Bridgestone Motorcycle Parts Discussion Board

Bridgestone Tech Talk => Engine => Topic started by: bs_doug on December 27, 2008, 12:26:56 PM

Title: Mag Dynamo Rebuild, crank bearing seals
Post by: bs_doug on December 27, 2008, 12:26:56 PM

This is my first post and look forward to sharing my Bridgestone experience and memories with you people.

My 350 GTR restoration is under way. After pulling down the engine (because I found all kinds of gasket cement on the cases, and wanted to see why the engine was opened) I found a few problems.

The oil seals on the crank must have been replaced and one side seems to have rubbed on the case. There is no damage but the seal that has been secured into the flywheel recess by center punching the flywheel around the perimeter, appears to have come out of place at one area.

Question: What is the correct procedure to install these seals and can I corect this problem?

The Mag Dynamo bearings are shot and I can't get the clutch side bearing off. I suspect pounding on the shaft will result in a broken case.

Question: I plan to remove some material from the snout of the bearing holder so I can get a puller around the bearing and pull it off rather than pounding the shaft through the bearing. Sound reasonable?

What a great engine to work on. I am thoroughly enjoying working on this bike. I ahve a running 90 Sport and a none running hurrican to work on after the GTR is running. Please advise on any experience you have with this 350 engine and tips to rectify the problems I found above.

Thanks for the help,

Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: czmike on December 28, 2008, 08:49:11 PM
Hi Doug,

I haven't overhauled my GTR's engine yet so my "two cents" worth below should be checked out with others who have more experience & knowledge however, I have looked inside one and at a dismantled crankshaft so I can't resist a comment or two:

Why do those previous owners use so many different kinds of sealant?

Surely the crankshaft cheek oil seal (the thin, large diameter one) that has come out has done so precisely because it was staked in place. I don't think this technique would have been applied by Bridgestone during original manufacture as it will damage the sealing region in the crank and distort the seal's thin flange. This would destroy any possibility of a good pressure seal while encouraging the seal to release its tenuous grip on the shallow recess in the flywheel. I think the integrity of these seals under pressure is important as they appear to help maintain the oil pressure as well as direct oil flow from the injection pump to the rotary valve's sealing surfaces and the connecting rod bearings (the "big ends").
I think I will be fitting mine with a, yet to be made, seal installation tool. This will be a ring of appropriate diameter that is a good fit in the seal's shallow channel and will permit the application of sufficient insertion force to be applied evenly and squarely around the fragile seal rim without any distortion occurring (there might be a PVC plumbing pipe of the right size?). An appropriate sealant applied to the seal rim would also be a good idea I think. I would use a small amount of old style "Aviation Gasket Cement". Permatex #3, non-hardening is my favourite for seal installation.
This sealing arrangement is unusual and its purpose appears misunderstood by the writers of some articles I have read about the GTR engine. They are not crankcase gas seals at all (there is only one of these necessary, at the drive gear end) but oil control seals.

That "Mag Dynamo" is actually an Alternator (or AC Generator/Dynamo if you like).
Its neat isn't it and does look like a Mag-Dyn or some such. Pity it doesn't have a little more output though. Have no help for you with the bearing removal yet but hitting small things with big hammers is never a good idea I reckon. This sort of engine responds better to a bit of thought, like your suggestion, rather than brute strength. They are products of Japanese culture after all.
I have a few of these alternators so I'll look at one tonight (I'm at work at present) and see if I can offer an opinion. I've embarked on a project to fit an electronic replacement for the ignition points in one of these so no time like the present to get acquainted properly.

Let's know how you get on please Doug.

Best Regards,

Mike Munday,
Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: bs_doug on December 29, 2008, 09:04:02 AM
Thanks for the advice on the seals. I will pull the bearings to see what's going on there. This GTR was some ones source of parts for a race bike. It came with all sorts of modified parts. Rotary valve covers with enlarged intake, one with a Amal TT carb flange) shaved heads, Ported and raised barrels, an empty generator with only the shaft and points (no coil), clutch cover with numerous, meticulously, drilled holes  for cooling. A lot of crank pins and rod bearings. Alas the expansion chambers were sold seperatly as were the TT carbs. Someone was serious about racing for sure.

Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: Bridgestone Man on December 29, 2008, 05:34:34 PM

Tapping out the Mag Dynamo bearings is no big deal, just strip unit, heat up bearing
with a small torch and tap out with a brass bar, works pretty good

Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: Jeff Bar on December 29, 2008, 06:49:20 PM
Doug and Mike, are you aware that you do not use the thin large seals that were installed from the factory?
I am taking about the two that are about the thickness of a quarter but around 4 inches across?  They
were deleted from the factory service papers

Jeff Bar
Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: bs_doug on December 30, 2008, 08:10:54 PM
What is used instead? I read the service paper on it where it says to not use them, but I thought that later it was revoked.

Can you clarify. I'd like to toss the miserable things if they are unecessary.

Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: czmike on January 04, 2009, 09:50:22 PM
Hi Jeff & Doug,

In Service Letter # BSG-0070, entitled BRIDGESTONE 350 GTR ENGINE REPAIR (Service Letters are available in the Downloads section, this one on page 43) it says under CRANKSHAFT END SEAL REMOVAL: “Do not reinstall new end seals. [ed.; This instruction was later reversed. End seals should be installed.]”

I don’t know if the Editor’s note was inserted at the time by Bridgestone or much later by others but it sounds fishy to me. We would much prefer a clear instruction wouldn’t we. Why confuse the issue with the Editor’s note? Why not just change it to the new intent or publish a new Service letter?

If you analyze the motor internally and reverse engineer it a little the function of these seals appears to me to be important for oil control in the bottom-end of the motor. Perhaps others who have had big-end failures would like to comment on whether crank end seals were fitted or not at the time and whether they appeared to be functioning or not following tear down. I have read elsewhere that they come loose, as Doug experienced, so maybe Bridgestone messed up with the design of the seal retention as it does appear to be feeble. With only this ambiguous document to go on and no physical evidence, as yet, I plan to fit these seals and enhance their retention by means other than staking. Three small screws (M3) installed into tapped holes in the crank wheel might be a good approach I think. I will also be attempting to establish a pressure test to be applied at the crankcase oil fittings on an assembled motor. I think the existence or otherwise of end seals (or their sealing integrity) will show up in such a test. Preliminary tests show that pressure in the oil gallery of the crankshaft, feeding the big ends, will be easily measured there. Of course I need to find out what the normal range of pressure at that point should be. This fits in with my dream of fitting warning indicators to the oil injection system.

Best Regards,

Mike Munday
Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: bs_doug on July 21, 2010, 09:31:22 AM
Hi Mike,
How did your modification turn out? Where did you buy the seals?
Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: reed on July 22, 2010, 07:08:46 PM
BS Doug
I have pulled down three Bridgestone 350 gtr engines and the crankshaft endseals were all removed!
And bear this in mind 2 engines were still using the oil pump and 1 was pre mixed and all crankshafts
were in tolerance.
Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: disc_valve on July 23, 2010, 02:20:34 PM
I can't add much to the debate on the crank side oil seals, except to say that I've been running my 1968 GTR with these seals removed since 1987. The bike has probably done around 18,000 miles in that time and so far here is no sign of any crank problems. I run it with the standard oil injection pump set as per the factory spec. I don't thrash the motor in deference to the 42 year-old components whirling about, but I'm not afraid to use the go-stick when the mood takes me.

Having said that, maybe the crank is due to fail next time I take the beast out, but it's never shown any signs of trouble - and it smokes like a good 'un.

Another thought about your generator bearing. I've stripped a couple of generators in the past - in one case to fit new bearings - and I can't remember having any serious trouble getting the old bearing off. From memory, I just undid the two external through-bolts (THEY were tight!) and the end case came away complete with the shaft assembly. You have to remove the ignition cam at the other end to allow the shaft to pass through the point side casing. I have a vague memory, though, that there was a circlip inside the clutch end case holding the bearing in place. It might be wise to double check for that before attacking things with a puller or pounding it with a hammer!.

