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E: Engine Half Time Pinion Sizes

LoneStar

Well Known and Active Website User
VOC Member
Hello all,

My current ET49 half time pinion, combined with new cam gears, has backlash in its engagement with the idler gear. I know these pinions are available in various sizes to deal with this situation - but I'm not clear on what exactly "+.004" means, for instance.

Is there any way to determine which size is likely to be needed, based on some measure of the existing backlash?

Thanks,

Dave
 

Robert Watson

Well Known and Active Website User
VOC Member
+.004 means that the gear is .004 bigger than standard for the gear. You measures gears by fitting specially ground pins between the teeth and measuring across the gear to give a dimension. If you do this then you can look up what standard is and then pick a slightly bigger one to try.

it means either a wait while suppliers ship gears back and forth, or finding someone in your neighbourhood who has a bucket full of them in stock!
 

LoneStar

Well Known and Active Website User
VOC Member
Robert,

Thanks. My current, too-small, pinion is stamped +4. The requirement is to eliminate backlash, and the challenge would be to translate a diameter increase into backlash reduction. Someone much better at geometry than me could probably do it, and determine the gear oversize that would fit perfectly.

As it stands, Coventry Spares has three oversizes beyond .004, and a friendly return policy - so I expect I'll order all three and send back two.
 

BigEd

Well Known and Active Website User
VOC Member
VOC Forum Moderator
Robert,

Thanks. My current, too-small, pinion is stamped +4. ............ Someone much better at geometry than me could probably do it, and determine the gear oversize that would fit perfectly. ........

As it stands, Coventry Spares has three oversizes beyond .004, and a friendly return policy - so I expect I'll order all three and send back two.
Take advantage of Coventry Spares return policy and save yourself a lot of time. If you think you might like to try measuring then there are a series of articles in WhitakerPedia (link below) written by Neville Higgins, "The Prof" and then think on. :)
Measuring timing pinions
 

Marcus Bowden

Well Known and Active Website User
VOC Member
Our Ki Wi friends down under have a spares system where they keep a full set of HT pinions and send the set, then the owner will select the correct one he needs and send the rest back with spares holder ordering a replacement. I'm sure we could do this at the VOCSC.
 

John Cone

Well Known and Active Website User
VOC Member
When i rebuilt my engine, Maughans sent me a box with all the various size half pinions in. You select the one you need and send them back and pay for it.
 

Cyborg

Well Known and Active Website User
VOC Member
Having a selection of gears to choose from definitely makes life way easier. The plus .004 may no longer be plus .004 due to wear. It’s possible it never was plus .004 depending on who made it. When setting backlash, watch for cam pinions, large idler etc. being out of round or bushings that are not quite centralized.
You might find using thread wire gauges to measure the gears is a bit awkward if you’re not used to doing it. I haven’t spent a lot of time measuring them so when there is a discrepancy between the stamped size and the micrometer, I still wonder if it’s the gear or me.
You mention new cam gears, so hopefully they are round. If you pressed them on the cams yourself, then best to make sure the outboard cam bushings have sufficient clearance on the spindles.
 
Last edited:

LoneStar

Well Known and Active Website User
VOC Member
Thanks everyone. It seems there's quite a lot of information out there, and that measuring these gears isn't particularly simple (although the spindle-distance approach provided by VOCS is workable). Given the ease of ordering several sizes and keeping the best fit, that seems the best approach.

My cam gears are from Maughan, installed by Megacycle who also sized the bushes to new spindles. The idler is steel, some years old but likely from Maughan. So, reason to hope for a trouble-free setup.

I do have to clean up the mainshaft threads, as they're distorted due to the unfortunate practice of punch-locking the nut.
 

Bill Thomas

Well Known and Active Website User
VOC Member
We have had this before, Megacycle have fitted bronze bushes instead of our oilite type,
And they need more clearance ??. Cheers Bill.
 

