85/86 cams for an S4 -Mods required, who does it & cost, performance gain?
01-23-2009, 08:26 PM
#31
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I think i get it now. I remember that plug when i was putting the dust caps on the rear of the heads. its clammped between the rear bridge. if you left open, isnt that ok because it would be running against a bearing surface? or is the cam just not long enough or something? so, you have to pull the cam covers and take a hack saw to the cam ends! 
(and put that plug back in )
what about lubrication if you leave the cams length extended ?
mk
(and put that plug back in )what about lubrication if you leave the cams length extended ?
mk
Your guess is correct.
Normally on the S4 heads / cams, these holes would have plugs in them. The idea was to keep the cams long to: 1.) not have the rear most lobe cantelevered and 2.) we thought there is no real harm in having the extra length.
The issue is the one, darn oil hole that does not get covered by a ground bearing diameter journal for the pass side EX. The rear journal of the S3 cam is not long enough to come forward enough to cover the oiling hole.
Sorry for no pictures, but once you are looking at this with actual parts on the bench, it's pretty obvious to see the problem with the rear most dual cam cap removed while resting the pass side S3 EX cam in its bearing saddles.
For Dennis' build, it is VERY unfortunate to have been so focused on the drivers side thrust mod to have missed plugging this small, but important oiling hole. :^(
Having now gone through this mistake... simplest soln is to shorten the cams to match S4's and follow the WSM for which oiling holes get plugged in the heads. Not putting a plug in the one darn oiling hole is a mistake not to be made again.
Normally on the S4 heads / cams, these holes would have plugs in them. The idea was to keep the cams long to: 1.) not have the rear most lobe cantelevered and 2.) we thought there is no real harm in having the extra length.
The issue is the one, darn oil hole that does not get covered by a ground bearing diameter journal for the pass side EX. The rear journal of the S3 cam is not long enough to come forward enough to cover the oiling hole.
Sorry for no pictures, but once you are looking at this with actual parts on the bench, it's pretty obvious to see the problem with the rear most dual cam cap removed while resting the pass side S3 EX cam in its bearing saddles.
For Dennis' build, it is VERY unfortunate to have been so focused on the drivers side thrust mod to have missed plugging this small, but important oiling hole. :^(
Having now gone through this mistake... simplest soln is to shorten the cams to match S4's and follow the WSM for which oiling holes get plugged in the heads. Not putting a plug in the one darn oiling hole is a mistake not to be made again.
01-23-2009, 09:02 PM
#32
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At quick glance it looks like the longer cam will cover all of the oiling holes. However, at the one location (rear, pass. side EX), there is a second hole that is just in front of where the bearing surface on the cam ends. If the bearing surface on the cam where about 2mm longer, the hole would likely be fully covered.
On the oiling front, with the one extra hole on the S4 head plugged, the S3 and S4 heads would oil the longer cams the same. As mentioned earlier in this thread, the drain back hole from the very back of the head should be checked for being open and able to drain the oil from the rear most bearing back to the main cavity of the head.
On the oiling front, with the one extra hole on the S4 head plugged, the S3 and S4 heads would oil the longer cams the same. As mentioned earlier in this thread, the drain back hole from the very back of the head should be checked for being open and able to drain the oil from the rear most bearing back to the main cavity of the head.
01-23-2009, 09:24 PM
#33
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Mark:
See thread linked below. You even posted in this thread. The initial post shows eactly what Jim has been trying to explain....
https://rennlist.com/forums/928-foru...l-stroker.html
See thread linked below. You even posted in this thread. The initial post shows eactly what Jim has been trying to explain....
https://rennlist.com/forums/928-foru...l-stroker.html
Last edited by Bill Ball; 01-24-2009 at 12:24 AM.
01-23-2009, 09:38 PM
#34
Well..John Davis was bopping around Tacoma and stopped in at a local cam place (for one of his other domestic vehicles). As he was chatting with them he asked if they knew anything about Porsche 928 cams. They replied.....absolutely...seems they were doing a lot of work for none other than Phil Threshie..
They are owed some moola from him too..but aside from that, I think we will look into what they can do for us..especially reducing the base circle on stock S4 cams..since those seem to be floating around everywhere...
They are owed some moola from him too..but aside from that, I think we will look into what they can do for us..especially reducing the base circle on stock S4 cams..since those seem to be floating around everywhere...
01-23-2009, 09:53 PM
#35
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I see one oiling area that should be ok with the cam sitting on it. however, i dont see the other area or where the issue would have been.
Geezz, why didnt you guys just do it like i did? chop off the ends and not change anything!
Im tryning to understand how the longer cam in that bearing area , without the plug is an issue.
mk
Geezz, why didnt you guys just do it like i did? chop off the ends and not change anything!
Im tryning to understand how the longer cam in that bearing area , without the plug is an issue.
mk
Mark:
See thread linked below. You even posted in this thread. This initial post shows eactly what Jim has been trying to explain....
https://rennlist.com/forums/928-foru...l-stroker.html
See thread linked below. You even posted in this thread. This initial post shows eactly what Jim has been trying to explain....
https://rennlist.com/forums/928-foru...l-stroker.html
01-23-2009, 10:01 PM
#36
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See the second oil groove just inside bearing surface on cams rear end? Oil feed into it needs to be blocked if cams are not cut. If this is not done oil pressure will espace from it.
