hi, i am just about to get a set of goldstar timing gears with cams off ebay
the cams are 65-2438 , 65-2436 . is it just the cams i need to fit to my m20
or the other gears as well , also do i use the standard m20 tappet settings

thanks in advance

Hi Dirk...You will derive little, if any, benefit from fitting Gold Star cams to a standard M20 engine...

Cams do not work in isolation from the rest of the engine specifications but in conjunction with them to produce more power...

The M20s performance is also limited by compression ratio, port size and shaping, combustion chamber shape and crankshaft weight (which limits revs).

These features would also require some attention for the Gold Star cams to function as intended...

You would derive more benefit in performance by enlarging your M20 to an M21 than you will from fitting Goldie cams to a standard M20...

The main limiting factor is the flywheel weight and consequent low engine revs along with relatively low gas velocities in the inlet port which ensure the larger valve overlap of the Goldie cams will not function as intended...Ian

In answer to your original question you can fit just the cams to the M20 engine...

I think those are pre war cam numbers that do equate, more or less, to later cams...I would have to check for their original application though...

You would also need to fit some inner valve springs...C15 inners are a suitable spring...

You can retain original tappet clearances but I don't run those myself, using a 'loose' .008" on the exhaust side and a 'snug' .008" on the inlet....Ian

I don't know the difference between Goldstar cams and M20 cams, but a trick with the Norton OHV 500cc ES2/Model 18 is to use 16H inlet cam as it has a longer duration and lift, and the 16H piston for higher compression as it's domed (you need to cut for valve clearance). Just because the OHV engine is faster they don't work the same as a side valve engine and if you put the ES2 cams in a 16H it would be slower..!

email (option): horror@blueyonder.co.uk

I've just checked those numbers and they are for a 1950 ZB Gold Star...

As such you can fit them into the M20 without any of the other GS timing gear...However, my original comments about the benefits (or not) still apply...Ian

They are mild cams, so wouldn't hurt. Just fill up your head with mig weld for more performance.this is my forth attemptto post. Driving me crazy!!!

thanks for the advice , guys . i will have a bit more of a think then, before i do anything.
reguarding welding the head , i have done a little cast welding but it involved preheating and using rods.
with you saying mig weld i asume you mean with suitable cast welding wire

I have access to a mig plant but only mild and stainless wire, any more advice is welcome. is there a shape to aim for with the welding and would it need blending into the face or would it be ok to leave below face level, if that makes sence . thanks

Dirk,

I have those cams in my 720cc engine along with a lot of other work. Email me if you want more information.

Jeff

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email (option): jjbandoo@aol.com

Very very nice Jeff. I'll be interested in how fast your nerves will allow you to ride it. Ron

email (option): ronpier@talk21.com

I'm embarrassed to say that the piston nipped up in the first few test miles. I've had the bore honed and it cleaned up with .004" clearance, so my spare piston will go right in. The squish was a bit tight with the piston just striking the timing plug which protruded less than .005 into the chamber, so I fitted a .005" thicker head gasket. I got the 10TT9 to accept an idle set screw using a straight spoke threaded into the cap, stopping the slide from above.

It should be on the road within the week. I won't be riding it with any confidence!

Jeff

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email (option): jjbandoo@aol.com

Hi jeff...How much 'pop up' did you use in the end?...Ian

Ian.

Pop-up is .186". A completely arbitrary figure chosen by looking at photos of Harley WR and KR cylinders. Squish was .024". See how the timing plug dug into the clay. Now corrected.


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Jeff

email (option): jjbandoo@aol.com

Hi Jeff...That's a tight(ish) squish...Watch out for piston/head contact when it's revving...

I'd be interested to know whether or not you experience any problems with that...Ian

Never understood the use of popup pistons. because you have to shave something off the head for clearance which defeats the purpose?

Pop-up allows a bigger intake throat between the valves and the cylinder to aid filling without lowering the compression ratio. My CR measured out to be 7:1.

It's one of the successful developments from so many years of running H-D 750 SV engines in Class C competition in the USA. They stayed competitive with 500cc BSA's and Triumphs until the mid-sixties. A good example of the triumph of development over design.

email (option): jjbandoo@aol.com

I saw Cal Rayborn racing a factory KR in the Transatlantic Trophy Races in the early 70s and it was an impressive machine even then...

