A10s as well).
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Re: A7 engine rebuild - several questions
« Reply #3 on: 07.09. 2017 22:29 »
G'day Berni.
1: I doubt you will get +80, the SS is higher comp than the std A7. Draganfly list +20 for the SS https://www.draganfly.co.uk/index.php/a65anda50/category/881-pre-unit-a-group and Feked have liners https://www.feked.com/hepolite-bsa-a7-cylinder-liner.html
2: The hole in the left rod is to promote oil flow to that side (a contentious issue).
3: I like the external oil filter on the return line. I don't have a SRM pump, I raced my A7SS for years on the std pump.
4: Sludge trap and timing side main bush are the most important. Crank endfloat also.
Cheers
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Offline rocker21

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Re: A7 engine rebuild - several questions
« Reply #4 on: 08.09. 2017 12:21 »
the small oil hole in the conrod  should point to the middle  of the engine, this is supposed to help with lubrication, if i were you i would get the big end eye capped and honed to the correct size and get the crank ground so they all fit  as they should, i am rebuilding my own A7ss engine and you really need to pay attention to very fine detail as that will make for a long lasting engine, as to rebore get another block or get it sleeved but with modern petrol don't go any higher that 8.5 to 1 pistons. you can liven them up by putting in the 357 cam  but don't use the 358 cam on the road(hard to find now) . Make sure the sludge trap is properly cleaned out in the crank and throughly clean everything before reassembly, also take off and clean the oil tank and oil lines then you can fit a filter in the return oil line and you can use a good 20-50 oil as that will take the grot away and it will get trapped in the filter, also fit a sump with the magnetic drain plug and change oil approx every 1000 miles or yearly and the engine will last for ages.

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Re: A7 engine rebuild - several questions
« Reply #5 on: 09.09. 2017 19:55 »
Make sure the sludge trap is properly cleaned out in the crank and throughly clean everything before reassembly, also take off and clean the oil tank and oil lines then you can fit a filter in the return oil line and you can use a good 20-50 oil as that will take the grot away and it will get trapped in the filter, also fit a sump with the magnetic drain plug and change oil approx every 1000 miles or yearly and the engine will last for ages.


Admins: Can this be made sticky and placed at the top of 'Engines' please. Everyone new to these bikes needs to see this!

Offline Black Sheep

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Re: A7 engine rebuild - several questions
« Reply #6 on: 11.09. 2017 10:08 »
I last has my A7 apart approx 40,000 miles ago. Bog standard, no filter, no high capacity oil pump. Oil changes from time to time. It puts up with a lot and doesn't complain. BSA got it pretty much right with the A7.
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Offline wardleybob

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Re: A7 engine rebuild - several questions
« Reply #7 on: 14.09. 2017 10:47 »
They look very worn indeed...

Offline bikerboy

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Re: A7 engine rebuild - several questions
« Reply #8 on: 25.09. 2017 01:13 »
You say "just one season" is he racing it?

How long has he had it and whats its history?

If you are saying thats one season since its last rebuild then I would be extremely worried unless of course he is racing it and going by your pic I doubt that he is

Offline cableguide

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Re: A7 engine rebuild - several questions
« Reply #9 on: 01.01. 2018 18:42 »
Agree with the the above and to emphasis one answer....even though I guess by now ur back on the road again.

Clean the oil tank and sludge trap as if ur life depends on it. Hard griitty crud lurks in the nooks and crannies of the tank..block all holes and let it soak in degreaser for a month then blast it using a commercial power wash then check and do again if necessary...the trap can be easily scraped out once dismantled.
 

Online Rex

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Re: A7 engine rebuild - several questions
« Reply #10 on: 01.01. 2018 21:25 »
the small oil hole in the conrod  should point to the middle  of the engine, this is supposed to help with lubrication,

I hope not, as I've assembled mine as per Draganfly's advice and with the oil hole facing outwards.

Online berger

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Re: A7 engine rebuild - several questions
« Reply #11 on: 01.01. 2018 22:05 »
ive seen a picture on the draganfly site some time ago and told them their picture had the drive side rod the wrong way. the hole should go towards the flywheel, mind you a few months ago they sent me set screws to fasten a flywheel onto a crank instead of toughened bolts, these set screws went back to them pretty sharpish and ime still astounded at the price they wanted. I told them the part number and they said o yes weve got those in stock , I thought great I can do the job. I would have been better off going to a B&Q bargain bucket. a flywheel spinning at the revs I give them would chew set screws up in no time

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Re: A7 engine rebuild - several questions
« Reply #12 on: 01.01. 2018 22:14 »
I made that mistake the first time I built the A7 plunger. Thinking the hole was to squirt oil towards the drive side bearing. As far as I could tell no harm was done the next time she was down about 20 years later.  *dunno*
But that's what the book says so it was rectified then 16 years ago.
Cheers

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Online Rex

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Re: A7 engine rebuild - several questions
« Reply #13 on: 09.01. 2018 09:39 »
I don't suppose with the limited and cossetted use these old bikes get, it really matters which way around the hole goes, but pointing it "inwards" must mean that any oil is directed towards the concave face of the flywheel/crank assembly, so other than splashing it around the innards of the engine, what use it that?
At least facing "outwards" some will make it into the D/S main bearing, and that must be of some use.

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Re: A7 engine rebuild - several questions
« Reply #14 on: 09.01. 2018 15:26 »
I could be wrong I could be right, now theres a song for you. I seem to remember many moons ago that  I read somewhere bsa put the hole in the rod to help lube the drive side big end when they found it wasn't getting enough oil, not for the hole to squirt oil out to lube something else   balloooon head go back to the pub!