PodOne Posted December 11, 2020 Report Share Posted December 11, 2020 Hi all As ever a few questions. Just got a new Kent PI cam shaft to replace the old one as the lobes were worn. On measuring the new and old bearing surfaces they are the same so no wear. However both cams seem to have play once inserted into the block. Is it normal for the block bearing surfaces to wear rather than the cam? There appears to be around 2.8 thou of play. Probably explains why the previous owner had added another spring to the pressure relief valve in an effort to boost the oil pressure. Would wear here lead to low oil pressure? The plan is to have the block line bored and shells fitted. 1) who supplies/make are the best bearings shells? 2) what''s the best clearances to aim for? Only because I've read that the OEM specs can some times lead to the cam seizing up. Thanks Andy Quote Link to post Share on other sites
Tom Fremont Posted December 11, 2020 Report Share Posted December 11, 2020 Hi Andy, If the clearance you cite is diametral it means ~ 0.0014" gap all round. Not too much, necessarily as the fit isn't so snug as to give any resistance to insertion. Shells are fine if you get the machinist to do it well; he may find the bores are not parallel with those of the crank and can fix that if so. There will be resistance with shells; this because the joint isn't perfectly round so will give a high spot there. Won't ever seize; that's the good news. Some may not be aware of the role the oil grooves play in oil pressure; one of my engines with fresh shells and new cam gained 30+ psi from one cam to the next; grooves were very large and quite fine respectively. Note the valve springs press the camshaft into the oil feed holes of the block bores. If the bores are (1) round and (2) equal they should be OK. Tom Quote Link to post Share on other sites
TriumphV8 Posted December 14, 2020 Report Share Posted December 14, 2020 Hi, the shells are from Spitfire 1500, who used them for a limited time. Clearance ist 0,03mm or a bit more. I did the drilling by myself in an old milling machine and found it necessary to drill all bores in one step and have a support at the clutch side. Quote Link to post Share on other sites
JohnC Posted December 20, 2020 Report Share Posted December 20, 2020 On 12/12/2020 at 8:31 AM, Tom Fremont said: one of my engines with fresh shells and new cam gained 30+ psi from one cam to the next Hi Tom, Thanks for the info - you've solved a puzzle for me. I recently replaced my cam and the oil pressure at idle (fully-warmed engine) dropped by 15-20psi. Looking at a photo of the new cam I can see that the one oil groove I can see is much wider than those on the cam I removed. I've been troubled by how low the pressure now is (~15psi @ idle), to the point of considering an engine out & camshaft bearing mod. I have already replaced all main & conrod bearing shells (none were worn). I may instead have a hunt around for an original CP cam or an aftermarket one with narrow grooves. The one I fitted is a CP profile but not original. Swapping the cam is a pain but a lot less work than having cam bearings installed! Cheers, John Quote Link to post Share on other sites
Tom Fremont Posted December 21, 2020 Report Share Posted December 21, 2020 Hi John, The low oil pressure culprit camshaft only had 150 miles on it when I took it out. Hating the task of removing (3) Webers, manifolds, head etc. I managed to extract the cam, followers and insert their replacements with the head on. I got some hints from various folks here and using a sheet of aluminium formed a trough, suspended the followers with Bo- Peep hooks and dropped them into it, withdrew them and stood up new ones, suspended them likewise and slid the new cam into place. Saved a ton of work! These were the implements: Cheers. Tom Quote Link to post Share on other sites
Tom Fremont Posted December 21, 2020 Report Share Posted December 21, 2020 On 12/19/2020 at 10:14 PM, JohnC said: Hi Tom, Thanks for the info - you've solved a puzzle for me. I recently replaced my cam and the oil pressure at idle (fully-warmed engine) dropped by 15-20psi. Looking at a photo of the new cam I can see that the one oil groove I can see is much wider than those on the cam I removed. I've been troubled by how low the pressure now is (~15psi @ idle), to the point of considering an engine out & camshaft bearing mod. I have already replaced all main & conrod bearing shells (none were worn). I may instead have a hunt around for an original CP cam or an aftermarket one with narrow grooves. The one I fitted is a CP profile but not original. Swapping the cam is a pain but a lot less work than having cam bearings installed! Cheers, John Piper made both the oversize groove cam and the diminutive groove replacement for me. And see post above for installation tips . Tom Quote Link to post Share on other sites