Cyborg

Well Known and Active Website User
VOC Member
Yes... not a big fan of punch locking. Much prefer Loctite. Some types of Loctite apparently aren’t bothered by a bit of oil on the threads, but I prefer to make sure they are squeaky clean. Similar to cylinder bores after honing... when you are sure they are absolutely clean, you’re almost done. Seems to me that the small nuts on the valve lifter pivots were punch locked originally. Seems brutal to me, but not sure what was available back then. Loctite appeared in 56 I think.
Someone here will probably ask what bushes you had installed in the cams. Coming from Maughan, I assume they are oilite.
Edit... someone asked while I was writing this.
 

Cyborg

Well Known and Active Website User
VOC Member
We have had this before, Megacycle have fitted bronze bushes instead of our oilite type,
And they need more clearance ??. Cheers Bill.
Bill, you and I are enter highjack territory again. Is it a question of them needing more clearance or is it a case of folks getting cams from Megacycle and installing their own pinions and not resizing the bushing back to the proper clearance? I have no idea.
Now we can debate the best method for resizing the bushings.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Sorry, I will have to have a holiday,
I don't think it will be too bad to have a bit of slack H/T/P., The noise comes from the other pinions if too tight.
It depends how slack ?, I think they only go up to plus 10 ?.
 

LoneStar

Well Known and Active Website User
VOC Member
The cams and bushings were supplied by Megacycle - I sent them the new gears and spindles for fitting. They did install bronze bushings; hopefully they set the clearance to something appropriate for the material.

Questions,

- Why is Oilite preferred over bronze for cam bushes, given that the area is oil-drenched?
- What calamity is likely with bronze bushes?
 

Cyborg

Well Known and Active Website User
VOC Member
I’m really not the person to answer those questions. Oilite if I understand completely, has pores filled with lubricant , so they will presumably tolerate interruptions of..or low oil supply better than bearing bronze. Again, I don’t know for sure, but you may be over optimistic when you say oil drenched. I haven’t had any personal experience with Megacycle’s bushings, but understand from comments on the forum that folks have had then seize on the spindles. Whether that is directly related to the bushing material or simply a lack of clearance for oil to get into the bushing in sufficient quantity because the bushings were’t opened back up again after the pinion was pressed on remains a question I have. Just wanted to make sure you were aware of the debate.
 

Bill Thomas

Well Known and Active Website User
VOC Member
I’m really not the person to answer those questions. Oilite if I understand completely, has pores filled with lubricant , so they will presumably tolerate interruptions of..or low oil supply better than bearing bronze. Again, I don’t know for sure, but you may be over optimistic when you say oil drenched. I haven’t had any personal experience with Megacycle’s bushings, but understand from comments on the forum that folks have had then seize on the spindles. Whether that is directly related to the bushing material or simply a lack of clearance for oil to get into the bushing in sufficient quantity because the bushings were’t opened back up again after the pinion was pressed on remains a question I have. Just wanted to make sure you were aware of the debate.
We have been told, The same can happen in gear boxes, When the wrong bushes have been fitted.
 

rogerphilip

Active Website User
Non-VOC Member
Hello all,

My current ET49 half time pinion, combined with new cam gears, has backlash in its engagement with the idler gear. I know these pinions are available in various sizes to deal with this situation - but I'm not clear on what exactly "+.004" means, for instance.

Is there any way to determine which size is likely to be needed, based on some measure of the existing backlash?

Thanks,

Dave
Hi Dave
Just a thought, but I have in the distant past measured / checked differences in gear sizes by measuring over drills placed in the gaps using three for odd teeth and four for evens.
I have also used this method to measure a male thread on an otherwise scrap component, thus enabling me to replicate the thread on a replacement component with a reasonable degree of accuracy, without the luxury of modern form tools, a gauge, or the matching female component.
HTHs
Regards
Roger
 

davidd

Well Known and Active Website User
VOC Member
- Why is Oilite preferred over bronze for cam bushes, given that the area is oil-drenched?
- What calamity is likely with bronze bushes?
Having talked with Megacycle a month ago, they will now supply Oilite bushings, but I think you have to ask. Phosphor bronze is just too quick to pick up metal. The oil supply to the cams is just not steady enough. Using phosphor bronze has cost a few owners thousand of dollars and many hours of time, so the risk/reward calculation is really skewed. Those owners that have made this mistake have had bent valves, damaged pistons and damaged followers. The Oilite bushes are a few dollars.

David
 

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