What to do with this TV175 engine?

[Storkfoot]

This is a Series 3 TV175 engine. It’s a bit battered but I suspect that is because it has been out of a frame for many years and occasionally thrown around a concrete floor somewhere in Italy. Inside the casing, it was generally in quite good condition, if a bit more seized than usual.

Anyway, on opening it up a couple of weeks ago, I discovered that the cylinder has been rebored to accept a 65.6 piston. This piston is no longer usable as the skirt broke off when I was removing the barrel which wanted very much to stay where it was.

You can see from the pictures that a few fin edges have broken off. I have the bottom edge which I may well get welded back on (the chain casing needs a couple of bits of alloy welding done anyway) so I believe it is usable even if the bore is a bit on the thin side.

At this point, I should throw in that I am going to use a GP crank with a 116mm conrod. The original TV crank was past its best. I also should add that I have to check whether in the inlet and exhaust ports have been altered. It looks like they may have both been opened up, if not enlarged internally. I’ll check this before I do anything.

If you have any thoughts on using this barrel, feel free to share them.

This leads me to what piston and cylinder head to use. Clearly, I am limited in what pistons to use given that the crown height of the TV piston is 30mm, not 39mm as usual. The original cylinder head is a bit too battered for my liking.

So, pistons. I have found three that could work:

(1 )

66mm, 30mm crown height Mugello. Two thin rings. This has a boost port cut into it but it does not appear to correspond with the transfer ports in the original barrel.

(2 )

65.8mm “old school” 30mm crown height piston. I haven’t seen this yet so I don’t know if it is 2 or 3 rings but I would guess that it is probably three thick rings.

(3 )

Suzuki TS185ER 65.75mm bore, 32mm crown height. Again, 2 thin rings.

(3 ) is by far the cheapest piston and has the added benefit of having a readily available 66.0mm piston, if needed. In the downside, it’ll need a 2mm (or thereabouts) packer and a remained cylinder head.

Cylinder heads, well, I may try and get a second hand GT, bgm or Mugello head as they’ll assist with cooling down a cast iron barrel with quite thin walls. Failing that, I have a 150 Innocenti head that has already been machined to accept a 62mm 175 piston.

Thoughts please

[Warkton Tornado No.1]

You appear to want to conserve that barrel - despite the likely issues of the bore - & although I’d agree that preferable to one of the Indian 175 replacements*, you should consider the option of an OEM substitute nearer to original bore size. Personally, if I felt that conserving that barrel was the remit, I’d get a cost for a sleeve. The Nikasil specialists for replacing motorcycle barrels will do this for you & match the ports. I had that done to save a good race Rapido cylinder & the result was excellent. It was about £140 @ that time.

I suppose, summarising the above, I would not be happy with such an oversize bore! If I were more of a salesman, @ this point, I’d try & talk you into buying the Ancillotti TV175 piston I have that is 66.2 mm, but it has no Dykes top ring & the other ring is as OEM cast iron.

Of the pistons mentioned, the TS 185 is by far superior & genuine Suzuki can be extremely cheap, appearing sometimes on the auction sites.

Finally, large block barrels can be made to fit. I’ve never done it, but if that were a consideration, then the small block kits should also be given some thought.



* the Indian 175 barrels can be made to work well, but that involves a lot of work. I tuned such a kit for somebody & the transfer ports in the cylinder wall took an age to match, tidy & ultimately flow. The castings are invariably chilled & meant porting progress was slow & a risk to even tungsten carbide cutters. The option was to use sanding drums with a 90 degree cutting head. Even when I felt that they were optimised, casting flaws were still prevalent. The same issues in the inlet & exhaust ports meant enlarging more than I would otherwise have done, but the performance was far better than a good, standard 200.

[Storkfoot]

Thanks for the reply WT1. I value your opinion.

You are not alone in advising that increasing the bore to 65.75 or 66 leaves the walls pretty thin. I had hoped that using a better piston, and a cylinder head with more surface area, would compensate enough to make it a viable option.

