103 replies to this topic

[73TORANA!]

I would be interested in what they have to say.

[claysummers]

All they said was, better if they rebuild my Bosch one, as long as the module is good. Price dependant on its condition and how much they need to do to it, but up to $450. There is no saving doing it this way if it costs that much, but I end up with a better result. From that I assume they use a Chinese module, I’m not sure. I’m going to post one off to them soon.


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[73TORANA!]

Thanks mate,

The only time I have heard of a Bosch module failing is if the white thermal conductive paste dries out and the module cant transfer it heat to the dizzy body. You can get the thermal paste from Jaycar and it will last over 5 years.

I Think you can still get new Bosch modules but if yours was working it should be fine and they will put new paste on it.

If you have any spare HEI dizzies in the shed I would replace the thermal compound anyway just as a precaution as its an age thing. 

[claysummers]

Thanks Geoff. Yes, I replaced the thermal paste in one I tried recently. I did shim this one up as it had something like 0.10” float, but I probably left still too much play in it. In any case it didn’t perform well in use, pinging or pinking all over the rev range. Time to bite the bullet and fork out.


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[EunUCh]

Interesting read , the curves pictured are from a hk shop manual , obviously for std. comp. engines but it might be helpful to help us see what's going on .

 dist timing.jpg   306.09K   4 downloads

[73TORANA!]

When you send it out ask them if they can provide a graph of your curve. I should have done that when mine was done as its good to have reference data in case you change something.

[claysummers]

Good idea. One of the techs is supposed to phone me to discuss when they have assessed it.


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[S pack]

I spoke to a GMH engineer back in the 80s about why they used the shitty plastic gear for the dissy in the 6-cyl & he explained then about spark scatter, there must be something to it.

 

I've fitted the metal oil pump gear to many Holden 6-cyl dissies & while I never had any dramas on street cars I did have a few on higher revving engines.

 

Dr Terry

A Feb 1972 Dealer Service Letter regarding a trial of nylon distributor drive gears on 253 and 308 v8 engines.

 Nylon drive gear DSL.jpg   165.76K   8 downloads

[73TORANA!]

Interesting service letter thx for posting.

[Bruiser]

I think I read somewhere someone quoting a 15 year service life for nylon gears (?)

Hey

Wasn’t it kind of gmh to make the oil pump shaft the same exact size as the dizzy shaft
so the gears can be swapped around
Just to give us a saucy mystery to solve all these years later

Maybe try putting the nylon gear from the dizz on the oil pump
and see how that goes

[claysummers]

So maybe scorcher or Performance ignition Systems to be correct, will replace mine. I sent them the complete unit with cap and rotor. Now the rotors are obsolete they are not cheap.


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[73TORANA!]

Yeah they replaced mine, they did give the old one back but do you think I can find it.

Hahaha plastic oil pump gear.Thats gold

[EunUCh]

Nothing wrong with metal gear on dizzy , just set end float on dizzy to about 3 thou. Then go from there. The plastic ones tend to expand then split and end up in sump.

[S pack]

I think I read somewhere someone quoting a 15 year service life for nylon gears (?)

Hey

Wasn’t it kind of gmh to make the oil pump shaft the same exact size as the dizzy shaft
so the gears can be swapped around
Just to give us a saucy mystery to solve all these years later

Maybe try putting the nylon gear from the dizz on the oil pump
and see how that goes

Never use the nylon drive gear on an oil pump.

[Bruiser]

Thanks Dave
I shouldn’t be a goon about something so guaranteed to
Destroy your engine
In case someone misses the joke

[claysummers]

Finally got the distributor back.



It is set up to put 22 degrees in by 4000 rpm, and they put a steel gear on it.

The funny thing is the car has been pinging (or pinking) 2000 to 2600 rpm the last two tanks, 95, then 98. Now it has stopped 1/2 way through the second tank.

[yel327]

I do find that in the Ram Clay. Sometimes fuel must be cr@ppy. Will ping on 98 then be fine. Then fine on E10, then ping a week later. Shame there isn’t a fuel quality sensor on every car.

[claysummers]

The ideal would be computer controlled with a knock sensor, which surely the Ram has Byron?


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[yel327]

They do, but it'll still ping before it detects it. I thought it was the timing adjusting too, but I think it is just fuel variations that cause it initially.

[claysummers]

Installed at 12 degrees initial. The light shows the timing rock steady at idle. The other three dissys all tended to jump around to varying degrees. Only tested up to 3k but seems good, so far.


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[73TORANA!]

Was your timing steady a 3k

[claysummers]

Was your timing steady a 3k

So far I only road tested Geoff. They did fit a new steel gear.


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[73TORANA!]

I wonder if your pinging is carbon build up??

[claysummers]

Yes, me too. That is why I have been putting upper cylinder cleaner through when it occurs. I wonder if the 0.070” squish height contributes to carbon build up. AsByron says it does seem o happen to everyone. My mate is using racing fuel and still pinging.


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[73TORANA!]

On mine the squish is what ever a standard gasket is. the block was decked 10thou with the pistons left at the height they came at so im guessing it prob about the same as yours?. Could you have a lean mix at the 2k to 2.6k point? 

 

On a side note ive been doing a lot of research on combustion chamber squish and the general consensus, is far as timing goes, seems to be that as swirl and turbulent airflow in the cylinder speeds up when up on the cam at higher rpm that this all helps the flame front to propagate across the entire cylinder more efficiently to a point that timing advance above a certain point is no longer needed, more or less.

So this would explain the all in by 4k rpm theory i guess, im sure there are other considerations to take into account.