[Thomas]

that's the problem I'm already at +030" I'd have to get the Bore re-lined and I've no idea who could do that

Sorry, I missed that. Just some weeks ago I have my BSA barrel be re-lined in a regular engine workshop. I would hence say that this shouldn't be too big a problem. I am not in England but see that again Cox and Turner does that. But again, must be workshops all over the country.

[Russ]

Hi Russ!

That piston is a bargain and would already be mine if I would need a standard size. Ask Cox and Turner. They can certainly deliver the rings and the circlips should be available in any regular tool shop. The Thorntons information seems to be somewhat irritating (to be modest) because it would mean that you can not use at all any piston without circlips. Just two months ago I bought matching wrist pin circlips for a BSA NOS Hepolite and they sit well. Note that this piston is presently the only available one. There are none in the club shop.

that's the problem I'm already at +030" I'd have to get the Bore re-lined and I've no idea who could do that
Cheers, Thomas

[Thomas]

Hi Russ!

That piston is a bargain and would already be mine if I would need a standard size. Ask Cox and Turner. They can certainly deliver the rings and the circlips should be available in any regular tool shop. The Thorntons information seems to be somewhat irritating (to be modest) because it would mean that you can not use at all any piston without circlips. Just two months ago I bought matching wrist pin circlips for a BSA NOS Hepolite and they sit well. Note that this piston is presently the only available one. There are none in the club shop.

Cheers, Thomas

[Russ]

that piston has no rings and more of an issue is it doesn't have any wrist pin circlips......speaking to Thortons and the chap I spoke to siad buying a piston without its wrist pin circlips is a chancey thing trying to get the exact circlips to fit perfectly would be pretty impossible apparently......I'm not sure it's worth the aggro.....any opinions

[Russ]

I'm on it thanks for that......wouldn't sleeving the barrel be a major job though wouldn't it as the bore is the barrel...

[wessex_man]

Here you are Russ a NOS piston It's a standard size. So you would have to sleeve and rebore might help give you options BIN though so don't know how long it will last. 26/03/23
eBay item number:115744778984

[singleminded]

Some of the inlet guides for use with Tulip guides had the lower end of the guide tapered to accept the tapered valve stem to avoid the valve jamming.
I had to open one out for one of our members as the valve was sticking.

[Thomas]

No rush, Paul, I just got newly made guides from my workshop and I am happy if I can later get a new set at all. And only then I need the measurement information. Many thanks for your efforts which I appreciate!
Cheers, Thomas

[phutton]

Sorry Thomas, I don't know exactly, but I suspect it is the region of 3.5mm. I will need to do a check to compare the tulip valve with the standard one. I won't be able to do this until I have sorted out the NOS guides sometime in January.
P.

[Thomas]

Very good, thanks a lot Paul. I will oder a pair as soon as they are available. Do you have an idea about how much one needs to shorten the guides for Tulip valves?

[phutton]

No Thomas, the guides are made from nodular iron, such as Meehanite, and are very easy to machine. This will not be necessary with the standard valves that we will be stocking.
P.

[Russ]

...Also valve guides will be available about the same time. These are NOS Sunbeam, but need sorting as we have acquired a large random batch.

We no longer supply tulip valves as these require a taper in the guide, or the guide needs to be shortened. The performance gain is marginal, and the shape was used to reduce weight and make the head-stem connection stronger. Not necessary with modern valve materials.

P.

good oh.....I just asked about guides and springs over on my other thread....I have my answer on the guides what about the springs and pistons......answer over on my other thread Paul....https://www.marston-sunbeam.org/sunbeamForum/index.php?topic=1112.0

[Thomas]

Hi Paul!

We no longer supply tulip valves as these require a taper in the guide, or the guide needs to be shortened.

That is an important information I didn't know. The spare branch should explain that when selling. I mean, the material will be hardened and needs respective tools to shorten the guide. No straight forward procedure for most of us.
Cheers, Thomas

[phutton]

...Also valve guides will be available about the same time. These are NOS Sunbeam, but need sorting as we have acquired a large random batch.

We no longer supply tulip valves as these require a taper in the guide, or the guide needs to be shortened. The performance gain is marginal, and the shape was used to reduce weight and make the head-stem connection stronger. Not necessary with modern valve materials.

P.

[Thomas]

would you know if they're made from SG Iron

I don't know but I hope so...