I was planning on simply using an Sh1/20 and either a standard exhaust or, perhaps, a 40 or 42mm Clubman with a 5.1 final drive ratio as opposed to the standard S3 TV 175 of 4.8.

I am in no rush to build this engine. I may source another TV barrel and try a smaller TS185ER piston.

Has anyone, in the past, successfully run a TV175 barrel bored to 66?

I’m not minded to fit a kit on this, much as I used to love my GT186 with a 115mm conrod.

[Adam_Winstone]

TV barrel at 66mm, yes, this is a conversation that was popular in Italy from 60s onwards.

Back around 1990 I borrowed Dean Orton's personal runaround, when staying with him and needing to visit local shops and scrapyards to source bits for my TV175 rebuild. Dean's bike was an LI125S (if memory serves correctly) that had a 175 barrel bored to 200cc, which I remember was novel because of concerns that the walls might be thin and prone to warping. However, that bike 'The Borsa' (The Bag... of) was constantly dragged everywhere by Dean, myself and others, without nipping or causing issue. As you mentioned, this was probably helped by use of standard carb and exhaust.

The TS185 Suzuki is certainly the way to go for performance and piston reliability but it all depends what you plan to use the bike for.

[Storkfoot]

Probably for UK rallies within a couple of hundred miles. That and general running around locally. I want it to replace a Casa 185 in my SX150.

[Adam_Winstone]

In which case you'll be looking at a downgrade in performance, unless you intend to tickle the porting, in which case I'd be looking at the Suzuki piston and rings. The Suzuki piston gives much more scope for exhaust port work without running into the issue of ring breakage.

[Storkfoot]

Thanks, Adam. I have no thirst for speed these days so that’s not a problem. Seizing the barrel regularly would be a deal breaker though. That said, a Suzuki piston, rebore and reprofile of an existing head wouldn’t cost the earth so I may try it but leave any modest tuning for now.

By the way, I haven’t got anything against my Casa 185. I have had issues with gearboxes and the crank (my error that one) in that engine but it has got up and down the country fine for the last couple of years. I just want to put that engine in my GP150 at the end of 2025.

Thanks again.

[Warkton Tornado No.1]

Although you have considered the piston options & taken into consideration the advantages as well as disadvantages, taking into account the variations in compression height of those pistons. Personally, I have long held the belief that a high primary compression is of no benefit. In fact, admittedly with much more modern two stroke engines such as, say, an air cooled Yamaha, it has been proven that simply by substituting the con-rod for a longer alternative with a suitable base packer, the power & torque both improve. These days, with the availability of alloy base packers in a large range of thicknesses, that really does make for much easier matching of the transfer ports - despite what some consider of little benefit - & enable the elimination of one of my other pet hates, the head gasket.

However, besides taking the opportunity to remind readers of my preferences ( ) there is yet another good ‘non-reed’ piston that starts @ 65 mm with oversizes that was available in forged or cast versions, though I only ever used them in single ring versions. I used them with either 18 mm wrist-pins or with flanged bushes without issue. The piston is the Polaris Indy which is still in wide use & consequently manufactured by Wiseco amongst others.

[Cgt75b]

What’s the plan then Paul, any thoughts?

I’m in a similar situation.

HNY btw.

[Storkfoot]

What’s the plan then Paul, any thoughts?

I’m in a similar situation.

HNY btw.

Happy New Year to you too, Paddy.

As I have said, I am in no rush at all. My priority is the engine casing at the moment. I can’t budge one of the swan neck studs or any of the seal plate screws. The endplate was fixed with bolts, two of which were M8 (the endplate has been drilled to 8mm too) and the dowel holes in the casing are both oval. Oh, and the chain casing needs welding too.

Top end, at the moment, I am minded to go down the Suzuki piston route with a reprofiled Innocenti cylinder head. I have found a cylinder head in the garage in decent condition. But, I am on the look out for a barrel that is under 64mm bore, so it can be rebored to match a TS185ER 64mm piston which still seem easy to source. I’ll leave the barrel untuned and gear it as a standard TV at 4.8 final drive.

