Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board Robs engine rebuild help thread

Hi Fellas,

I had a lot of problems with my Rickman Metisse last year so in November I sent the bottom end to SRM in wales and this turned up this week.

I got new oversized pistons and have now delivered the devimead barrel to my local engineer shop for a bore and hone.

I have built many 2 stroke engines before, but never a 4 stroke, so I have lots of questions comming and thought I would keep it all tidy in this thread.

I bought a Thunderbolt head from ebay and it was a real mess. I decided to swap out the Lightning head to thunderbolt because I belive that Rickman scramblers came with a T-bolt head from Rickman as standard and It should give me a little more torque.





The head has been welded, faced, fins and threads all repared. Ohh... Big valves and ported to lower the comp a little for modern (crap) fuel. All to help this baby start a little easier.









New spitfire cam, SRM Rods, sludge trap cleaned and dynamic balancing. Engine case repairs include gasket and bearing faces and of corse the singing and dancing end feed and needle bearing conversion. The side cases were blasted, dechromed and then polished. This motor was crinkel painted black when I sent it to SRM.













The cylinder should be back with me in about 10 days.

I will need some assistance on some proberbly pretty basic info, like push rod order, clutch rebuild and the odd niggle that might crop up.

I am hoping to take the bike to a local bike show in April.

At the moment we have 1.5 meters of snow and today it was -12c in my garage (-32 effective outside! ) so hope it warms up a little when I get the barrel back.

First job is fitting the gearbox and new bearings and seals which I wont recieve until next week anyway.

Nice to see.......even better to open.
What size final drive, my big bore runs a 21 tooth without any issues at all.
I was just about to advertise a set of those pistons as I had to go larger again.

Yeah, I`m running 21-47

Pistons are 79.5.

That's the size.
I had to go to 80, but I already had the 79.5 purchased, my mistake. I have two sets of jugs might see if I can sleeve one but I don't think there's enough meat to be able

A tasty package.
First off , cover the quill oil feed with the timing chest, its delicate and get knocked eccentric easily.
There is a critical dimension to check for the head with the new inlet valve, its valve spring end tip to alloy at spring seat, the big inlet valve can sit to proud if the seats are not cut deep enough , causing piston clash. Will dig through my notes for this.

push rods are easy, short ones ( inlets) go to outer cam lobes,

Clutch , strip the centre hub right down, drill out the pop marks on the screws first, look for wear at spider and endplate. replace cush rubbers if wear is light, otherwise a whole new centre is the easiest fix.

gearbox, shim to layshaft DS end, look for 0.003" end float. test assemble cluster in cases, pull /push llayshaft end, 3 thou is just perceptible, any more , clunk or click needs a thicker shim.

Cool.

I have new cush drive rubbers lying around somewhere but didn`t get round to trying to swap them out after seeing what a ballsache it can be and sort of forgot about that......

I wasn`t aware that I could buy a complete cush drive assy, so thanks for the tip on that. I have a couple of mates that have complete SRM clutch but what is the advantage over a well maintained standard clutch?

I have an alli pressure plate that came with the bike.

The SRM clutch will be the 7 plate conversion and the lifting plate, good mods but if you really want to improve it, around 500GBP will get you a Bob Newby belt drive, the plus side apart from running without oil is that you will never need to look at it again.

Gavin, they look like later 40mm valves to me (not the 43.5mm), If you use the bike in the intentions a metise was made for then I'd have suggested lower gearing and advancing the camshaft position by 1 tooth. It would give a lot of bottom end and still pull the ton... I am guessing though that your using it on the road?

if the stock 3 spring clutch has decent flat plates and a fresh centre it just about copes without cranking the springs in too tight.
New clutch centres are ~£100, just get one , odds are the old one is well worn. Un notched fresh splines and no wear on the end plate helps a whole lot.

Seven plate kits are available again another £ton, havnt heard a bad thing about them, one just came in the post for my bike today, the friction plates are thinner by about 40 thou each ( .110" versus .154" for the 6 plate) so the stack height ends up the same, these work with 650 springs , folk that fit them get a good light non slippy clutch. 6 plate stack (6 x150) + (6 x 80) =900 + 480 = 1.380 " , 7 plate stack ( 7 x110) + (6x80) +75 ( new plain) = 770+555 = 1.325, thinner!, good , because its tight in there. the only down side I see is the low fat friction material, theres not much to wear away to FA.
Most important to check your flat steel plates, any warp is a fail, test by putting on a dead flat surface then go round with a 2 thou feeler.

Inlet valve crit dimension, from spring seat base bare alloy to valve tip, should be 1.730" - 1.750", more is OK, shorter means it might say hello to the piston and be coil bound, my head had to go back to SRM to be corrected, hopefully they got it right for you , I found out when it was being checked for valve timing so no harm done.
if you got new springs to match your valves from SRM you will find they dont match the book dimensions, make a note in case you check them later and think they have grown/ shrunk if compared to book values. they work fine, nothing to worry about, I called Geoff when I measured them and the dims were different , he explained that the new spec springs are not the same but work fine.