A great time for variety in racing bikes with British, American, Japanese and Italian manufacturers all represented...Ian

Excuse my ignorance on M20's, is 4 thou the correct clearance for a 500cc piston? I'm in the middle of resleeving and boring a barrel and all the info I can find for a Norton says 5 thou - 10 thou for racing. Seems to be the same clearance for side valve and OHV engines. The place putting in the barrel liner, race speedway bikes, so similar engines. He said they run them at 8 thou clearance, maybe this is why your engine nipped up?

email (option): horror@blueyonder.co.uk

Well, .0035 was clearly not enough clearance. The piston that seized in my engine is a 90mm NASCAR- spec one-off JE piston that Ian developed. And yes, I'm nervous about running the next one at .004.

Jeff

email (option): jjbandoo@aol.com

OUCH .0035 is definitely not enough, and I was talking a 79mm piston..! I would say you need more than 5 thou for a 90mm piston to allow for expansion.

email (option): horror@blueyonder.co.uk

Looking at the damage on your piston, another 1/2 thou to .004 isn't going to stop that. You are going to do exactly the same thing again

email (option): horror@blueyonder.co.uk

I also have one of Ian's Pistons in my M21. Ian apparently uses 3 to 3.5 thou clearance on these but I think he has a very strict running in regime! They are high silicone and the expansion rate is apparently very low compared to standard pistons.
I used 4 thou and was very careful for 1000 miles and had I no problems. (it was a very boring 1000 miles though!)

Cheers
Pete

email (option): petercomley@web.de

I can't argue with that then Pete, that's very tight though. 750 Commando pistons have 4 thou clearance and they're a lot smaller. It sounds like your running in period is an art, to slowly size the piston to the bore without it nipping up. An extra thou might help here, but I'm not going to argue with Ian's recommendations for his pistons

email (option): horror@blueyonder.co.uk

These pistons will run in without problems at .004" in either SV or OHV applications...

'Run in' is the key part of that statement though...

Any comparison between these forged, low silicone pistons and original cast pistons is invalid...Material specification has moved on a long way since then and expansion rates are completely different...

For engines that are likely to have a much shorter or less rigorous running in period I would recommend another .001"..so a skirt clearance of .005"...

However, even this is less than the top clearance figure for a standard and 5mm smaller B33 piston for example...

I have run them in from .0035" without problems myself..though I like to bore my own engines 'snug' and then run them in carefully, particularly in the first few hundred miles...

I have liased with Jeff over his problem and made my recommendations for clearances before rectification work commenced on his engine...

Also, in the interests of a balanced discussion on what clearances are suitable for these pistons, I have to say there was one other key factor which has not been mentioned as yet which, in my opinion, led to the failure of Jeffs engine at a .0035" clearance...

Currently I recommend a .004" clearance and a full running in procedure as a 'standard' clearance for these pistons but would vary that to suit some applications, such as competition use or if used in heavy load environments, such as a bike fitted with a sidecar......Ian

Horror...in answer to your query on the 79mm piston .0045"-.0055" skirt clearance should be plenty...

.008" as suggested by your rebore shop would be far too much unless you are planning to thrash the nuts off it from the moment you start it up....

I assume you are talking about a solid skirt piston?...For a split skirt piston the clearance would be far less...Ian

Thanks Ian, that confirms what I was thinking as I don't want to get a new liner and piston wrong

Yes, the 8 thou was what they use on there speedway engines that are thrashed from the start, I won't be thrathing this engine straight away
They weren't recommending I have that much gap but we were seeing if the liner in the barrel was at all "usable" past standard, but I don't thing 8 thou would get rid of the ridge and score. As liners can't be rebored it'll need replacing. No chance of finding a better barrel either as it's the early type Model 18, I haven't even seen any on ebay. Someone's selling NOS 16H liners on ebay that should do the job nicely and a new GPM piston

email (option): horror@blueyonder.co.uk

['As liners can't be rebored it'll need replacing']..


Are you sure about that?...What is the wall thickness of the liner?...Or is it a material issue?

Even thin liners, say 1.5-2mm wall thickness will rebore OK ...

If the liner can't be rebored does that mean you can only buy standard pistons for this model?

BSA used hardened liners in the period just before the war but even these can be rebored.....Ian

As Ian said, my piston seizure was not due to his clearance recommendations but rather my application of Cerakote Micro-Slick to the piston skirt without checking the resulting clearance. I must learn to leave well-enough alone, or at least listen to the advice of one's mentor!

