Cylinder head

[rgh0]

And chatting to Peter, above, this afternoon, his engine people say they will not put in bronze guides in a twink head, unless you want them replaced again, in very short order.

No, I will take a lot of convincing on the bronze guide debate, I will stick with original.

Leslie

I dont understand the concern about using bronze guides in a Twink -- can Peter's engine people explain more?

The original iron guides were used based on cost rather than superior long term performance and wear was always an issue due to their short length and the relatively poor wear performance of iron. Modern bronze guide alloys generally will perform substantially better than iron in all aspects. In a low mileage road car with modern oils though use of either will probably not be a problem these days IMHO. In a more highly stressed race engine use of bronze guides is a must especially for cooling on the exhaust valve. If i was building a road engine intended for high mileage daily use i would also use Bronze guides. In fact around here its hard to get the iron guides as everyone one only stocks bronze ones.

cheers
Rohan

[512BB]

Interesting Rohan. From what I remember Peter telling me, he said that they had fitted bronze guides to other folks heads, not his, and that they had seen the heads back again, AFTER A PERIOD OF TIME, with those guides worn.

Of course, we do not know what use those heads had been put to, during that time, or what the period of time was, but there you are. They said that they would fit bronze to his head if he wanted them to, but they did not recommend it. If I have got any of that wrong Peter, please come back and correct me, or add anything that I have missed.

rgh0 wrote: The original iron guides were used based on cost rather than superior long term performance and wear was always an issue due to their short length and the relatively poor wear performance of iron.

You, like me, have a few heads kicking about the place. Now I have not examined all of them for wear in the valve / guide department, but certainly, one that I looked at recently, that I believe came from a 100k mile car, did not display what I would call excessive wear in that area.

Of course, what you have to remember is, very few of us will have actually had a twin cam engine from new, or used a twink for 100k miles after a proper rebuild. In all instances, I am talking about road use, not race applications. Therefore, we do not know how well, or not, the engine has been maintained over that period, and that is the key to longevity with these engines, quality maintenance by competant fiddlers.

We have all been to view the car for sale, that on pulling out the dip stick, reveals a thick black filthy mess that hardly has the capacity to drip off. And that is my point. Most twinks were run like that in the old days, and therefore, is it fair to judge the wear characteristics of the guides, when in all probability, we do not know the history of the engines maintainence?

Our cosseted cars today, more than likely, receive far more oil changes than even the schedule recommends, and as the saying goes, 'the oil is the lifeblood of your engine', fail to change on fear of death, of your engine.

So, as you say, for a road car, I feel that the original part, is more than adequate for the application, provided the engine is maintained to good standards. Lets face it, how long will it take most folk to cover 50k miles, and after which time, the engine is due a rebuild anyway. Although many will go on for 1000's of miles more with no issues, if they have been well looked after.

Leslie

[avro]

Hi All


I thought that Rohan as usual has got it right and there is little that I could add to his comments on the advantages of bronze guides

As someone who has been known to dabble with more than the odd Twincam engine over the last 30 plus years I would have to say that I haven't fitted a set of iron guides for at least 20 years. Yes the bronze guides are a little more expensive than iron guides and they can be a little more difficult to size, especially the colsibro bronze guides. These are considered to be the very best material available but can be difficult to ream, however with guide honing equipment a full set can be sized within a few minutes.
I'm suprised to hear that any experienced machine shop would find bronze guides an unsuitable replacement for the Twin Cam .

On the subject of valve seats, again it suprises me to hear that an Engineering shop would refuse to fit them in a Twin Cam head. Modern valve seat material has better expansion properties than that of the original seats and are therefore more in balance with the expansion rate of the parent material as the head heats up. Although I prefer to fit seats having first frozen them in liquid nitrogen, seats can be fitted just as successfully by heating the head. A suitable punch or drift is then used to drive the seat into place. An experienced engineer using either method still gets a feel for how much effort is required as the seat is being driven into position. If it goes in too easily then the interference fit is incorrect and it should be removed.



Nick