Crank end float

[rolf j]

In Pete Ropers Engine Strip series he mentions 6 to 12 thou (0,150 to 0,300 mm) as a good end float, should not be larger at least. However, as he points out, Guzzi has never specified a value here.

I ended up at 0,050mm in my tonti bigtwin engine (racing), and I wonder if the risk with such a tight fit is acceptable? What could happen? I cannot see there should be any gap for e.g. oil flow required at this place? Anybody with experience on this?

[Guzzistaracing]

Hello Rolf, Is there a risk that it could get too tight from heat expansion?

[pete roper]

That is very tight. Yes, the oil has to be able to escape. One of its two main functions is to remove heat.If the flow from wherer the bearing is working is inhibited you'll end up cooking the bearing. On a race motor you want to have the tollerances at their wide end. Not their tight end!

Pete

[rolf j]

That is very tight. Yes, the oil has to be able to escape. One of its two main functions is to remove heat.If the flow from wherer the bearing is working is inhibited you'll end up cooking the bearing. On a race motor you want to have the tollerances at their wide end. Not their tight end!

Pete

That will be the front (timing end) bearing suffering in this case,...right?

[pete roper]

Yup. which reminds me? You wanted a sloppage sheet for this thing didn't you? send us yer mailing address again and I'll pop one in the mail. I did another run of 'em and they are back on the shelf.

Pete

[rolf j]

Pete: See PM.

It appears to be two slots behind the front wall of the casing where the crank runs (insite the casing). Aren't they for escape of the oil from that bearing, so that end-float perhaps becomes less of an issue? (Just clinging on to a hope for not tearing apart the sorry ol'lump YET another time!)

rolf j

[lucky phil]

No experience with Guzzi crank end float but I have some with Ducati engines.A set of Ducati cases will expand around 0.3mm between the main bearings when heated to operating temp and the crank will expand around 0.15 between the Journal faces.So as the engine heats up the cases expand more than the crank and the end float increases.This is why you preload Ducati cranks these days by about 0.3 so when hot the there is just enough preload to keep the angular contact mains loaded.
Cant see why a Guzzi crank and cases would differ significantly in their response to heating up to operating temp.
Obviously with plain mains a Guzzi crank would need to start with some end float but I'm confident as the engine temp increases the float will increase as well.Whether it will be to little when hot I dont know but if you start with 0.05 then Id imaging when its hot it would be around 0.30 or so,at an estimation.
Friend of mine is building a Guzzi engine for racing and converting the rear main to a pair of angular contacts back to back to try and loose some of the friction from that massive bearing.Will be interesting to see how it goes but he wont have any back to back dyno data to prove the mod.
Ciao

[rolf j]

Thanks for your views, Phil! I am quite puzzled about the theory and practicals here. The back main in a Guzzi is totally floating so the heat expansion being interesting here, as far as end float is concerned, should be only the front bearing itself, made of aluminium. I.e. a hotter bearing becomes longer and fills inn the distance between the sprocket and the krank. I reckon the steel crank will expand only marginally compared to the bearing.

To cut the story short about the practicals:
The end of the story in my case was a total disaster and the end of the front bearing was ground up after 2 very short passes on the racetrack. Smeared out aluminium was seen by the oil slots on the inside and melted aluminium sticking to the back of the sprocket on the outside. Not pretty. I'll be starting on fresh again to rebuild the engine, but meanwhile I've built a 948cc engine from the spoils of the disaster and whatever could be found in the shed. Seems to work well while waiting for the new one.

rolf j

[pete roper]

Rolf, I'm sorry, you just keep slipping off my radar. I'll get an oil pump and sheet off to you along with some main bearings if you like, I've got lots that are serviceable. Slots on the back of the front main are the thrust face for the crank designed to allow it to take the side loadings imposed by the clutch pushrod. Yes they let oil escape but its how they let it escape that is important!

Pete