You pretty much went all out with this engine, looks nice.

Thanks so far fella's....

Apart from SRM, who makes complete clutches (good)?
I'm not really sold on belt drive and I prefer to buy from Europe from a real dealer who deduct vat before sending to Norway.

The Bob Newby whilst being a belt (I think he does a chain version too) is a different belt To that used by the Tony Hayward clutches etc. I did a lot of searching when I went for mine, in the end I found guys like Push Rod Tom uses them on his bikes and decided to go the same route, the bike sees some
Hammer and hasn’t let me down yet, and whilst being a 6 spring clutch is still quite light. 2 friends have since fitted them and more than happy with them. I’m not on some kind of kick back for these by the way, but put a lot of mileage on my bikes and prefer to have something reliable that I can fit and forget. I also change gearbox sprocket sizes quickly also.

Norman Hyde for 7 plate clutch kit, the one I just got from grins triumphs is branded " Aerco". Plenty folk selling these kits in the UK, probably in Europe too.
Burtons ( BBB) sell complete clutches,regular or with an alloy plate option , not heard anything good about the alloy basket.
possibly a few others , its the same clutch parts as a triumph 650/750 twin apart from the triplex basket so a few options exist, but if you are changing the whole thing, new basket means new chain and front sprocket , fitting old to new is not a good idea.

I have bought a new primary and drive chain and full set of sprockets so that's why I'm thinking that now is actually the cheapest time for me just to plump for a complete new clutch

I am warming up to a newby but I'm a little concerned that my rotor won't work on it though. I'm running an electrex word 12v kit and having to fit another ignition would seriously bump up the price, especially now that it would make my triplex chain and front sprocket redundant.

Back and forth, back and forth.....

So, Realy my best/cheepest option is a new cush drive, springs and a 7 plate conversion?

You have new chain and sprocket , then it makes sound economic sense to fit a new clutch basket, you may be able to get an option for a whole clutch without plates , if you want to fit the seven plate upgrade, Whatever way you cut it a whole new clutch will be approx £300, new plain steels are usually a good idea, once the cush centre wears and slip is induced the plain steels warp with heat.
. if you already have the alloy pressure plate then buying separate centre and basket may make sense, tough call. I am envious of the Bob Newby set up, however it comes with its own issues, the primary case needs moved out, and ventilation is a good idea, dry belts need cold air, , on an off road bike which might end up lying in a watery puddle , maybe not such a good thing.

Sorted.

I found a basket from a nos parts dealer, here in Norway.

Ended up with the 7 plate conversion kit from BBB, new rollers , center and SRM pressure plate kit.

But like you pointed out Gavin, I should have just gone for the whole clutch with 7 plate conv. for what turned out to be the same price.

haha.

I have also belt envy but it does seem its not without some niggles. Even more so If I had to shell out for a new 12v system

Manx, can you post a photo of how your ignition should look when fitted?

for the standard alternator the Newby comes with the correct spacing to move everything outboard slightly. Can't see why it wouldn't work here also.

RE the alloy basket, I found the one I had to be very good and strong, My problems stemmed from the clutch centre and primary chain but the basket showed very little wear on the teeth or the tacks the plates run in.

The rotor sits on a washer and cone, up against the sprocket.





It might have been doable by just using a fatter washer?

I decided to upgrade the clutch a little and I am waiting for new gearbox bearings.

Motor is in the frame now at least.



I bought a new clutch basket and cushdrive, new springs, SRM pressure plate and a 7 plate conversion kit.

While I am waiting for parts I think I will start on the top end.

I know this has been done to death and Iv`e read quite a few threads on the subject but I am still non the wiser.

I have first oversize 79.5 pistons, what should my piston to bore clearence be? I have read that clearence should be bigger on lager bore but a concrete number would help more.

Also what should the ring gap be?

Cheers,
Rob

If you bought the pistons from SRM , better ask them,this clearance depends on the alloy mix used in the pistons ( Low ex silicon alloy can be a little tighter) my old iron barrels were 0.0045" clearance when rebored.
Ring gap, book says 0.008" - 0.013", I use 9 top, 12 middle , 9 oil ring, a wider gapped 2nd ring is meant to help seal better, better loose than tight here.
Important to get bores finish honed with a 150 -180 grit hone, this is a lot ruffer than most modern stuff, make sure the reborer uses this or suffer poorly seated rings.
This comes up a lot , google "britbike forum bore honing" or such like and read what John Healy says about it.,

My head was the same, I spent ages de masking, removing the step around the inlet faces, nerve wrackingly close to the valve seat , dremel and small burr.

What is the advantage of removing the step?

I`m clueless but pretty handy with a dremmel on 2 stroke ports.

ok, will do!

Clearence recomended by SRM is 0.0045, like you said Gavin.

I came home ready to fire up my dremmel but the dark bits on the head are just dark bits, there is no recess or edge around the valves.