mercury barrels con rod cut outs

Arthur...........I had a set of Atlas barrels that suffererd exactly the same problem. The local engineering works suggested two fixes which appear to work. First they roll peened the top lips to physically expand the sleeves and make a tigher interference fit. Then they drilled and pinned through the side of the sleeves and inserted brass pins to lock them to the original bores..

I have attached a couple of photos to show the amount of cut-away on both standard 99 and 650 barrels. The key point to remember when cutting these slots is to always leave the inside corners with round a rounded profile to prevent stress areas. The same as has to be done when under-sizing the crank shaft big end pins.

hello I do not advise fitting model 99 barrel on a 650  even that they do look the same but looks are very deceptive  as the 650 barrel are set back more to the model 99  and even with cut outs the engine will revolt of having them fitted  and may even break up,  inside if you have a set of 650 barrel that have not been re-sleeved correctly  then  get them re-sleeved  so they are correct  but this may depend   where you are in the country to get a good engineering service   , Yours  Anna J Dixon 

Hi Arthur - I have used a 99 barrel on a Mercury successfully for many years.  Get the slots machined in as per Phil's images and the spigots will need to be removed if they are still present.  If you use the early dynamo barrel it does look incorrect because of the hole for the clamp at the fore but it will still perform satisfactorily.  The finning on the 99 barrel is positioned slightly differently at the front because the exhaust port angles are less-steep but I ground away the offending edges (on the two top fins) to match with the head angle.  The cam followers should be replaced with the flat ones (for the cam) but again I have run the radiused followers happily with SS cam at steady riding conditions.  Not as quickly obviously but more economically.  If you do change the followers it would be better to use new ones.  If your Mercury ones are OK and you can be sure on which cam they sat, then you could transpose them into your 99 turrets keeping the same cam position. Cheers and good luck , Howard      

I was looking on the Norvil website a few days ago, they were listing a batch of new 650 barrels.  The site said they were for Model 99 as well.  Paul

Anna is quite correct in that despite having the same casting number (22709) the early 650 barrel was a little  different from that of the 99 model. Though the 99SS barrel was actually a proper 650 barrel without the cutaway sections. Causing confusing to some engine builders.

John Hudson said that at Bracebridge they had lots of problems with the 99 barrels when they first used them on the 650 engine. He mentioned that the power of the original 650 was too much for both the barrel and pistons and that both suffered from distortion and breaking up. So apparently the 650 barrel was beefed up somewhere/somehow.

Like Howard, I have used 99 barrels machined to fit a 650 engine and not really had any problems. The point that many people forget when converting a 99 barrel is that the piston of the 650 travels over a greater bore distance. Consequently, a used 99 barrel cylinder will need a rebore or honing to prevent issues with ridging caused by ring wear.