Drive plate bolts BMC 1.5

[StephenA]

Does anyone know where we can get some new bolts that fix the drive plate into the recess in the flywheel?

 

We seem to have a mix of bolts some are a 7/16 hex head the others are a 3/16 allen head.

[Tracy D'arth]

15 minutes ago, StephenA said:

Does anyone know where we can get some new bolts that fix the drive plate into the recess in the flywheel?

 

We seem to have a mix of bolts some are a 7/16 hex head the others are a 3/16 allen head.

They are 5/16"  UNF set screws. The head is fairly unimportant but normally hex with spring lock washers. Any decent engineers suppliers will have them. They should all be the same type and length as otherwise you will affect the balance a bit.

I don't understand the 7/16" hex head, 5/16" screws should have a 1/2" hex AF head. Has the flywheel been modified in some way?  !/4" screws usually have 7/16" AF heads.

Set screws are threaded to the head, bolts have a section of plain shank.

Edited June 18, 2023 by Tracy D'arth

[StephenA]

9 minutes ago, Tracy D'arth said:

They are 5/16"  UNF set screws. The head is fairly unimportant but normally hex with spring lock washers. Any decent engineers suppliers will have them. They should all be the same type and length as otherwise you will affect the balance a bit.

I don't understand the 7/16" hex head, 5/16" screws should have a 1/2" hex AF head. Has the flywheel been modified in some way?  !/4" screws usually have 7/16" AF heads.

Set screws are threaded to the head, bolts have a section of plain shank.

 

All we know is that one of the bolts isn't an allen head -its a traditional head for a spanner and seemed to be a 7/16th spanner fit. There also seemed to only be 4.

[Slim]

As said previously  5/16" UNF. On my 1.8 I used cap screws as they were much easier to tighten (access and clearance)

Without doubt use new spring washers. A dab of thread sealer wouldn’t go amiss.

Make sure you find any missing bolts. Mine came loose after thousands of hours, got picked up somehow by the flywheel/ring gear and basically blasted their way through the aluminium Bell housing. An expensive mid cruise repair and an eventual replacement. Any remaining bolts debris looked like ball bearings

Edited June 18, 2023 by Slim

[Tracy D'arth]

9 minutes ago, StephenA said:

 

All we know is that one of the bolts isn't an allen head -its a traditional head for a spanner and seemed to be a 7/16th spanner fit. There also seemed to only be 4.

I don't understand "only 4" there are 6 in the flywheel normally. Is there a weight pad bolted to the flywheel? Or an adapter of some type? A picture would be a good idea!

[StephenA]

There were only 4 bolts holding the spring plate into the recess in the fly wheel - three allen headed ones and a regular one. We only found this out when we lost drive and having confirmed that the gear box was OK as far a we could tell we dropped the gearbox and the end plate off the bell housing and the enitre spring plate came out with the gear box and the screws were lying in the bottom of the bell housing. No photos of the spring plate / flywheel unless we head back to the boat and take it all apart again.

[MtB]

2 minutes ago, StephenA said:

There were only 4 bolts holding the spring plate into the recess in the fly wheel - three allen headed ones and a regular one.

 

Just to clarify, are you saying there are six holes but only four bolts in them, i.e. you found there were two bolts missing when you took it to bits?

 

Or does your flywheel and drive plate have only 4 holes and 4 bolts?

[StephenA]

6 holes I think - suspect the drive plate has more.

[Tracy D'arth]

Multi fit drive plates can have lots of holes.

 

Am I to understand that you have just put it all back together with just 4 bolts?

[StephenA]

Just now, Tracy D'arth said:

Multi fit drive plates can have lots of holes.

 

Am I to understand that you have just put it all back together with just 4 bolts?

 

As that was all we had and we broke down in the middle of nowhere we put it back together with the 4 bolts (and no spring washers)  that have been all that's holding it in place for I have no idea how long. Now we are back on the mooring we want to get it fixed properly

[Tracy D'arth]

11 minutes ago, StephenA said:

 

As that was all we had and we broke down in the middle of nowhere we put it back together with the 4 bolts (and no spring washers)  that have been all that's holding it in place for I have no idea how long. Now we are back on the mooring we want to get it fixed properly

Good man, best to do it properly 'cos it will fail again with only 4 screws. Not good for the flywheel teeth chewing steel.

The set screws need to be high tensile, allen cap heads are.  Grade 8.8 or better 10.9 hex set screws will do.  Do check on the size though, 5/16"  is normal, about as thick as a disposable ball point pen.

