Cyl heads for 1098

Side valve, 803, 948, 1098., 1275 and Vizard mods

Re: Cyl heads for 1098

Postby bmcecosse » Wed Aug 20, 2014 10:28 pm

Yes and yes - but the improvement in economy will be marginal.... And don't pay more than £10 for a cam4810 head! ;)
 









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Re: Cyl heads for 1098

Postby joshhicky » Mon Oct 20, 2014 7:50 am

Hi Everyone, Just a quick question when an exaust valve is fully open what clearence should there be between the bottom of the valve and the block. (how much more travel should the valve have)

josh
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Re: Cyl heads for 1098

Postby bmcecosse » Tue Oct 21, 2014 8:25 am

I suggest 40 thou PLUS the gasket thickness. I think some take a chance on less... In theory just the gasket thickness should be enough, but with valve float at high revs.......
 









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Re: Cyl heads for 1098

Postby joshhicky » Tue Oct 21, 2014 8:50 am

I was thinking along them lines, i have 75 thou so am happy with that, i was just checking what others thought. thanks josh
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Re: Cyl heads for 1098

Postby bmcecosse » Tue Oct 21, 2014 10:40 am

It only matters if you have fitted larger exhaust valves to a 'small bore' head - or have fitted a 940 head. Otherwise, the exhaust valves go down the bores, so there is no chance of a collision...
 









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Re: Cyl heads for 1098

Postby graeme_fryer » Tue Mar 03, 2015 10:35 am

Hi guys,

I've just got hold of an A+ 12G940 head with a view to fitting it to an otherwise standard 1098. I've measured the valve to deck height and have only 6.8mm so I intend to "sink the valves" to get the 8mm clearance recommended. If I'm correct, the A+ should have hardened valve seat inserts, so ......

- Will the inserts take the valve seats being cut down 1.25mm (.050"), or would it be better to sink the seats to maintain material thickness?

- As the A+ head has no thermostat bypass tapping, can I use a metro style plate that fits under the thermostat housing and feed back into the heater return? What have you guys done?

- I'm based in Burton on Trent. Has anyone used a machine shop in the Birmingham, Derby, Nottingham, Coventry area they could recommend?

Many thanks,

Graeme
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Re: Cyl heads for 1098

Postby bmcecosse » Tue Mar 03, 2015 12:40 pm

I would try cutting down the seats slightly -and perhaps shave 20 thou off the valve faces... The alternative is to make a 50 thou 'pocket' in the block under the exhaust valves - but then there is no going back...... Use a metro water pump (or block the outlet on your 1098 pump) - open up the heater valve connection at the back of the head, and use it for the heater - which you leave open all the time. A single 3mm hole drilled in the thermostat rim allows enough water to circulate until the stat opens - and gives you MUCH better heater action! I assume you know to use 1275 rockers and a 1275 gasket - and to file the top of the water pump to ensure the head can sit down tight on the block.
 









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Re: Cyl heads for 1098

Postby graeme_fryer » Tue Mar 03, 2015 2:02 pm

Hi,

Thanks for the quick reply :D

I don't want to pocket the block and risk exposing the top ring, so I'll do all the necessary work only on the head. I could grind .020" off the face of each valve using the universal grinder - that's a good idea to limit the seat work, but I don't have a valve seat cutter so I'll still have to get that done by a 3rd party. Are the Valves case hardened or through hardened? (Don't want to face grind them and break through the "skin")

It had a new water pump recently so I'll just block that for now and I'll machine the necessary off the top to seat the head while I'm in the tool room.

The heater valve connection at the back of the head is already drilled through and 2 studs fitted! Just for clarification - why must the heater be open all the time? Is the single 3mm hole drilled in the thermostat rim not enough on it's own until the thermostat opens?

Yep, I'll be using sintered 1275 rockers and a 1275 gasket.

Thanks again for your comments.

Cheers,

Graeme
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Re: Cyl heads for 1098

Postby bmcecosse » Thu Mar 05, 2015 12:03 am

Leave it open to ensure adequate water flow round the back of the head. Also stops sludge building up in the heater matrix. I assume the valves are hard through. It's actually better to use a leaded head for this job - the valves have usually sunk themselves down enough to get away without any machining....
 









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Re: Cyl heads for 1098

Postby gyp » Sun Oct 09, 2016 10:18 am

Hi all,

So after reading this thread I have a bit of a dilemma, do i put the stg4 jan speed fully ported head on the 1098 block or a 12g940 that I have lurking? They will be used with either a 649 or 895 cam, they are surprisingly derivable if timed in well.

head spec on me janspeed is :inlet valve 31mm , exhaust valve 27mm with 0.032 skimmed and 25.7cc volume.

Any ideas which might be the better option??
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