[Russ]

Hi Russ, I got nitrited tulip valves from GS Valves. They make them according to your needs but already have a large number of drawings for Sunbeams. Guides are already on the way to the club shop. Drawings can also be found there. In the Beaming spring issue there will be an article where I describe some details about them including information from Chris Odling about how to heat tread the cast iron.

Cheers, Thomas

Valve guides on their way to the shop......I'll be looking out for them.....would you know if they're made from SG Iron

[Thomas]

Hi Russ, I got nitrited tulip valves from GS Valves. They make them according to your needs but already have a large number of drawings for Sunbeams. Guides are already on the way to the club shop. Drawings can also be found there. In the Beaming spring issue there will be an article where I describe some details about them including information from Chris Odling about how to heat tread the cast iron.

Cheers, Thomas

[Russ]

I totally agree with you Thomas that pistons are now high on our priority list.
Vic

Hi Vic can you add to that valves and guides as well....I've just come back from having my head assessed (not my head you understand as that's been worn and empty for a good few years...LOL) and my valves are worn as are the guides and seats

[VicYouel]

I totally agree with you Thomas that pistons are now high on our priority list.
Vic

[Thomas]

Very good! But in the long-term even this does not help, especially for those who have not stored a piston (like me).

[wessex_man]

Thomas thats why the one I bought is still in it's box.

[Thomas]

The 7.5 piston is slightly heavier. What about the balance to the crank? The 7.5 JP piston seems to be out then.

In general, I wonder if this issue is in the focus of the club spares shop. I mean, a t a certain point we all need new piston (standard or oversize) but there is indeed almost nothing available.

[wessex_man]

Chances of getting a new old stock piston is remote I got my last one 5 or so years ago.No Sunbeamland ones availble now. There's a JP on ebay at the momment which is currently the main option availible. Basically yes pistons will change over. They are heavy in comparison. I'd probably fit a compression plate between the barrel and crankcases though if you go down this route.

[Russ]

I'd be happy with the standard piston on the right in the first picture.....I guess the question is it possible to swap out the 6.5:1 piston for the 7.5:1 piston without having to alter the deck height.....is it just a straight swap?

[wessex_man]

Interesting post. 80mm pistons are a bit thin on the ground especially Beam ones.
Here's some pictures of a high compression and std piston.


The piston weight of each are the same, pretty much (within a few grams allowing for the two rings I have on one and not the other).

Here's a JP piston by comparrison middle one.

 

 
 

[Russ]

The 7.5 CR piston (Hepolite 3291): Compression Ht = 1 27/32", Piston length = 3 15/32"
The 6.5 CR piston (Hepolite 3658 1926-1930): Compression Ht = 1 15/32", Piston length = 3 3/32"

All other significant dimensions are the same, but the 3658 has two rings at 2mm (0.0787") thickness and the 3291 has three at 3/32" (0.0938"), the third being a scraper ring.

P.

CR height....that's measured from the Center line of the wrist pin to the crown isn't it.....so 3/8" difference in crown height between the two pistons that's quite a big difference........I'm starting to wonder if the valves for the M90 were the same length as the M9 then perhaps the M90 cams were of shorter lift but longer duration allowing the 3/8" CR height difference I'll have to speak to Thortons to see what they know.... blimey sorting a piston is a whole can of worms isn't it......By the way Paul I got the new Handlebars and clutch parts very nice thanks.....I've also just received back my re-corked clutch I've also bought some new 3/16" Shimano bearings so clutch will be back together shortly once I've sorted measuring and fitting the new pushrod.....my oiling system should be all back together as it would have been when it left the factory Hand pump and drip feed sight glass feed pipes all renewed just off to bend some 5/16" pipe 

[phutton]

The 7.5 CR piston (Hepolite 3291): Compression Ht = 1 27/32", Piston length = 3 15/32"
The 6.5 CR piston (Hepolite 3658 1926-1930): Compression Ht = 1 15/32", Piston length = 3 3/32"

All other significant dimensions are the same, but the 3658 has two rings at 2mm (0.0787") thickness and the 3291 has three at 3/32" (0.0938"), the third being a scraper ring.

P.

[Russ]

According to the Hepolite data, the main differences across the years for M9/90 pistons has been the ring configurations. Across the models, the variations are the compression height and hence the length of the pistons. Each of the piston configurations will work in each of the models/years. You may have to back off the ignition advance slightly for the 7.5 piston, but that should be all. Thorntons would be able to advise on piston clearance.
P.

