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Classic, Vintage & Veteran For Coventry and Meriden Models. Anything pre-Hinckley goes.

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Old 06-08-2006, 07:42 PM   #1 (permalink)
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I evaluating using a ten bolt head with a 750 big bore cylinder on my 1971-ish engine, currently 650/single carb. Will a ten bolt head work on a nine bolt cyclinder if I drill and tap the cyclinder for the extra bolt (or plug the extra hole in the head)? Or is the single middle bolt on a nine bolt head in a different position than either of the two middle bolts on the ten bolt head? Can nine bolt rocker boxes be used on ten bolt heads and vice versa? Or do I just need to hold out for one of the very late 650 heads that had the boss for the 10th bolt?
Thanks to all,
Patrick Cherry
Ventura, CA
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Old 06-08-2006, 08:34 PM   #2 (permalink)
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do it the easy way

get complete top end (Barrels up ) from a 750 and bolt it on


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Old 06-09-2006, 09:24 AM   #3 (permalink)
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I always wondered if you could just leave the 10th bolt out of the assembly? They worked for lots of years with only 9.

Same wonderment as to whether you could just slap a 9-bolt head on a 10 bolt set of jugs?

Anyone tried it? Success? Failure?
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Old 06-09-2006, 06:28 PM   #4 (permalink)
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Kadutz,
If you mean a 750 big bore kit, I already have the cylinder and pistons; I just need to decide what head to use.

If you mean use a later Triumph 750 top end, the cylinder will not work on a long rod engine unless I change the connecting rods -- which I don't want to do.

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Old 06-09-2006, 09:11 PM   #5 (permalink)
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If you have a 9 bolt 750 kit use the 650 head. Thats they way it was done in 70 when they did the conversions.

Question what do you expect to gain by going thru all the work of using a 10 bolt 750 head?

Years ago I saw a 58 or 59 preunit 650 with a 73 750 top end done on it. So I know it can be done maybe with more work than the owner would confess to

I think you should double check the front center bolt location
on the head. I think the hole location between the 9 and 10 bolt head is off by a small amount.
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Old 06-11-2006, 12:12 AM   #6 (permalink)
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Kadutz,

I am looking for whatever cylinder head works best (in terms of responsiveness to tuning) with a 3.090 (75.7mm) bore cylinder. A 650 head works with the 750 kits but it is not optimal. The last 9-bolt 650 heads, the ones with the bolt-on intake manifolds and the boss for the tenth bolt, have better port profiles and flow better than the earlier heads, as do T140 10 bolt heads. I also like the rocker box arrangement on T140 heads better. However, I'm not interested in re-engineering the top end just to make a 10 bolt head work.

I was hoping someone either (1) has seen it done and knows the answer or (2) has both a 9 bolt and a 10 bolt head on the shelf and could bolt them up with the cylinder faces together and compare the center bolt holes for me.

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Patrick Cherry
Ventura, CA
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Old 06-11-2006, 12:42 AM   #7 (permalink)
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cheap way to check is to lay a 650 & 750 head gasket on top of each other
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Old 06-11-2006, 04:31 AM   #8 (permalink)
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K, your so cruel. But right.
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Old 06-11-2006, 08:51 AM   #9 (permalink)
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I don't know about that head gasket check, as the SLIGHT difference (if one exists) in the alignment of the #9 hole, might be within the oversize of the gasket hole...
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Old 06-11-2006, 11:59 AM   #10 (permalink)
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Quote:
On 2006-06-11 06:51, GrandPaulZ wrote:
I don't know about that head gasket check, as the SLIGHT difference (if one exists) in the alignment of the #9 hole, might be within the oversize of the gasket hole...
Exactly. I have the tools to measure it, if that would tell me what I need to know. As anyone who has read the saga of the P39 (?) frame project knows, there is an enormous difference between drawing board theory and shop floor practice. I know how to make an early 650 head work with a Routt 750 barrel because I've done it. I know how to set up Mikuni carbs for that combo because I've done it. I know how to put a late 5-speed trans into 4-speed cases because I've done it. I don't know what it takes to make a 10 bolt head work on a 9 bolt cylinder because I haven't done it. I am not specifically looking to use this combo, but since I am going to have to buy the head and rocker boxes anyway, I would rather get whatever is best and just do it once.
Thanks,
Patrick Cherry
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