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Qualcast Suffolk Punch 43S Engine Noise

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RickT Thu, 25/07/2019

I don't know the exact age of this machine but as label says Birmid Qualcast (H&GE) Ltd I assume it is 1980s. Part No is L23981, Serial No. 039643/I. Electronic ignition and delOrto carburettor. Engine No. G 581132. Can anyone confirm age?

However my real problem is that after a few minutes the engine starts to make a loud metallic 'clacking' sound and loses power and halts.

10 years later and I have now stripped the engine - decoked (it wasn't that bad), replaced head and other gaskets on carb. Also had the carb ultra sonically cleaned. I didn't go as far as removing the valves on this strip down but movement and seating seemed ok. After a few pulls it started and ran well and pulled very well when mowing a strip. Was then going to optimise idle speed/jet position but then the same 'clacking' noise and loss of power and stops. Could restart it once but soon the same problem.

The gap between tappet/lifters and valve rods seemed to be ok. I assumed some sort of valve problem when hot but not sure where to go next......

Any suggestions?

Thanks RickT

Forums

wristpin Thu, 25/07/2019

Interesting one!  Your engine will have an alloy crankcase with pressed in  hardened steel valve seat inserts. I'm guessing that when warmed up one of the seats is coming adrift. I've never never experienced it on a Suffolk/Qualcast but it was not uncommon on some Briggs and Stratton engines. Particularly if they had suffered overheating  due to poor maintenance -  debris choking the cylinder fins etc. 

RickT Sun, 28/07/2019

Thanks for your suggestion  - stripping down and removing the valves etc is my only option I think. It may reveal some seat issue.

I will post an update after I find the time to strip the engine down next week.

Many Thanks RickT

RickT Mon, 29/07/2019

I have now removed the valves and have found the inlet valve seat to be loose - ie I can rotate it a little (but wont come out using hand pressure only). When hot I can imagine it may move a lot more and at the very least disturb the inlet timing.

Anybody know of a fix for this? I have seen a video of someone using a punch around the circumference of the valve seat to increase the friction between block and valve seat which would have to be a last resort....!?

Many thanks RickT

 

wristpin Mon, 29/07/2019

The video is more or less correct and is basically the method recommended by Briggs and Stratton

https://www.dropbox.com/s/7c5htn653sn4jm3/Briggs%20loose%20valve%20seat…

Points to note

Careful positioning of the three equally spaced centre punch impressions just far enough back from the intersection of the seat to the block so as to squeeze the block material against the seat and centre it up.

Then doing the peening one at a time from each centre pop so that the pressure is applied evenly around the seat..

In an ideal world you will then re-cut the seat so as to ensure concentricity with the valve guide and hence the seat.  If you don't have access to a valve seat cutter  you may have a problem in getting the "perfect" lapped track between valve and seat but I suspect that plenty of reasonably successful jobs have been done without!

hillsider Mon, 29/07/2019

I have successfully used this method of securing a loose valve seat on a Briggs and Stratton engine but not knowing any differrent I used six equally spaced centre pops. 

 

RickT Mon, 29/07/2019

Thanks wristpin and hillsider

Good to have confirmed that this is not only the last resort - but the only resort!

Many Thanks

RickT

wristpin Tue, 30/07/2019

A bit more detail on valve seat repair taken from a book Small Engine Secrets and Solutions written by John Carrow who, for many years was Briggs and Stratton's service manager in Australasia and the South Pacific.  The book is now out of print but if one can be found on Amazon or an auction site it is full of good practical advice from a man who has "been there and done it."

ISBN 0-9585317-0-6

https://www.dropbox.com/s/tdun7bqj1lcbxqd/Briggs%20valve%20seat%20repai…

Chris G Tue, 30/07/2019

Bit of a tease, sounds like a good resource, can't find one anywhere outside of Aus  - keep looking I guess

RickT Wed, 31/07/2019

Thanks to everyone especially wristpin for the valuable data to complement the experience,

Inlet valve seat successfully punched and peened in place as per B&S guide! Re-lapped valve and seats (on both valves).

Following rebuild motor starts first time every time and no recurrence of the noise during two ten minute runs.

A good sign is that setting idle mixture and speed was as straightforward as it should be....

Many thanks again.