Thanks Paul......I didn't think there would be much difference in engine configuration between the M9 & M90 why go to all the expense of altering the basic engine specification I guess the main differences would be a different head (2 port) different cams different Carburettor different valve/ ignition timing......just guessing here but maybe the difference between the 6.5:1 and the 7.5:1 pistons if all other dimensions of the pistons are the same must be the crown height meaning the Valve cutouts will be deeper and possibly the ring configuration........do we know the dimensions of a standard 6.5:1 model 9 piston

[phutton]

According to the Hepolite data, the main differences across the years for M9/90 pistons has been the ring configurations. Across the models, the variations are the compression height and hence the length of the pistons. Each of the piston configurations will work in each of the models/years. You may have to back off the ignition advance slightly for the 7.5 piston, but that should be all. Thorntons would be able to advise on piston clearance.
P.

[Russ]

I've had a rough measure of my bore....only at the top part mind....with a set of digital Verniers and it measures 80.24mm give or take so at least I know it's an 80mm piston of some description so if I went +040" I'd probably be ok but I think I'll go +060" to make sure......anyone know what the piston to bore clearance should be for +040" piston and a +060" piston and ring gaps

[Thomas]

Hi Russ, if you can not wait for the correct piston and if you are willing to modify the motor (I don't know what a 1927 says about a 1931 compression) you can calculate the CR plate thickness by the ratio of the two CRs. A 7.5 CR is about 15% higher than 6.5. Hence, you need to increase the combustion chamber volume by 15% to reduce it to 6.5. Because the bore remains the same you need a plate thickness of 15% of the piston stroke. I believe the latter is 98mm. Hence, you need a plate of 0.15 times 98mm which is 14.7mm (does the cylinder than still fit under the frame?). That are theoretical considerations which do not include any potential additional effects in the chamber. But I believe, the old engineers didn't consider gas turbulences and other sophisticated influence on the motor power. 
Cheers, Thomas

[Russ]

Thorntons in Shrewsbury have two +.060 M9 pistons in stock see: https://www.fwthornton.co.uk/motorcycle-pistons.

p.

7.5:1 CR for 1931 model 90 would this be suitable for a 1927 model 9 would I have to put a CR plte under the barrel to reduce the CR if so how thick would it need to be.....having said that wouldn't running a 7.5:1 CR instead of 6.5:1 CR be ok what harm would it do isn't the model 90 the same as the model 9 with the exception of a twin port head and the oiling system....are the crank journal bearings different.....I've read that some owners with twin port heads actually blank one port off as it supposedly increased performance

[Thomas]

I believe Pistons are an issue for the club spares. I mean, almost everybody needs a new piston now and then but they are not available. Even at Sunbeamland they are all gone.
Cheers, Thomas

[phutton]

Thorntons in Shrewsbury have two +.060 M9 pistons in stock see: https://www.fwthornton.co.uk/motorcycle-pistons.

p.

[Russ]

I hav now discovered the makers name on the piston in my bike "COVMO" Coventry Motors I believe and I'm now more than ever convinced it's a Norton 16H piston as this one for sale is on ebay and it's a +030"...https://www.ebay.co.uk/itm/325358407988?hash=item4bc0df5134:g:bK0AAOSwO6diuC40
and here's some pictures of manufacturers ads you never know someone might be interested.....LOl

[Thomas]

Pistons are a problem that we do need to get to grips with.

Yes, Paul, I would appreciate any initiative. I still use my original piston but I certainly need an oversize one within a reasonable time. And the Oversize +20 thou is out of stock... 

[Russ]

I don't think it would be a Sunbeam SV piston - they are 70mm, 77mm, or 85mm. Pistons are a problem that we do need to get to grips with. We have plans but need to make some decisions on specs and the finance required.

P.

correct P. I'm sure it's not which is why I said from a SV engine knowing Sunbeam SV's only being 77mm but it could be a Norton 16H piston (79mm) or Big 4 piston (82mm).....I need to find out if it's a Norton Big 4 piston as that'll mean my barrel has been over bored to 82mm +030" less any clearances so there wont be much point in me getting a Sunbeam model 9 piston 80mm +040" or +060"......I'll have a measure of the bore to see what I've got....just doing a quick calculation though using a 79mm +030" Norton 16H SV piston would give a size of 79.762" leaving 0.238mm piston to bore clearance so perhaps my barrel hasn't been overbored but just lightly honed......there again I'm probably talking total B*******.......LOL......still having said all that I can't wait for my handlebars to turn up.....yay

[phutton]

I don't think it would be a Sunbeam SV piston - they are 70mm, 77mm, or 85mm. Pistons are a problem that we do need to get to grips with. We have plans but need to make some decisions on specs and the finance required.

