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Collection, Preservation and Display of Old Lawn Mowers

Qualcast Suff. Punch 35S

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I have a Qualcast Suffolk Punch 14" (model 35S L 80162)  which belonged to my father from new. It is fitted (unfortunately!) with the notoriously problematic Dellorto FHC 2013A carburettor. This I think is the main reason the engine has displayed all the usual symptoms of only wanting to run when fully/partially choked. All parts of the fuel system including tank,  carburettor & all jet orifices have been thoroughly cleaned with little dirt found. To eliminate other possible problems, I have removed the cylinder head, carefully cleaned same together with the block and ground in the valves.

Now we come to the reason for this post which has caused me somewhat of a conundrum! On checking respective valve/tappet clearances, I find that the gaps I had previously obtained from your General Forum (courtesy of Member wristpin), namely Inlet 6 and exhaust 11 thou are reversed on my machine. I have the original "Operating Instructions" manual which shows that the tappets share the same part no. whereas the 2 valves have different part nos. Also the valve fitted on the exhaust port side of my engine has a small 6mm dish in the centre which I believe is to produce "swirl" to aid combustion. The head has never previously been removed from the engine and during dismantling & reassembly the valves were labelled & kept separate. Valve clearance is non-adjustable, so to create different clearances either the 2 cam lobes have different profiles OR inlet & exhaust valves are of different lengths. First question: Can someone help clarify this for me? Second question: Are the respective clearances I've obtained from your most useful General Forum correct or should they be the other way round? (Certainly, I believe it is normal for the exhaust valve to have the greater clearance to allow for expansion as a consequence of it getting it hotter).

If the clearance data IS correct, then it means the valves have been juxtaposed and, as far as I can see, this must have been at time of manufacture but I find it unlikely this would have happened. So any help that Members can provide (and maybe especially from wristpin who seems to have considerable knowledge of this engine) would be greatly appreciated.

A final observation is that on peering into the back recesses beyond the valve springs, it is apparent that the aluminium external cylinder casing is "crazed" with a criss-cross pattern of hairline cracks  -  fortunately no such damage is apparent in the actual cylinder bore.

Even when this mystery is solved and the head replaced with new gasket, I suspect the poor running will persist due to the carburettor the poor engine has been lumbered with. As it seems that the alternative adjustable main jet that at one time could be obtained from Qualcast is no longer available, does any member have any experience of delicately trying to modify the main jet?

Mike  

Forums

wristpin Wed, 03/08/2016

If you have the A114 six thou on the inlet and ten on the exhaust is correct.

it is quite normal for the inlet and exhaust valves to be of different configurations and made of different materials as the inlet is cooled by the incoming fuel / air charge while the exhaust is constantly blasted by the outgoing hot exhaust gasses. In your case the flat inlet and semi tulip exhaust is normal.

I would open the exhaust up to the recommended ten thou but I wouldn't worry too much about the inlet being four thou too wide. It may have been set too wide from new or there may be some premature cam, tappet or valve stem wear. At the point of manufacture the engines were probably selectively  assembled  using the " nearest fit" valve from the rack and may be the man or robot was having a bad day. 

The marks at the back of the valve chest are probably nothing to worry about; just surface imperfections in a mass produced casting.

I wouldn't give up on the carburettor until it's been ultrasonically cleaned. There are hidden  small passages and drillings that are inaccessible to aerosol cleaner and bits of wire etc. One area that is sometimes overlooked is the well in the bowl nut. Crud can collect in the well and get sucked up into the emulsion tube. Then when the engine stops, fall back into the well.

 

 

 

 

Tinker Wed, 03/08/2016

Thank you wristpin for your response. I'm actually not sure which engine I have  -  the serial no. is 987060X and maybe the first two nos. indicate that it is actually the A98. It is also marked 0.95kw  3000. What do you think? If it is the A98, does this have different clearances?

In my ignorance, how would I increase the clearance of the exhaust valve as I thought there was no means of adjustment? 

Thanks for the suggestion re the carburettor bowl nut but had spotted this tip in earlier posts and it is clean.