Iggy’s 251 engine build is more of a Carry On than Sid James’ laugh. Today we finally get to close the casings.
You can catch up on the first three parts of this series by clicking on the images above.
If you read the earlier episodes then you know that the bearings are in place and the primary drive is rebuilt and fitted. The next step is to pull the gearbox into position. Before that though, we need to delve into the murky world of rear hub oil seals.
Oil Seal Options
Like late Vespa PX casings, the Pinasco 251 casing has the capacity to utilise an internal oil seal (27-42-10) running on the output shaft.
Early PX layshaft (left) and later version (right) with parallel section for use with internal oil seal.
Piaggio casings for internal oil seal, with drain hole indicated.
SOLUTION A: If you use an oil seal inboard of the bearing, then YOU MUST use the matching layshaft with the parallel section for the oil seal to run on. Additionally, YOU MUST also use a self-lubricated rear hub bearing with two rubber seals (suffix 2RS) because the inner oil seal means that gearbox oil will not reach the bearing to lubricate it.
SOLUTION B: Alternatively, it is possible to omit the inner seal and use the old system of an external (to the bearing) oil seal running directly on the rear hub. For this system to work YOU MUST fit the correct seal to match your rear hub. Hubs come in 3 flavours:
• Hubs with a boss measuring 27mm are the oldest, weakest type and match with an 27-47-6 oilseal.
• Hubs with a boss measuring 30mm are stronger and work with the oilseal 30-47-6.
• Hubs with a boss measuring 31.5mm are the latest type and intended for use with a fibre dust seal, in conjunction with a sealed bearing and the internal oilseal. The surface is not ground to match a seal.
The external seal options: (top) oil seal for 30mm hubs, (left) oil seal for 27mm hubs, (right) dust seal for 31.5mm hubs.
ONE TO WATCH
The Piaggio casings that accept inner oil seals have a small drilling in the casing which will let you know about a failed seal because gearbox oil will drip out of the bottom of the casing. The advantage of this drill-hole is that oil can’t get past the bearing and into the rear brakes, but instead it leaks on the floor and potentially onto the rear tyre. The big disadvantage of the inner oilseal set-up is that if the oilseal fails (which isn’t common provided that the gearbox oil is changed regularly) then the engine must be completely stripped to change it.
ANOTHER WAY: If the internal oilseal has gone on your engine, but the rear hub bearing is fine, then you could clean out and plug the hole in the casing by tapping a thread in the hole and thread-locking a bolt in to seal it. This will prevent loss of your gearbox oil but eventually oil may seep through the seals in the rear hub bearing and contaminate the brake shoes. The solution then is to fit a matched rear hub and conventional oilseal.
ONES TO WATCH
If you fit a conventional rear hub oilseal to an engine fitted with a sealed rear hub bearing then in theory no gearbox oil should pass through the bearing. In this case, the lip of the rear hub seal should be thoroughly greased to prevent it running dry and wearing out prematurely.
Ignore Viton-peddlers who charge a premium for packs of Viton seals covering every position in an engine. Viton is only helpful where the seal comes into contact with ethanol-rich fuel. Since the rear hub oilseal should only contact gearbox oil then there’s no need for anything fancy here.
What did we do?
For Iggy’s engine, we re-used the Piaggio layshaft from his old Malossi 210 donor motor. This was a late type with the parallel section for the oil seal to run.
Given that we had a sealed rear hub bearing, we could have fitted the internal oilseal but the oilseal set on hand did not include that type. Instead we fitted the 30mm external oilseal to run directly against a rear hub with a 30mm boss. This seal lip was greased to prevent wear.
Pulling the layshaft into position using a tubular spacer and the hub nut. It is also ok to knock the layshaft into the engine but you must use a tubular drift and take care not to touch or damage the gear selector rod.
If you pull the layshaft into position with the hub nut then you can use a spanner in the selector slot to hold the shaft still. Rotate the gear assembly as it enters the casing to ensure correct meshing of the teeth.
VIDEO – Fitting the layshaft and loose gears.
The Pinasco 251 Slave engine uses a balanced bell-shaped crank with a splined drive connection to the clutch.