P.

[Russ]

yes I know but is the piston in my bike 6.5:1.......I have a sneaking suspicion my piston maybe 6:1 +030" from a SV engine as they don't have Valve cut outs obviously.....anyone know where I can get a new +040 piston (with Valve cut outs....loL)

[Thomas]

...is my piston actually 6.5:1 and not something less...

This page says you have 6.5:1.
https://www.motorcyclespecs.co.za/model/Sunbeam/sunbeam_model_9.htm

[Russ]

Hi Russ,

indeed, piston and bore look pretty good. No need to work on it. I am surprised, though, that the piston has no carbon layer on its top as if the motor is new. The head is also fine even if somewhat sooty. Note that the exhaust valve and guide are lubricated by the exhaust gases. The piston looks like my Specialoid. However, I have valve cutouts for my 6.5:1 machine. But it's ten years younger. If you can turn it over without any problem I see no reason to assume that cutouts are missing. I suggest to thoroughly lap the contact surfaces of cylinder and head. Look a bit suspicious.

Cheers, Thomas

thanks Thomas I would lap the cylinder head and barrel together as a matter of course with some fine chemo griding paste it's an easy task on the sunbeam without head studs in the way.....I have to remove the studs to lap the Nortons head and barrel together

Looks like someone has used a cylinder head gasket at some time. Marstons NEVER fitted one! The 6.5 CR pistons should indeed have a pair of small cut-aways in the crown, which might account for the fitting of a gasket.

P.

Hi Paul.....although my piston doesn't have the small cut away I'm positive the piston doesn't hit either valve...I kicked it over several times by foot and hand having said that the piston does come alsmost to the top edge of the bore but there but if they had hit there would be some tell tale signs on the piston and valve edges for sure and a there aren't any.....when I put it back together I'll get my boroscope down the plug hole to see what's happening....there are questions now...like ....did the original Sunbeam 6.5:1 pistons need the cut outs in the first place they are pretty small....is my piston actually 6.5:1 and not something less which might account for why I can turn it over fairly easily by hand does anyone know what pressure a model 9 with a 6.5:1 piston should hold as I could pressure test it easily enough.....are my cams the correct ones giving the right amount of lift are my valves of the correct length giving enough opening.....I've no idea......questions questions questions

[phutton]

Looks like someone has used a cylinder head gasket at some time. Marstons NEVER fitted one! The 6.5 CR pistons should indeed have a pair of small cut-aways in the crown, which might account for the fitting of a gasket.

P.

[Thomas]

Hi Russ,

indeed, piston and bore look pretty good. No need to work on it. I am surprised, though, that the piston has no carbon layer on its top as if the motor is new. The head is also fine even if somewhat sooty. Note that the exhaust valve and guide are lubricated by the exhaust gases. The piston looks like my Specialoid. However, I have valve cutouts for my 6.5:1 machine. But it's ten years younger. If you can turn it over without any problem I see no reason to assume that cutouts are missing. I suggest to thoroughly lap the contact surfaces of cylinder and head. Look a bit suspicious.

Cheers, Thomas

[Russ]

more questions just trying to establish what I've actually got......took the head off yesterday and I have to say I was pleasantly surprised at what I saw......the crown of the piston was clean and the bore looked in ok shape you can still see the crosshatched honing marks the inside of the cylinder head looks ok but was quite sooty......I'm going to fill the bore with some light oil to see if it stays put or drains away and I'll do the same with the cylinder head to see if the valves are letting by the reason is although this all looks good I could actually crank the engine over quite easily by hand but having said that it is only 6:1 CPR my old Norton is running at 9:1 and that's difficult kicking over with all my weight....does the piston look original I know it's not original as it's +0.030" what I mean is should it have some smallish Valve cutouts or is the plain top correct there's also some other stamping on the top of the piston.....COV*** and WM I would of thought some sort of makers mark any of you piston experts out there know who though