Any Perkins Diesel Experts?

[EddiePetty]

I am in the process of re-building a Perkins 4 99 diesel and have encountered an odd problem.

I can not keep the cam and injector pump in time with the crank.

The crank gear has 24 teeth, the cam and pump gears have 48 teeth but the idler between the cam and pump has 57 teeth !! This can't right as that is a 2.375 to 1 ratio.

I received the engine in boxes, however the gears came as a new set (5 years ago!!)

I've consulted every Perkins resource I can find but cannot find any information on gear tooth counts.

(It is my belief that the 4 99, 4107 and 4108 were basically the same engine.)

Any of y'all have any good part numbers and/or contacts for the correct idler gear?

 

[Howard Sterndrive]

Re: Any Perkins Diesel Experts?

the ratio is 2:1

it doesn't matter how many teeth the idler gear has.

If the 48T gear turns once, the 24T gear turned twice.

think about it

found a manual:
http://pdfcast.org/pdf/perkins-diesel-4-108-4-107-and-4-99-workshop-manual

 

[Don S]

Re: Any Perkins Diesel Experts?

the ratio is 2:1

it doesn't matter how many teeth the idler gear has.

If the 48T gear turns once, the 24T gear turned twice.

think about it

^^^^^^^^^^^^^^^^^ What He said ^^^^^^^^^^^^^^

It doesn't matter one bit what the idler does, but the crankshaft must turn 2 complete revolutions while the cam turns one. And it has to happen every time, exactly the same or the timing will be moving every revolution of the crank.

 

[skyking897]

Re: Any Perkins Diesel Experts?

I'm no engine expert but wouldn't the idler gear have to have the same number teeth as either the crank gear or the cam gear in order to maintain the 2:1 ratio. I'm thinking it should be the same as one of them. It seems like simple math. If it wasn't it would not end up as a 2:1 ratio between the cam and crank. I've opened up the accessory case on a Lycoming aircraft engine, now your really talking about gears (crank,idlers,fuel pump,magnetos,cam). All are the same tooth count except the cam gear which is double the tooth count as the others. Again, it seems like simple math to me unless I'm missing something here.

On edit: The only thing the idler gear does is change the rotation direction of the driven gear, so it has to be the same number of teeth.

 

[Howard Sterndrive]

Re: Any Perkins Diesel Experts?

I'm no engine expert but wouldn't the idler gear have to have the same number teeth as either the crank gear or the cam gear in order to maintain the 2:1 ratio.

no, it has no effect

The idler can have 10 teeth, or 13,452 teeth

The overall ratio of driving and driven will not be affected.

 

[redjmp]

Re: Any Perkins Diesel Experts?

Idler gears dont turn anything except the driven gear and so they pass on the rotation on a tooth by tooth basis. The idler gear in your case is turning some stange ratio but it matters not as only the ratio of the driven gear counts.
Think about. That idler could have 20 or 60 teeth and if it was 20, it would turn 3 times faster, but the driven gear wont turn any faster.
Usually, all an idler gear is used for is reversing direction and has no effect on the gear ratio.

 

[vxtech]

Re: Any Perkins Diesel Experts?

i have a pdf file with tooth count specs, some engines were spur gear and others were helical gear with different tooth counts, just don't know how to post file to thread,i can email it to you

 

[EddiePetty]

Re: Any Perkins Diesel Experts?

vxtech,

Check your Private Messages...Ed

 

[EddiePetty]

Re: Any Perkins Diesel Experts?

Don, Howard & Red...

Just like the XO tells me: Sometimes the obvious escapes me!!!

Y'all are exactly right and I should have known better. Guess I've just been in front of this Perkins too long. I aligned all the marks again today, rotated 720 degrees and of course the marks on the idler were in left field but the marks on the other three gears were right where they were supposed to be!!!
Dummy me...I thought with age comes knowledge. I must have missed that boat.
Thanks for the awakening, Ed :redface:

Oh, and Howard....Thank You for the PDF !!!