Crank Fitting
When I was young I used to tap crankshafts into the drive-side main bearing with a copper hammer. That’s not a great idea. Having seen how cranks are trued – essentially whacking the webs with a great big copper hammer – it became apparent that hitting cranks with anything is not a very good idea.
My solution was to make a tool to pull that crankshaft into place, using an old Sundance handlebar grip.
Sundance grips are useful for many things; just not as handlebar grips.
Simple crank-fitting tool. Commercial tools to do the same job are also available from the likes of SIP and Scooter Center.
This tool is simple
A Sundance grip with a 12mm hole in the end.
• A piece of M12 stud with an M12 x 1.5 (clutch) nut welded to the end.
• Another M12 nut and a washer.
You can see it being used on the video below.
VIDEO – Crankshaft Fitting
ONE TO WATCH
Sundance grips are chrome-plated aluminium. Be careful that the chrome does not flake off and end up in the bearings when used as a drift or a puller.
Pulling the crank into the engine for the first time…
What did we forget?
When we first fitted the crankshaft we realised that the inner race for the flywheel side bearing wasn’t fitted, so the crank had to come out again. Doh!
There are now professional drift tools for the job of fitting bearing races. There are also wedges to support the crankwebs from being bashed together when you tap the bearing race onto the crank. Having said that; our trusty Sundance grip also does the trick perfectly.
It’s easier to fit the race if it is warm and has expanded a bit but avoid heating directly with a flame which can soften the bearing. Dropping the bearing race into a cup of freshly-boiled water is enough to expand it so that it slips on most of the way. The water quickly evaporates when you remove it from the cup and the hot race takes very little force to tap the rest of the way home.
Mind the gap
The temptation here is to knock the bearing inner race (also called a track’ or ‘sleeve’) fully home until it stops. If you do knock the race all the way to the stop then it’s not a problem; the bearing will still function fine, but you are kicking another problem into the long grass for a future rebuild. Without a small gap of around 1mm between the bearing race and the shoulder on the crankshaft it makes life very difficult for an official Vespa bearing puller to be used.
The old, recommended way to achieve this gap is to use two 1mm feeler gauge blades as spacers to prevent knocking the bearing on too far. In reality, holding a crank, two feeler gauges, a bearing drift and a hammer requires the dexterity of an octopus.
A special spacer (‘distance gauge’) is available from dealers such as SIP that allows you to tap the new collar into position while still leaving the recommended 1mm distance to the crank web.
TOP TIP: It seems a bit much to get a special tool simply to act as a spacer. Instead, you can do the same job simply by twisting a length of 1mm MIG welding wire around the crank before you fit the collar. This is easily untwisted and removed after the collar is fitted.
What Next?
After fitting the kickstart mechanism (don’t forget the kickstart shaft O-ring) and spring, the casing was ready to fit.
As mentioned previously but worth repeating, only the two tubular dowels are used to align the casing NOT any dowel at the rear of the casing.
We used Threebond 1215 silicone as well as the supplied Pinasco paper gasket and bolted the casings together using new bolts, studs and nuts.
TOP TIP: If you are buying an engine like the Pinasco 251, which uses a unique crankcase gasket, then it’s worth getting a spare gasket set in case you damage one during assembly, or if you need to open the engine again at a later stage.
This engine also uses T5 casing bolts to hold it together. We were short of 3 longer studs so had to nip to a local scooter shop to get some.
The Pinasco gasket is a ‘closed’ type across the crankcase mouth, so after the cases are bolted together the gasket needs considerable trimming.
After the gasket was trimmed with a scalpel the cylinder gasket face was reassuringly flat.
Text: Sticky
Videos and main images: Iggy
Additional images: Sticky and SIP Scootershop
Thanks
Thanks for help and assistance to Alan at Diablo Moto, Dan at Total Revamp, Christiaan at PLC Corse and Piergiorgio and Vittorio at Pinasco for help with this article.
NEXT TIME: We fit the top end and begin the leak-down test process. Place your bets in the comments below about whether or not it seals at the first attempt… Read about it here.
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