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Oil Pump Confusion Unit 650cc SOLVED! #699783 06/27/17 10:45 am
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Peter Gee Offline OP
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In pre Unit days it was real simple, now from 63-72 there seem to be a bewildering variety of oil pumps. I have a DU 33XXX series 1966.

My parts book says my pump should be E3878, then in 1968 it's E6928, in 1970 E9421 and so on. Which models will fit my 1966? Can't find E3878 new or second hand for the life of me..the others, yes.

I have unit oil pumps with the "offset" mounting holes..the pre- units were 180 in line. . I have pump plungers (a) Scavenge 0.487/ Feed 0 .374 and another pump (b) scavenge 0.436 /feed 0.374---this seems to be correct for my year 1966 according to the Workshop manual 650's up to 1970 and must be the mysterious E3878?.

What on earth is the other pump for? A T100 Unit as I also had parts for that lying about? It would seem odd to have a bigger scavenge diameter (0.487 vs 0.436) on a smaller engine, or did Triumph get it wrong in the literature and actually (a) is correct for my 650 since it scavenges faster but delivers the same , both feed plungers being 0.374

Don't want to blow up my rebuild, so it helps to know. Am using the factory 63-70 edition of Workshop manual.

Last edited by Peter Gee; 06/27/17 3:48 pm.
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Re: Oil Pump Confusion Unit 650cc [Re: Peter Gee] #699798 06/27/17 1:52 pm
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Originally Posted by Peter Gee

My parts book says my pump should be E3878, then in 1968 it's E6928, in 1970 E9421 and so on. Which models will fit my 1966? Can't find E3878 new or second hand for the life of me..the others, yes.

I have pump plungers (a) Scavenge 0.487/ Feed 0 .374 and another pump (b) scavenge 0.436 /feed 0.374---this seems to be correct for my year 1966 according to the Workshop Manual 650's up to 1970 and must be the mysterious E3878?


650/750

'63 - '66, E3878 (Scavenge 0.437"/ Feed 0.374")

'67 - 'early' '69, E6928 (Scavenge enlarged to 0.487"/ Feed 0.374")

Late '69 - '79, E9421/ 70-9421 (Scavenge 0.487"/ Feed enlarged to 0.406")

'80 ->, 71-7317 'double check-valve' pump (same 0.487"/ 0.406").







Re: Oil Pump Confusion Unit 650cc [Re: Peter Gee] #699808 06/27/17 3:37 pm
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John Healy Online Content
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And they are interchangeable...


Re: Oil Pump Confusion Unit 650cc [Re: John Healy] #699809 06/27/17 3:47 pm
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Peter Gee Offline OP
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Many thanks in that case...... great.....

Re: Oil Pump Confusion Unit 650cc [Re: Peter Gee] #699853 06/27/17 9:13 pm
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DUHC Offline
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Fascinating! Never knew that. A lot of suppliers just say 'oil pump suitable for 350, 500 & 650 unit construction' which aligns with JH's comment.

Re: Oil Pump Confusion Unit 650cc [Re: Peter Gee] #699860 06/27/17 11:01 pm
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fried okra Offline
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Yes, Peter, I gather the oil pumps are interchangeable but gotta believe the latest two valve pump, or using the four valve pump by maybe grinding the timing cover to allow a proper fit, has to be the best way to go.

Not sure the four valve pump will fit the unit 500cc bikes though.

But what do I know.

fried okra

Re: Oil Pump Confusion Unit 650cc [Re: Peter Gee] #699911 06/28/17 12:18 pm
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Any modifications needed to the crankcase to allow for the larger scavenge and feed ports of the later pumps?

Re: Oil Pump Confusion Unit 650cc [Re: Irish Swede] #699957 06/28/17 9:49 pm
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Peter Gee Offline OP
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As far as I know Irish Swede, no, none... enlarging the feed holes would reduce the pressure when the pump plunger was enlarged to increase it......

Re: Oil Pump Confusion Unit 650cc [Re: DUHC] #699958 06/28/17 9:50 pm
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Peter Gee Offline OP
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Yeah like a lot of Britbike things, there is a ton of subtly and I thought the same till I started measuring pump plungers!


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