[john.k]

Interesting factoid............since Unbrako has migrated to India .....the quality of the fasteners has taken a massive dive and what used to be very high tensile grade is now at best gr 8.8 ,and that doubtful.

[adrianh]

Also beware of the very light duty spring washers now sold that wind open under a cap screw head. Better to use 5/16 x 1inch long ( i think) 8.8 or 10.9 grade setscrews and the heavy duty flatter appearance spring washers if you can find them.

I have seen suppliers of fixings for old classic cars that still list proper old stock fixings, google ford and other american car parts as they used unf still when others had gone metric.

Check your local ford spares garage.

UNF screws are marked with 3 ' spoke type ' lines or a series of small circles on the head or a recess in the middle of the head and generally are 1/2 af hexagon .

If all else fails try a car breakers yard!

 

[BEngo]

Namrick are good for small numbers of old style fastenings in HT and mild steel.

Not cheap though.

 

Not sure about marine drive plate fastenings, but IIRC the road  B series clutch pressure plate was held to the flywheel with special bolts with a short plain portion to take the load from the plate.

 

N

[Tracy D'arth]

Loads on ebay.

https://www.ebay.co.uk/itm/371103141655?

[Tony Brooks]

25 minutes ago, BEngo said:

Not sure about marine drive plate fastenings, but IIRC the road  B series clutch pressure plate was held to the flywheel with special bolts with a short plain portion to take the load from the plate.

 

I am sure that they also had a pair or three dowl pins as well, but can't recall seeing any use for marine drive plates.

[Tracy D'arth]

3 minutes ago, Tony Brooks said:

 

I am sure that they also had a pair or three dowl pins as well, but can't recall seeing any use for marine drive plates.

The dowel pins have to be removed usually to fit the drive plate unles R&D have drilled the extra 2 holes in the plate.

[Rincewind]

Whichever type of bolt/setscrew you decide on, to prevent the screws coming loose when the engine is running drill a small hole through each of the heads and once they are secured, wire them together in pairs.  You can use galvanized wire obtained from armoured electrical cable with a drill size slightly larger and yes, "allen" type screw heads can be easily drilled if you ensure your drill bit is sharp.  The wire will not affect the balance.

[john.k]

May be able to get automotive type flange head bolts with serrated locking underside .........most cars use these exclusively now ,no washers needed.

[Mikexx]

3 hours ago, Rincewind said:

Whichever type of bolt/setscrew you decide on, to prevent the screws coming loose when the engine is running drill a small hole through each of the heads and once they are secured, wire them together in pairs.  You can use galvanized wire obtained from armoured electrical cable with a drill size slightly larger and yes, "allen" type screw heads can be easily drilled if you ensure your drill bit is sharp.  The wire will not affect the balance.

 

My go-to in these situations is to use threadlock. It stops bolts coming loose as well as keeping them captive.

[Tracy D'arth]

53 minutes ago, john.k said:

May be able to get automotive type flange head bolts with serrated locking underside .........most cars use these exclusively now ,no washers needed.

Are these bolts high tensile? Very good to use but they seem to be used mainly on auto bodywork rather than heavier auto engineering.

[BEngo]

4 hours ago, Rincewind said:

Whichever type of bolt/setscrew you decide on, to prevent the screws coming loose when the engine is running drill a small hole through each of the heads and once they are secured, wire them together in pairs.  You can use galvanized wire obtained from armoured electrical cable with a drill size slightly larger and yes, "allen" type screw heads can be easily drilled if you ensure your drill bit is sharp.  The wire will not affect the balance.

Proper stainless steel locking wire is available on Amazon for not too much money.  

 

Frost Auto Restoration sell a widget for drilling lock wire holes.

 

If wire locking take great care to

 

A: get the locking wire in a tight Z not an S (on right hand bolts).

B: Bend the loose end last 3mm over so it doesn't rip chunks out of your hand.

 

N

[Tracy D'arth]

Very old aircraft practice using wire locking, I have not done this for many years. 

 

Used to be standard practice on all airframes and engines, I still have the special wire pliers somewhere.

BMC didn't bother and clutch assemblies did not fall off. A touch of Loctite will do if you feel it necessary.

[Tony Brooks]

If I was worried enough to use lock wire I think that I would knock up some lock tabs

[Tracy D'arth]

7 minutes ago, Tony Brooks said:

If I was worried enough to use lock wire I think that I would knock up some lock tabs

There is not much to lock the tabs against on a drive plate  though; unless you take them over the edge of the flywheel,  which would not be very good. Between 2 bolts would be a stretch.