We’ll see how it ends up. Probably nothing like what I have said above

[GExS]

I’ve a standard TV175 S3, and it’s still running great on the original piston. I’ve also done Suzuki TS185 conversions with TV175 barrels using 60x115 cranks, reworked head, and a small packer at the base of the cylinder to get the squish right, and I absolutely love the conversion with the standard carb (normally 22mm) and exhaust. The only issue I’ve found is the gearbox with the standard or Suzuki set up, with a final drive of 4.8 it won’t run well up hill or into the wind. Recently, on my standard TV175 I’ve put a Pacemaker box in running 46x17 get to a final drive ratio of about 5 and its transformed it to a far better ride.

[Warkton Tornado No.1]

What’s the plan then Paul, any thoughts?

I’m in a similar situation.

HNY btw.

Happy New Year to you too, Paddy.

As I have said, I am in no rush at all. My priority is the engine casing at the moment. I can’t budge one of the swan neck studs or any of the seal plate screws. The endplate was fixed with bolts, two of which were M8 (the endplate has been drilled to 8mm too) and the dowel holes in the casing are both oval. Oh, and the chain casing needs welding too.

Top end, at the moment, I am minded to go down the Suzuki piston route with a reprofiled Innocenti cylinder head. I have found a cylinder head in the garage in decent condition. But, I am on the look out for a barrel that is under 64mm bore, so it can be rebored to match a TS185ER 64mm piston which still seem easy to source. I’ll leave the barrel untuned and gear it as a standard TV at 4.8 final drive.

We’ll see how it ends up. Probably nothing like what I have said above

The stubborn fixing screws can present a real challenge, but copious soaking with penetrating oil or Derv will help. WD40 is a Water Dispersant & nowhere near as effective. Then, good drill bits @ a very slow speed as can be achieved with the better rechargeable drills, or preferably a pillar drill, should eventually enable a small pilot to be achieved, enabling gradual increases in hole size until the fastener virtually volunteers to come out. Sorry if you are already aware, but slow cutting speeds are essential to avoid the stuck fastener getting hot & hardening as the result. Toolstation or Screwfix sell some good drill bits that cope with just such a scenario. From memory, I think they may be hollow start….

Regarding the end-plate oversize screw holes, you should be able to return them to M7 via wire thread inserts (Helicoils etc) which I have done many times. Oversize dowel holes can often be got around my carefully drilling deeper for longer length specific 7 mm dowels to be fitted. Again, I have done that rather than try stepped dowels or bushing the holes as they are purely for location, important though, nonetheless.

I used to think the only bodging of Lambretta was done by us lot in the UK, but clearly that is not the case

[Storkfoot]

I’ve a standard TV175 S3, and it’s still running great on the original piston. I’ve also done Suzuki TS185 conversions with TV175 barrels using 60x115 cranks, reworked head, and a small packer at the base of the cylinder to get the squish right, and I absolutely love the conversion with the standard carb (normally 22mm) and exhaust. The only issue I’ve found is the gearbox with the standard or Suzuki set up, with a final drive of 4.8 it won’t run well up hill or into the wind. Recently, on my standard TV175 I’ve put a Pacemaker box in running 46x17 get to a final drive ratio of about 5 and its transformed it to a far better ride.

Thanks for that. I too have a standard TV175 Series 3 on a 62.2 bore. I haven’t noticed the need to alter the gearing but I tend to use it for running around locally.

An RD400 115 conrod on a 60 crank is interesting. I have run an RD400 conrod on 58 webs before and they are very sturdy conrods in comparison with a Lambretta 116mm. As I need to replace the crank anyway, I may well go with that.