Hope that's of some use,

Graham Weeks (U.K. Member).
Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: BS Mechanic on September 19, 2010, 06:07:51 PM
Just my thoughts on the crankshaft oil seals:  They were most likely "designed in" in the early stages of the design, as a "good idea", and as a marketing theme.  It sounds like a good idea to  control the oil going to the rod bearings, and it makes good advertising copy.  As the engineers found out later in production, once warranty claims started to come in from loose seals tearing up the insides of otherwise reliable engines, and like any other 2 stroke, the motor will perform just fine without the seals. 

The "ed. note" referred to, which says the seal removal was later reversed doesn't appear in the original service letter but is instead included in what appears to be someones retype of the original letter.  Perhaps one of our experts like Reed or Richard can shed some light on this. 

In any event, experience of many owners has been that the 350 engine functions fine without the seals, and removing them eliminates a very definite source of possible damage if they come loose! 
Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: gtrman on December 21, 2014, 06:46:14 PM
Hi fellas, I'd like to re-ignite this discussion on crank seals. I had to shelve my project for a number of years,  but, i'm back at it now.

Does anyone have experience to offer about the omitting of these seals pro or con?

Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: OldSwartout on December 22, 2014, 08:42:53 AM
My  personal opinion on the crank seals is that they are probably not needed for average riding, especially with most rider's typical use these days. If you ride the 350 at high RPM/high throttle for extended lengths of time; i.e., many miles of extended interstate or good open highway riding, the lack of seals might be a problem.  The 350 connecting rods don't have slotted bottom ends like the 175's and many other manufacturers' engines of that size did. I suspect that in factory testing and a few cases of street bikes/racing, that some may have failed or blued the bottom end bearings.

Reed's experience says that most are OK without the seals.

This is strictly speculation on my part, so take it with a grain of salt.

Back in the go-kart days of the 50' & 60's, one of the modifications to get chain saw engine bottom ends to live in the kart racing environment was to slot the rod caps, otherwise the rollers would blue and eventually burn and smear.
Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: slawsonb on December 22, 2014, 10:40:58 AM
The engine I am rebuilding now ran its last 10K+ miles with no seals. Some of this was at high speed, but not racing conditions. It saw 90 mph (indicated) frequently, but never for more than 5 (or so) mins at a time. When I tore it down it did not show any signs of rod big end or main bearing overheating. Just my 2 cents.
Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: ziggy stardust on December 22, 2014, 11:36:07 AM
The 40,000 mile GTR engine I've just stripped and rebuilt had the side seals fitted, they were firmly intact showing no signs of breakage or becoming loose. I've left them in place.

Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: farmerdl on December 22, 2014, 12:47:40 PM
The subject of slots in the big ends of the con rods was mentioned.  If I remember correctly Tony Murphy (after Don Vesco)  raced a GTR back in the early 70s and and one of the egine modifications included slotting the big end on the rods and then honing them just enough after to ensure that they were absolutely true and round.  So those of you on this forum with experience in rebuilding these cranks,  what say you?
Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: Gerrit on December 26, 2014, 06:41:18 AM
I have that article, which appeared in MSQ, and in addition to the slotting and honing Tony Murphy also fitted Yamaha TR2 big-end bearings. No doubt these were better suited to high rpm operation than the standard GTR parts.
Regardless of use (street or racing) and lubrication (pump or petroil), I would definitely prefer slotted big-ends, whether the oil collectors are fitted or not. The big-end is the most critical bearing and can only benefit from the slots. 
Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: farmerdl on December 29, 2014, 09:11:58 AM
Which issue of MSQ has the Tony Muphy article?  It may have been a two part story.

Title: Re: Mag Dynamo Rebuild, crank bearing seals
Post by: Gerrit on December 29, 2014, 12:57:43 PM
The issue with the engine mods was the Autumn 1971 issue; apparently there was also an article dealing with the cycle parts of the bike, but I don't have that and have no idea in which issue of MSQ it appeared- Summer 1971 perhaps?