G3 oil pump guide pin screw/body

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
tippi11
Member
Posts: 72
Joined: Sat Dec 01, 2018 9:59 pm
Location: Germany

G3 oil pump guide pin screw/body

Post by tippi11 »

I am in the process to complete my G3 which was partly restored by the previous owner. By chance I noticed that the guide pin screw does not abut against the boss (I could see about 8mm of thread). First idea was that the previous owner might have missed to screw it fully home. But the screw was quite tight, obviously tightened with a spanner. To make sure that incorrect positioning of the guide pin (collision with plunger) wasnt the reason, I unscrewed it and took the guide pin off. But surprise, surprise: Even without the guide pin it wasnt possible to screw it fully home, same result as before - about 8mm of thread visible. It would be very helpful if anybody experienced this or could give me hints, ideas solutions etc.
Thank you very much, Peter
User avatar
Pharisee
Member
Posts: 1126
Joined: Tue Mar 15, 2016 8:51 pm
Location: Lincolnshire UK
Contact:

Re: G3 oil pump guide pin screw/body

Post by Pharisee »

This is my G3 engine. The pump guide pin screw screws in fully.
NOTE.... The red fibre washer should NOT be there and was subsequently removed.
18S_2573-small.jpg
You do not have the required permissions to view the files attached to this post.
I'm from the Fens.... Gimme six.
Mick D
Posts: 2886
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: G3 oil pump guide pin screw/body

Post by Mick D »

Hi Peter

Why not compare the depth of the hole in the crank case and the length of the thread on the guide screw thread? - this should indicate whether the crank case thread is damaged or the guide screw is the incorrect length.

Does your guide screw match the design of the one shown in the manual?
Guide Pin.png
Do you have the tooling to identify the thread?

Regards Mick
You do not have the required permissions to view the files attached to this post.
SPRIDDLER
Member
Posts: 8542
Joined: Wed Sep 01, 2004 1:00 am
Location: WEST SUSSEX UK

Re: G3 oil pump guide pin screw/body

Post by SPRIDDLER »

Welcome to the Forum, Peter. :beer:

What year is your engine?
In 1947 the guide pin diameter was increased from 3/16" to 1/4".
The Guide Pin and the Guide Pin Screw (the pin holder) both have completely different part numbers to those of the earlier (pre-1947) engines.
You say it was 'partly restored' ( :? ) by the previous owner so maybe, (depending upon the year of your engine), you have the wrong Guide Pin Screw? If so, you will have the wrong Guide Pin as well.

This is the assembly for 1947 and later engines. No dimensions unfortunately but it looks longer than the screw in Mick D's photo above......
Guide pin. Oil pump (376x263).jpg
You do not have the required permissions to view the files attached to this post.
'There is a tide in the affairs of men
Which taken at the flood............'
User avatar
clive
Member
Posts: 5657
Joined: Mon Jan 01, 1990 12:00 am
Location: LONDON UK

Re: G3 oil pump guide pin screw/body

Post by clive »

Hi Peter. It would help to identify the year of your G3. And welcome.
clive
if it ain't broke don't fix
tippi11
Member
Posts: 72
Joined: Sat Dec 01, 2018 9:59 pm
Location: Germany

Re: G3 oil pump guide pin screw/body

Post by tippi11 »

Thank you all for your prompt replies.
Sorry for not providing the year, engine no as per the stamp on the crankcase is: 56/16MS28374.
I measured the diameter of the guide pin: 6.4mm (~1/4"). Guide pin screw measurements: Overall length 26mm, head height 8mm, thread length 15mm, and 3mm bare/without thread (smaller in diameter compared to thread, there is no shoulder between thread and head). Thread size, outer dia. is 9.5mm which I believe is a 3/8" thread. I dont have the tooling to verify the thread, but hopefully the 3/8" estimate is ok.

I will also try to compare the depth of the hole and the length of the thread.
Unfortunately I wasnt able to upload an image showing "my" guide pin screw so you could check the design. Any approval needed for uploads, or where is the magic button?
When looking at the above measurements, do you think I have the correct guide pin screw???
Regards, Peter
tippi11
Member
Posts: 72
Joined: Sat Dec 01, 2018 9:59 pm
Location: Germany

Re: G3 oil pump guide pin screw/body

Post by tippi11 »

Hello,
Please see image - "my" guide pin and screw/Body. Can you please check the design of the screw and let me know your comments etc.
Thank you ... :headbang:
Regards, Peter
You do not have the required permissions to view the files attached to this post.
User avatar
clive
Member
Posts: 5657
Joined: Mon Jan 01, 1990 12:00 am
Location: LONDON UK

Re: G3 oil pump guide pin screw/body

Post by clive »

Both the pin and body look correct for a 56 single to me. The stepped section goes into the holder. So if the holder does not screw home without the pin the logical conclusion is that the thread is damaged. May well be recoverable with a tap (cannot help with the thread form). I would grease the tap to try to pick up the swarf reversing it out and cleaning and regreasing regularly and clean up throughly afterwards. Someone else may be able to help with the thread.
clive
if it ain't broke don't fix
Mick D
Posts: 2886
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: G3 oil pump guide pin screw/body

Post by Mick D »

Hi

The thread in the photo is 3/8" x 24 TPI which is a standard UNF thread and I'm pretty sure that's correct for the engine.

I'd have a look up the hole in the crank case with the aid of a strong flashlight and mirror before I introduced a plug tap, there may be something obvious blocking the thread or the travel of the guide pin.

Regards Mick
tippi11
Member
Posts: 72
Joined: Sat Dec 01, 2018 9:59 pm
Location: Germany

Re: G3 oil pump guide pin screw/body

Post by tippi11 »

Hello,
I will follow your hints later today or tomorrow by trying to look up the hole with a flashlight/mirror (tricky enough because the engine is still in the frame and proper positioning seems difficult). :ugeek:
Regards, Peter
Locked