[Storkfoot]

The stubborn fixing screws can present a real challenge, but copious soaking with penetrating oil or Derv will help. WD40 is a Water Dispersant & nowhere near as effective. Then, good drill bits @ a very slow speed as can be achieved with the better recharg, or preferably a pillar drill, should eventually enable a small pilot to be achieved, enabling gradual increases in hole size until the fastener virtually volunteers to come out. Sorry if you are already aware, but slow cutting speeds are essential to avoid the stuck fastener getting hot & hardening as the result. Toolstation or Screwfix sell some good drill bits that cope with just such a scenario. From memory, I think they may be hollow start….

Regarding the end-plate oversize screw holes, you should be able to return them to M7 via wire thread inserts (Helicoils etc) which I have done many times. Oversize dowel holes can often be got around my carefully drilling deeper for longer length specific 7 mm dowels to be fitted. Again, I have done that rather than try stepped dowels or bushing the holes as they are purely for location, important though, nonetheless.

I used to think the only bodging of Lambretta was done by us lot in the UK, but clearly that is not the case

I have tried penetrating oil and blow torch heat. Not one of the four is even budging. I have just walked away from it for the time being.

The endplate. It appears to me like the oversized dowel holes are a relic of before the m8 bolts were put in as a remedy to a loose endplate. Ignoring the dowels, the endplate is a good fit with the Layshaft and gear cluster and there is no evidence of the M8 bolt heads catching the chain. I don’t like bolts being screwed in and out of alloy so my plan is to replace them with studs, including the M8 ones. The dowels, I think I may have a couple of M8/M7 stepped ones so I’ll look onto whether I can use them first.

[Adam_Winstone]

Are you using an impact driver in combination with the heat?

[Storkfoot]

Are you using an impact driver in combination with the heat?

My impact driver is too wide, so it catches on the mag housing face. I also don’t have the correct sized bit to engage with the slot in the screw. All in all, it’s pretty useless

If anyone has a recommendation for an impact driver that is good at getting these screws out, I’m all ears.

[Warkton Tornado No.1]

Are you using an impact driver in combination with the heat?

My impact driver is too wide, so it catches on the mag housing face. I also don’t have the correct sized bit to engage with the slot in the screw. All in all, it’s pretty useless

If anyone has a recommendation for an impact driver that is good at getting these screws out, I’m all ears.

It’s worth a try with the kind of impact driver that you clobber with a lump hammer so are you sure that the one you have is incapable of reaching? I have @ least one of the reversible type that is 1/2” square drive & the bit holders are removable. That means a 1/2” square drive extension can be fitted twixt the main body & the bit holder, thus allowing access to the stubborn screw head.

Fasteners stuck in place & their removal is a science, I reckon, as I find that even when they start to move, you can still get caught out. So, these days, I find it best to keep alternating between ACW & CW in an attempt to nurse the things out. Often, just to get the things moving I have resorted to trying to move them clockwise, even though it is counter-intuitive.

I thoroughly understand the intent to conserve the seal plate but ultimately, you could hardly be blamed if you resorted to grinding the heads & fitting a replacement. I would bet most of us have more OEM steel plates than we could ever use If you haven’t I’ll gladly donate one of mine & post it to you.

[Adam_Winstone]

^... like

[Storkfoot]

I had a further look for a correct sized bit to properly engage with the slot in the screw and, yes, I did have one. Three minutes later, all four screws were out. No heat needed although I did have to be very careful to keep the impact driver away from the mag housing edge

[Warkton Tornado No.1]

Well done in extracting those horrible M6 slotted countersunk screws The fact that socket head drive screws were used elsewhere in the OEM build makes me wonder why the factory persevered with the labour intensive process involved in using such screws, necessitating the centre dotting of them as the means of locking them in place. Good SCHS (Socket Countersink Head Screws) such as GKN, Holokrome & Unbrako are ideal replacements, though I doubt such quality products are obtainable via many of our so-called specialist suppliers.

That prompts me to mention that the end-plate fasteners comprised M7 rolled thread studs with hardened half- height nuts & hardened spring washers which I doubt would be supplied by such suppliers either…..