The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Berni on 07.09. 2017 20:49

Title: A7 engine rebuild - several questions
Post by: Berni 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!

(https://i.imgur.com/tFYle3h.jpg)
Title: Re: A7 engine rebuild - several questions
Post by: Greybeard 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.
Title: A7 engine rebuild - several questions
Post by: KiwiGF 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).
Title: Re: A7 engine rebuild - several questions
Post by: muskrat 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
kiwigf got in 1st.
Title: Re: A7 engine rebuild - several questions
Post by: rocker21 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.
Title: Re: A7 engine rebuild - several questions
Post by: Greybeard 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!
Title: Re: A7 engine rebuild - several questions
Post by: Black Sheep 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.
Title: Re: A7 engine rebuild - several questions
Post by: wardleybob on 14.09. 2017 10:47
They look very worn indeed...
Title: Re: A7 engine rebuild - several questions
Post by: bikerboy 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
Title: Re: A7 engine rebuild - several questions
Post by: cableguide 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.
 
Title: Re: A7 engine rebuild - several questions
Post by: Rex 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.
Title: Re: A7 engine rebuild - several questions
Post by: berger 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
Title: Re: A7 engine rebuild - several questions
Post by: muskrat 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

Wish this forum was around in the early eighty's.
Title: Re: A7 engine rebuild - several questions
Post by: Rex 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.
Title: Re: A7 engine rebuild - several questions
Post by: berger 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!
Title: Re: A7 engine rebuild - several questions
Post by: JulianS on 09.01. 2018 18:37
This is what BSA said about the position of the drilled rod;
Title: Re: A7 engine rebuild - several questions
Post by: berger on 09.01. 2018 20:39
well  I must have got very confused.com ,its too much abuse. thanks for clearing that one up I will sleep well tonite
Title: Re: A7 engine rebuild - several questions
Post by: Triton Thrasher on 09.01. 2018 20:48
At first glance, your dad ran the bike out of oil.
Title: Re: A7 engine rebuild - several questions
Post by: Rex on 09.01. 2018 21:20
This is what BSA said about the position of the drilled rod;

Pretty much settles that....
Title: Re: A7 engine rebuild - several questions
Post by: coater87 on 09.01. 2018 22:17
 I can maybe see this hole being of limited use on a brand new motor at high RPMs, when the clearances are still tight and the oil pump is still putting out the best it's design is capable of.

 We all have looked at the innards of these motors, and I personally believe that once a few miles have been put on and the oil is warmed up- you are not "squirting" oil out the far side rod. I think it would be a good sign if some was dribbling out of that hole.

 I could be wrong here, but I just cannot see the stated benefit of this actually working the way BSA set up the oiling system on an A series motor. *conf*

 Lee
Title: Re: A7 engine rebuild - several questions
Post by: JulianS on 09.01. 2018 22:36
The first A10 engines had identical rods, no drilling, accordingto the 1950 parts book. Move to the 1951/52 book the left rod has changed to a drilled one.

The R and R billet rods I tied and rejected some years back had 2 identical rods, no drilling, but the Thunder rods with which I replaced them came with a drilled left rod.

The early A65 lacked the hole but BSA reintroduced it after a few years, then if you look at the oil in frame A65 left rod you will see a hole each side of the rod.

So who knows?

Title: Re: A7 engine rebuild - several questions
Post by: RichardL on 10.01. 2018 12:20
I think my rods are R and R via MAP. They came with no hole. As a believer in the theory that it's there to promote oil flow, I drilled one.

Richard L.
Title: Re: A7 engine rebuild - several questions
Post by: Klaus on 10.01. 2018 16:26
All my bikes I have fit with new conrods are not drilled.
No problems if its road or race use.
Plain bearings, dont use hight pressure.
My old lathe has also plain bearings  running without any pressure, only a dippring lift some oil into the catcher.

Ok, an engine is another case ;)

but dont hype this hole.
Title: Re: A7 engine rebuild - several questions
Post by: RichardL on 10.01. 2018 18:08
Klaus,

Curious, then, about your idea (humorous or serious) as to why  BSA engineers decided to add the hole.

Richard L.
Title: Re: A7 engine rebuild - several questions
Post by: Greybeard on 10.01. 2018 19:23
Klaus,

Curious, then, about your idea (humorous or serious) as to why  BSA engineers decided to add the hole.

Richard L.
My guess, a knee jerk reaction after an engine failure during racing.
Title: Re: A7 engine rebuild - several questions
Post by: duTch on 10.01. 2018 23:27
 While rebuilding my Rockety-Flash (Rocketash?), I pondered the effect of the centrifugal action of the oil in the journals as the crank spins, but have never seen it mentioned anywhere...?

 And also maybe worth noting that the oil hole in the C-rod only aligns with the hole in the crank at 90º before& after TDC/BDC, so that's when there would be a quick squirt/s....haven't seen that mentioned either, but may be wrong on both counts ..... open slather ... *eek*



  nb -(did a typo in 'centrifugal' with a 'u' where the 'e' should be- as my old boss used to say, "it's not a stuff-up if I find it first" *smile*)-
Title: Re: A7 engine rebuild - several questions
Post by: Tomcat on 11.01. 2018 08:06
Klaus,

Curious, then, about your idea (humorous or serious) as to why  BSA engineers decided to add the hole.