01-24-2009, 12:02 AM
#37
Rennlist Member
I see it. I guess i forgot what that plug looked like. was it thick and have two plugs? I see the issue.
so, how would the 85 heads be any different?
looks like pretty easy fix. get out the dremel!
mk
so, how would the 85 heads be any different?
looks like pretty easy fix. get out the dremel!
mk
01-24-2009, 12:26 AM
#38
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01-24-2009, 12:44 AM
#39
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so, how would the 85 heads be any different?
looks like pretty easy fix. get out the dremel!
looks like pretty easy fix. get out the dremel!
In the 85 heads, the rear oil feeds on the passenger side are closer together, the journal is shorter and the cam bearing covers both oil feeds. During the design of the S4 head, they decided to use a cam with a longer end bearing and the span between the feeds was changed on the rear of the passenger side and front of the front driver side S4 exhaust cam. Hence, the mod that is needed to the driver side thrust bearing when you use an S3 cam in an S4 head. Maybe someone knows why they then decided to cut off the rear bearings and plug the vestigal oil feeds. Personally, I don't like the stock oil feed plugs. Seems like a true afterthought. The rubber holders tend to warp with age and the pins can come loose. Also, I understand the holders are currently unavailable and others have had problems getting the correct pins. Also, you could argue that it would be better for the cam ends to be supported rather than have the last lobe cantilevered.
Anyway, in this case the solution does not involve a Dremel!
01-24-2009, 12:53 AM
#40
01-24-2009, 01:27 AM
#41
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So, the head is different. I can sleep now! thanks!
Dremmel? Yes, thats all we use at the Kibort race car shop. we have a sabre saw, but only a wood blade in it now.
seriously, do you have to pull the cams? sounds like that is the only way. what a drag!
mk
Dremmel? Yes, thats all we use at the Kibort race car shop. we have a sabre saw, but only a wood blade in it now.
seriously, do you have to pull the cams? sounds like that is the only way. what a drag!
mk
Mark:
In the 85 heads, the rear oil feeds on the passenger side are closer together, the journal is shorter and the cam bearing covers both oil feeds. During the design of the S4 head, they decided to use a cam with a longer end bearing and the span between the feeds was changed on the rear of the passenger side and front of the front driver side S4 exhaust cam. Hence, the mod that is needed to the driver side thrust bearing when you use an S3 cam in an S4 head. Maybe someone knows why they then decided to cut off the rear bearings and plug the vestigal oil feeds. Personally, I don't like the stock oil feed plugs. Seems like a true afterthought. The rubber holders tend to warp with age and the pins can come loose. Also, I understand the holders are currently unavailable and others have had problems getting the correct pins. Also, you could argue that it would be better for the cam ends to be supported rather than have the last lobe cantilevered.
Anyway, in this case the solution does not involve a Dremel!
In the 85 heads, the rear oil feeds on the passenger side are closer together, the journal is shorter and the cam bearing covers both oil feeds. During the design of the S4 head, they decided to use a cam with a longer end bearing and the span between the feeds was changed on the rear of the passenger side and front of the front driver side S4 exhaust cam. Hence, the mod that is needed to the driver side thrust bearing when you use an S3 cam in an S4 head. Maybe someone knows why they then decided to cut off the rear bearings and plug the vestigal oil feeds. Personally, I don't like the stock oil feed plugs. Seems like a true afterthought. The rubber holders tend to warp with age and the pins can come loose. Also, I understand the holders are currently unavailable and others have had problems getting the correct pins. Also, you could argue that it would be better for the cam ends to be supported rather than have the last lobe cantilevered.
Anyway, in this case the solution does not involve a Dremel!
01-24-2009, 08:08 AM
#42
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Those holes should always be plugged with GTS full metal pins. With early 4v heads there is problem as oil hole diameter is smaller than pins lower end. Its probably easier to take material away from pins than drill larger holes to heads.
01-24-2009, 04:08 PM
#43
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So, the GTS pins do not use the rubber holder?
01-24-2009, 04:25 PM
#44
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Right. If you order with same old part number should get solid GTS versions. Part is totally different but number is exact same IIRR. GTS version is only one which should ever be used as it will not break like all rubber versions do. Despite this, while back I found rubber and GTS pins side by side from '88 S4 engine which had been done by local dealer just one year before. There were other things wrong in it so its not surprising details like those pins were not done right either. For example one GT cam and three S4 cams. We are currently building three 32V engine locally. All three will receive GTS versions. I would refuse to put any '87+ engine together without solids.
We are currently building three 32V engine locally. All three will receive GTS versions. I would refuse to put any '87+ engine together without solids.
01-24-2009, 10:20 PM
#45
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How much does it cost to get a GT exhaust driver side cam? If its only $500 or so, I think the answer would be to get 85 cams, toss the driver side exhaust cam and put in the GT cam. Its the same duration and timing so its basically identical to the 85 cam.
If it costs $1000 for a new single, GT cam, then, its probably better to try and find someone to do the mod. (assuming you can find a decent set of 85 cams for 5-700 bucks.)
mk
If it costs $1000 for a new single, GT cam, then, its probably better to try and find someone to do the mod. (assuming you can find a decent set of 85 cams for 5-700 bucks.)
mk