1929 500cc OHV Sloper Valve guide clearance

Started by BEVANC, 08 January, 2025, 22:16:21

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BEVANC

Hi folks, I've found a lot of postings on this forum about valves & guides, but can't find anything on clearances, so - what would be a safe valve guide clearance if using cast iron guides ?
Thansk,
Bevan

Dean Southall

Hi Bevan
I have summarised the servicing schedule in the document attached which includes valve clearances
cheers
Dean
BSA: turning ordinary men into mechanics since 1910

scifi

Hi, I have seen that Dean has sent you the valve tappet clearances.

You wanted the Valve Guide clearances, for cast iron guides.   
I would think these need to be 2-3 thou. maybe more for the exhaust valves.   They are not so easy to measure to any ultimate accuracy, but depends upon your method of drilling/reaming the guides.

BEVANC

Thanks for the feedback. That summary is useful thanks, but I was most interested in the valve to guide clearances.
My valves and seats seem in good order, but there is quite lot of play in the guides. An engineer I consulted was suggesting using an insert of some sort but that made me nervous. I think he was hoping to avoid driving out the guides since the head is quite vulnerable to cracking I guess. However, in an exposed valve low lubrication situation, I have been told that cast-iron guides are still the best.

scifi

Cast Iron Guides are available in the car market, maybe one of these can be turned down to the correct size and shape.   Most of them are in Metric sizes...  Are your valve stems metric or imperial..?  Also are you fitting new valves, as the old ones could be worn...?

The Guides need to be up to +1.5 thou bigger than the hole in the cylinder, to be a tight friction fit.   Removal and fitting is best done with an air hammer, and guide punch, which basically vibrates them into position.   Once fitted they will be tight in one spot, because of the friction fit.  This needs to be reamed to the correct tolerance ( about 3 thou inlet 4 thou exhaust.)

The internal measurement of the guide can be done with a Split-Ball Gauge and Micrometer.

Cast Iron Guides are quite good, well yours have lasted almost 100 years..!

Steve.S

I agree with scifi, although I would take 0.003" to 0.004" as being absolute minimum clearances.
Also, be sure that valve stem and guide bore are clean and oil free before checking clearance.
Cast iron is the only material to use for Sloper valve guides.


BEVANC

That info is a great help, thanks very much. The valves are presumably not original (I'm guessing the originals may have had BSA markings ?), but have very little wear so I think can be re-used but I'll get an expert opinion on that.

I don't have any engine history - the bike was directly exported from the factory to Eastern Europe where it spent 85 years of its life. Was geared lower than sidecar so I suspect it has down some fairly gruelling service. I am determined to get it back to good order and a gentle retirement puttering around here in N.Z.

I'm doing a precautionary total strip down - however the bike was running really well, despite very worn guides, a broken valve spring, badly worn exhaust rocker pad, worn cams, and two fractured rocker box mounts. Rather surprisingly, the main and big end bearings seem as new. Minimal play in the rocker spindles, which were very, very well greased - the exhaust rollers seem new; the lnlet rocker spindle has been bushed.

All good fun :)
Thanks again for your helpful advice.
Cheers,
Bevan