The gold color on the crown and other combustion chamber surfaces is a thermal barrier, Cerakote Piston Coat.
I'll offer a review of these and the other ceramics I used when I get some miles on the bike.

Jeff


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email (option): jjbandoo@aol.com

Could the heat build-up in the piston from hitting the head be off any factor in the seizing?

Sorry to see such nice parts damaged so quickly, good luck!

Ah that's bad news Jeff, yes you'll loose a few thou clearance with that stuck on the piston, it seemed like a good idea at the time. I hope all goes well with the rebuild.

['As liners can't be rebored it'll need replacing']..


Are you sure about that?...What is the wall thickness of the liner?...Or is it a material issue?

Even thin liners, say 1.5-2mm wall thickness will rebore OK ...

If the liner can't be rebored does that mean you can only buy standard pistons for this model?

BSA used hardened liners in the period just before the war but even these can be rebored.....Ian [/quote]

Sorry to hijack this thread with my engine rebuild. The liner in the Model 18 barrel is about 2mm Ian, just measured the NOS 16H liner and that is a fraction over 2mm as well. We weren't sure if there was enough meat on it to go +20 as the last thing I want is it breaking up. Then after reading the manual it says liners can't be rebored, they need replacing again. It also looks like there was only +20 and +40 oversizes originally.

It says bore out to 3.250" to fit the liner which works out about right 79mm + 2mm + 2mm liner =83mm = 3.267". So somewhere near using a quick measure with the verniers.

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email (option): horror@blueyonder.co.uk

Hi Horror...It says liners 'Will not' be rebored...not 'Cannot be rebored'...It's an instruction...

What they mean is that when a replacement liner is fitted it must (will) be bored to 'plan' or 'standard' size, not an overbore size (.020" or .040")...This is to avoid wasting rebores

The instructions follow normal practice...A rebore to .020", then a rebore to .040" then a new liner and a rebore back to STD...

Exactly the same as an M20 in fact....

If you think about it, if a liner was fitted from new and you could not rebore the liner beyond STD there wouldn't be any oversize pistons available...Only STD pistons and liners....Ian

Ok.. seems an odd thing to write in the instructions and quite ambiguous, I would have thought it was obvious that a new liner would be standard bore.

The barrels don't come with a liner from new, so you would use a +20 then +40, as there was no +60 a replacement liner would have to be fitted or the barrels scrapped, this is a last resort to give them one more "life". So over sized pistons would still be needed. It also says that "All stages subsiquent to fist linering will consist of linering back to plan size". That would suggest that they can only be used once, then need changing..?

If that liner was bored out to +40 it would be 1mm thick, isn't that too thin..?

Thanks for pointing that out to me though Ian, that will make life easier if that is the case, although I'll have to change my new piston for a +20 I'll do a bit more research

email (option): horror@blueyonder.co.uk

Hi Horror..If you fit a liner you can bore it to any of the sizes quoted so far...An M20 liner can also take a .060" overbore but to be honest I can't remember how thick an M20 liner is!

With the liner dimensions you have stated you can go to .020" or .040" but particularly with the latter size you are obviously 'burning your boats' as far as any problems are concerned...In that event you'll be right back to fitting another liner...

If you are expecting to do high mileages on the bike I'd go for a standard piston so you have as much 'in hand' for the future as possible...

If it's going to take decades to cover say, 50,000 miles then a .020" could go in as a first bore size...Ian

I think bigger pistons have been made since those publications. I'm 95% sure I fitted a +60 from Russell's in my 16H. I'll let Ian work out what CC it is now Ron

email (option): ronpier@talk21.com

509cc.... ...Ian

A Hepolite Norton 500cc liner has an OD of 82mm.

That would make the liner thickness 1.5mm at standard bore, 1mm at +20 and 0.5mm at + 40
I'll bore it out to + 20 and see what it's like, one bore size should last me a life time so I'm not worried about wearing it out. Thanks for all the info

email (option): horror@blueyonder.co.uk

Ok, a bit more research on this and I realise I have my figures completely wrong here. Although 20 thou is 0.5mm, when bored it is a 10 thou cut so not 0.5mm off the thickness of the liner, but 0.5mm of the total thickness...! D'OH So the liner will easily bore out to this size

Thank you Ian, for pointing out that the liners can be bored

email (option): horror@blueyonder.co.uk