PodOne Posted December 21, 2020 Author Report Share Posted December 21, 2020 Thanks all for the feedback, much appreciated. After communication with the machine shop who have better measuring kit and Chris Whitor the cam housings although round are out of spec so will be line bored and Spitfire 1500 shells supplied by Chris installed. Interesting read regarding the difference the groove in the cam shaft makes to oil pressure. The new cam came from Kent Cams via Chris and ground from a new blank so I hope the oil groove is as OEM as its now with the machine shop so I can't check. Saying that if Chris is selling them I suspect it will be fine. Andy Quote Link to post Share on other sites
JohnC Posted December 21, 2020 Report Share Posted December 21, 2020 3 hours ago, Tom Fremont said: suspended the followers with Bo- Peep hooks How did you do that bit? I can't see anything to grab onto when the cam followers are down in their guides. I thought about a piece of dowel with an interference fit into the follower, but that only needs one to slip and I have to go grovelling around for a follower in the sump! John Quote Link to post Share on other sites
Tom Fremont Posted December 22, 2020 Report Share Posted December 22, 2020 15 hours ago, JohnC said: How did you do that bit? I can't see anything to grab onto when the cam followers are down in their guides. I thought about a piece of dowel with an interference fit into the follower, but that only needs one to slip and I have to go grovelling around for a follower in the sump! John John, The " Bo-Peep " hooks are more than tight enough in the follower bores to hold them, clothespins then holding them up. An oversize corkscrew shape could do it even better but a simple hook worked for me. A straight wire is used to push them off, both the old ( into the trough ) and the new ( onto the new camshaft ). Tom Quote Link to post Share on other sites
Lebro Posted December 22, 2020 Report Share Posted December 22, 2020 Very inventive, not sure I would have considered that as feasable, well done. Bob. Quote Link to post Share on other sites
JohnC Posted December 22, 2020 Report Share Posted December 22, 2020 8 hours ago, Tom Fremont said: The " Bo-Peep " hooks are more than tight enough in the follower bores to hold them, clothespins then holding them up. An oversize corkscrew shape could do it even better but a simple hook worked for me. A straight wire is used to push them off, both the old ( into the trough ) and the new ( onto the new camshaft ). Love your work. I'll let you know how I get on, if I decide to try a new cam. I fear the bearings are probably shot though, as this all started when my oil cooler sprung a leak. I noticed a small drop in oil pressure after replacing the cooler and am still on its trail. Happily, all main & big end bearings were fine. Perhaps the cam suffers from oil starvation first. Or maybe my oil pressure sender is shot (I can dream)! John Quote Link to post Share on other sites
John L Posted December 23, 2020 Report Share Posted December 23, 2020 I presume you put in the new followers with the sump off? I didnt think they would come up thru the slots in the cylinder head, could you confirm please. John Quote Link to post Share on other sites
TriumphV8 Posted December 23, 2020 Report Share Posted December 23, 2020 Back to the cam bearings: Here are some photos of my work. Bearings are from CuSn12 puller made to bring them absolutely straight into the block with proper position of oil holes and last picture with cam in the block ready to use Quote Link to post Share on other sites
Tom Fremont Posted December 23, 2020 Report Share Posted December 23, 2020 8 hours ago, John L said: I presume you put in the new followers with the sump off? Yes. After the cam and old followers are removed the new ones are inserted into the trough one by one and using a straight wire from above and a gentle nudge from behind they are stood up to vertical so the hook can be pushed into the bore, then carefully lifted into the block bore and suspended with a clothespin. Once all (12) are in the cam is inserted, lobes greased and the followers are all pushed off their hooks onto the cam. I only did this because the defective cam had only 150 miles on it and all else was as new. Tom Quote Link to post Share on other sites
canbrake Posted December 24, 2020 Report Share Posted December 24, 2020 It has been a useful platform, I wish everyone to help each other. Quote Link to post Share on other sites
JohnC Posted December 24, 2020 Report Share Posted December 24, 2020 18 hours ago, Tom Fremont said: After the cam and old followers are removed the new ones are inserted into the trough one by one and using a straight wire from above and a gentle nudge from behind they are stood up to vertical so the hook can be pushed into the bore, then carefully lifted into the block bore and suspended with a clothespin. Where do you position the trough? I'd assumed it went through the camshaft bearings but then you wouldn't need to remove the sump. Or would you? John Quote Link to post Share on other sites
Tom Fremont Posted December 24, 2020 Report Share Posted December 24, 2020 8 hours ago, JohnC said: Where do you position the trough? I'd assumed it went through the camshaft bearings but then you wouldn't need to remove the sump. Or would you? John No need to remove the sump - the trough in the block's cam bores catches the followers. Tom Quote Link to post Share on other sites
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