Crank end thrust?

[Don G]

So here is a question that I could not find an answer to in any manual that I looked in, including Guzziology. What is the maximum permissible end thrust spec. for a round fin big block? I have had lots of experience building high performance GM etc. engines, those typically ran.008-.010 end thrust especially if equipped with a manual trans, what is Guzzi's spec?   DonG

[Don G]

OK! I am only hearing Crickets. LOL Lets try this a different way, Could someone supply the dimension of a new bearing? Like how thick it is across the thrust surfaces, then I could compare that dimension to my bearing, cuz I am thinking .024" is a little too much clearance.  Thanks  DonG

[rodekyll]

I have never found a thrust value for the big block.  I'd think that more is better than less on an aircooled engine, but I have no idea if 0.024 is good or not.  Personally I've not given it much thought.  Did you measure with the flywheel and crank gear in place?

[Don G]

Indeed I did, crank gear on and pulley hub, nut drawn up tight as well as the fly wheel. I figured that I may as well check the thrust incase there is not enough, would be nothing worse that buttoning the engine up and finding out that it wont turn! This is that V700 I am working on, the original crank had a botched sludge trap plug repair, I found another crank on EBAY for cheap and was doing a mock up as I am installing 83mm cylinders and Ambo pistons, I will have to check the deck height when my cylinders come back from the machinist. I sent the nice folks @ MG Cycle an e-mail asking them if they could supply me with dimensions of a new bearing, hopefully they respond.  Thanks  DonG

[Antietam Classic Cycle]

The new front main bearing I just received this morning is almost exactly 35 mm "thick" (34.99).

[pete roper]

In all honesty I think it’s easy to worry too much about the end float. I too used to worry, a lot, about it but at the end of the day you pretty much have to rely on the front main journal and the bearing/thrust face having been machined properly as it’s these that set the end float. Make sure the thrust face on the crank is undamaged, if it has been reground pay particular attention to the radius in and make sure as little as humanly possible, if anything, has been taken off the thrust face.

The most important thing is that the crank can’t move too far forward or back so that it imposes side loading son the rods. Given the amount of tolerance built into, most noticeably, the rod to piston clearance on the gudgeons it’s pretty clear that unless there is literally millimetres of end float the whole lot can whizz and flop about pretty much with impunity! 24 thou is pretty wide. 12 to 18 is what I usually think of as *Normal*. But as long as nothing binds as it goes together I reckon it’ll be fine.

Pete

[ray bear]

Im with peter, just imagine that you never checked that measurement just so long as there's  some float evident, when rebuilding my V7 sport that had only done 47000 mile..(chrome bore issues) there was around 9 t0 10 thou end float with the old bearings and when installing the new bearings around 8 to 9 thou. Also having been a mechanic all my life I was a little concerned being air cooled   but it had already done 47000 mile with a similar  clearance with no problems so I put it back together as is and that was around 3000 mile ago, One sweet sport.
After all what can you do about it, machine crankcase housings, machine rear of bearings, crank thrust ?? that's all rocket science and its not a Ducati,  put it back together and recheck it in another 50000 mile, Im sure it will be fine .
As with Charlies bearing my old front was 34.97 and the rear around 49.97 less gasket.    Bill

[jacksonracingcomau]

Perfect by design, nearly unfugable by halfwits
Onyer Mr Carcano, my hats off, never seen one anyone has managed to destroy by interfering
Bottom end is unburstable, same to this day afaik

[Rough Edge racing]

I don't know about a Guzzi, but .024 " in an automotive engine is excessive...  really excessive

[pete roper]

Perfect by design, nearly unfugable by halfwits
Onyer Mr Carcano, my hats off, never seen one anyone has managed to destroy by interfering
Bottom end is unburstable, same to this day afaik

.
Slightly different Martin in the fact that to save money they made the front main a pressed in, non replaceable, (And so far we haven�t been able to find a financially viable way of replacing it.) sleeve rather than a separate flange and the thrust face is a separate part keyed to the case in a similar way to the small block system but full circle.

When I get my original case back I�m going to experiment with using one of the earlier front mains and machining the case to fit it. All the bosses etc. are still inside the timing chest wall. It was purely another case of Piaggio cheating out. It�s fixable.

Pete

[Rough Edge racing]

 I find this interesting...Is the Guzzi crankshaft end thrust controlled by a single main bearing? Or is the crank trapped between the front and rear mains? If the crank has excessive thrust, do the rods have enough side clearance clearance not to be forced back and forth with the crank?

[pete roper]

Yup. Exactly that. End float is governed solely by the depth of the front main journal and width of the bearing. Rod clearance is fairly tight to control oil throughput for cooling and wedge maintenance but as I said there’s heaps of end float in the rod/piston clearance. At the end of the day the end thrust on the crank is only going to be the equivalent of the clutch spring thrust and that only occurs when the clutch is pulled in.

Pete

[oldbike54]

Yup. Exactly that. End float is governed solely by the depth of the front main journal and width of the bearing. Rod clearance is fairly tight to control oil throughput for cooling and wedge maintenance but as I said there�s heaps of end float in the rod/piston clearance. At the end of the day the end thrust on the crank is only going to be the equivalent of the clutch spring thrust and that only occurs when the clutch is pulled in.

Pete

 Type 247 BMW motors will run happily for a 100,000 miles with 10 thou of end float , can't imagine why a Guzzi motor wouldn't also . Same thing , the only real side force is during clutch disengagement . These aren't like old Brit motors where you can and most usually need to shim behind the main bearings to center up the crank , that had more to do with excessive machine tolerances than anything .

 Dusty

[Rough Edge racing]

  Dusty, crank thrust and connecting rod side clearances are often debated by experienced  high performance engine builders. I have seen examples of excessive crank clearance break up bearing  thrust surfaces on engines with too much clearance...And examples of bearing problems from too tight clearance...Some engine will get a noticeable knock from too much ,some not...
   
 

[Don G]

OK gents, thanks for the info and thoughts, I had another kick at the cat last evening, I pulled the timing gear off to check if it had seated all the way on the crank, I found that the O-ring between it and the crank was interfering with the seating of the gear, I don't know if it was the correct O-ring as it measured up as 25x3mm,part #90706250. Anyway once back together without the O-ring, end thrust came in @.008", bang on I reckon. Thanks Charlie for the dimension of the bearing, I will add that to my manual for checking out wear on used components.  DonG

[Antietam Classic Cycle]

OK gents, thanks for the info and thoughts, I had another kick at the cat last evening, I pulled the timing gear off to check if it had seated all the way on the crank, I found that the O-ring between it and the crank was interfering with the seating of the gear, I don't know if it was the correct O-ring as it measured up as 25x3mm,part #90706250. Anyway once back together without the O-ring, end thrust came in @.008", bang on I reckon. Thanks Charlie for the dimension of the bearing, I will add that to my manual for checking out wear on used components.  DonG

Info. on the o-ring:
http://thisoldtractor.com/moto_guzzi_loopframe__for_sealing_the_crankshaft_timing_gear_to_the_crankshaft_-90706250-.html

[oldbike54]

  Dusty, crank thrust and connecting rod side clearances are often debated by experienced  high performance engine builders. I have seen examples of excessive crank clearance break up bearing  thrust surfaces on engines with too much clearance...And examples of bearing problems from too tight clearance...Some engine will get a noticeable knock from too much ,some not...
   
 

 Tony , I've witnessed that also , especially on hot rodded HD and Triumph engines .

 Dusty