Richard L.


I read somewhere long ago that when the A10 engines were first built that the left cylinder kept on seizing up. Someone in R & D said "It would be easy to diagnose if there was a window in the engine". So that's what they did, fitted perspex to the LHS of the engine and found there was insufficient lubrication to the left cylinder. And the cure was an oil hole in the LH conrod to squirt oil onto the LH cylinder.
FYI the Left hand side is AKA the Kerbside, the Nearside, the Drive side and No 1 cylinder!  *fight*
Title: Re: A7 engine rebuild - several questions
Post by: RichardL on 11.01. 2018 13:24

. And the cure was an oil hole in the LH conrod to squirt oil onto the LH cylinder.


Ah, but the hole is always pointed at the web. If anything, the oil would have to fling from the flywheel onto the cylinder wall. I'm not saying it doesn't, but I'm still on the "promote flow" bandwagon and can envision both functions. Can't imagine any spurting taking place, anyway. The hole in the rod is infrequently over the holes in the crank.

Richard L.
Title: Re: A7 engine rebuild - several questions
Post by: Johnhayesuk on 23.09. 2018 13:24
Hi guys my 1952 a7 leaks a loads of engine so here goes, I raised her up onto a makeshift table, anyone have pictures videos etc that can help me take the engine apart and rebuild with new gaskets etc anything, advice, where to purchase what not to do the bike is a real treasure that I love riding around the Malvern hills and down into wales but I’m sick of getting covered in oil and when I get back my floor is a mess too
Title: Re: A7 engine rebuild - several questions
Post by: Berni on 23.09. 2018 16:19
Hello Guys,
thanks a lot for all your information's. Now I'm meyself. The base engine is now fixed, all bearings are made, a restored cylinder with again .06 is build on, but a standard not a high compression on. Now I have again a question, can someone tell me the crankschaft degree to adjust the ignition? I want to do it with the degree disk. Someone told me 32°, but he was not sure.
Thanks again for your help.
 
Title: Re: A7 engine rebuild - several questions
Post by: berger on 23.09. 2018 19:44
I have not been to the pub, if you are not on high comp 8to1 and over I would set timing 35 degrees if over 8to 1 38 degrees
Title: Re: A7 engine rebuild - several questions
Post by: Triton Thrasher on 23.09. 2018 19:52
I have not been to the pub, if you are not on high comp 8to1 and over I would set timing 35 degrees if over 8to 1 38 degrees

As a rule, higher compression ratio requires less ignition advance.
Title: Re: A7 engine rebuild - several questions
Post by: JulianS on 23.09. 2018 20:27
The BSA Data books for 1960 and 1961 gives 35 degrees for A7 iron head 7.25:1 comp and 38 degress for A7ss 8;1 compression.
Title: Re: A7 engine rebuild - several questions
Post by: berger on 23.09. 2018 20:38
yes triton thrasher thanks for the correction , i'm going to join big jim in the pub *beer*
Title: Re: A7 engine rebuild - several questions
Post by: berger on 23.09. 2018 21:07
that's it then I will not be sticking to the rule, I will stick with what julian found *smile* *beer* *fight* *problem* *bash* *shh*
Title: Re: A7 engine rebuild - several questions
Post by: Triton Thrasher on 23.09. 2018 22:10
The BSA Data books for 1960 and 1961 gives 35 degrees for A7 iron head 7.25:1 comp and 38 degress for A7ss 8;1 compression.

Two different cylinder heads.
Title: Re: A7 engine rebuild - several questions
Post by: berger on 23.09. 2018 23:10
bloody spoil sport and I was doing so well *sad*, o well  pub tomorrow *beer* *countdown*. so what do we advise the chap 38 degrees or 35 degrees, could have 3 degrees , good singers they were *dribble*  *lol* *whistle* *good3*
Title: Re: A7 engine rebuild - several questions
Post by: edboy on 24.09. 2018 01:17
with the head off.i have always measured the bsa fraction btdc given in the manual on the compression stroke and then stamped or marked the timing side breather to a corresponding dot on the inner timing cover. not my idea but so easy to set timing again. a degree disc may be more accurate so mark it anyway.
Title: Re: A7 engine rebuild - several questions
Post by: Berni on 26.09. 2018 20:44
Hello guys,
taking in account, that I have standard pistons, instead of high compression ones, and as much as possible oversize, I will try at 35° and see what happen. In addition I can do also  do the distance measurement. If the engine "pings", hope this is the right word, I have to adjust.  *smile*
Hope to get "Maggy" back to the road.
Thanks a lot.
Berni
Title: Re: A7 engine rebuild - several questions
Post by: muskrat on 26.09. 2018 20:51
G'day Bernie.
An A7SS should be 3/8" btdc. If it pings back it off to 5/16".
Cheers